1. Climate foundation
Hardiness zone: 4b / 5a
Wausau sits on the boundary between zones 4b (average annual extreme minimum of −25 to −20°F) and 5a (−20 to −15°F) on the current USDA map. The tool shows both because the line runs through the metro area, and because a yard’s microclimate — a low spot, an exposed hilltop, a south-facing wall — matters more than the map’s half-zone. By ZIP code, Wausau (54401 and 54403) and Schofield–Weston (54476) fall in zone 4b; Rothschild (54474) and Mosinee (54455) fall in 5a.
2023 USDA Plant Hardiness Zone Map. U.S. Department of Agriculture, Agricultural Research Service, with Oregon State University’s PRISM Climate Group. Based on 1991–2020 average annual extreme minimum temperatures. ZIP-code zones checked with phzmapi.org, which serves the 2023 map’s data by ZIP code.
https://planthardiness.ars.usda.gov/ · https://phzmapi.org/
https://planthardiness.ars.usda.gov/ · https://phzmapi.org/
Frost dates: ~May 15 and ~Oct 1
The frost dates are anchored to NOAA’s official 30-year climate normals for the Wausau Downtown Airport station (NOAA station USW00014897, “WAUSAU ASOS”). These are the probabilities NOAA publishes for that station (in spring, each percentage is the chance of a colder night after that date; in fall, the chance of one before it):
| Threshold | Last spring frost | First fall frost | Frost-free season |
|---|---|---|---|
| 36°F (frost possible) | May 4 (90%) · May 19 (50%) · May 31 (10%) | Sep 12 (10%) · Sep 25 (50%) · Oct 7 (90%) | 130 days (50%) |
| 32°F (frost) | Apr 24 (90%) · May 6 (50%) · May 21 (10%) | Sep 21 (10%) · Oct 4 (50%) · Oct 18 (90%) | 150 days (50%) |
| 28°F (hard freeze) | Apr 12 (90%) · Apr 26 (50%) · May 10 (10%) | Oct 1 (10%) · Oct 16 (50%) · Oct 31 (90%) | 173 days (50%) |
NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020 — annual/seasonal normals, frost and freeze probability variables (ANN-TMIN-PRBLST-T32FP50, ANN-TMIN-PRBFST-T32FP50, and related), station USW00014897.
https://www.ncei.noaa.gov/products/us-climate-normals · https://www.ncei.noaa.gov/data/normals-annualseasonal/1991-2020/access/USW00014897.csv
https://www.ncei.noaa.gov/products/us-climate-normals · https://www.ncei.noaa.gov/data/normals-annualseasonal/1991-2020/access/USW00014897.csv
Independent check: Wisconsin State Climatology Office, Marathon County Climate Profile. Average last freeze (32°F) May 6 and average first freeze October 3, computed for 1995–2024 from ACIS station data. That agrees with NOAA’s May 6 and October 4 to within a day.
https://climatology.nelson.wisc.edu/marathon-county-climate-profile
https://climatology.nelson.wisc.edu/marathon-county-climate-profile
Why the tool says ~May 15 rather than May 6. A “50% date” is a coin flip: half of all years still see a 32°F night after May 6, and one year in ten sees one after May 21. The tool plans around ~May 15, between the coin-flip date and the one-in-ten date and just ahead of NOAA’s May 19 median for the last 36°F night (the threshold the tool’s frost flags use), because a lost tomato crop costs more than a week of waiting. The fall date of ~Oct 1 sits three days ahead of NOAA’s Oct 4 median, erring toward an early frost, and the “~139 days” frost-free figure is simply the span between the two dates (NOAA’s 50% figure is 150). That is why the tool calls them its last- and first-frost dates rather than averages. The choice is ours, not NOAA’s; the underlying figures are above so readers can weigh it for themselves.
On the calendar. The planting chart shades frost risk from the same NOAA figures: solid through Apr 24, after which 9 springs in 10 still see a frost, fading to May 21, the one-in-ten date. In fall it builds from Sep 21, when 1 year in 10 has had a frost, to solid at Oct 18, when 9 in 10 have. The ~May 15 and ~Oct 1 planning dates are drawn as lines inside the bands. The Weather tab also treats any National Weather Service forecast that mentions frost or a freeze as frost risk, even on a night forecast above 36°F. The Weather Service lists a dawn frost under the day it falls on (“Monday: Patchy Frost then Sunny”), so the tool ties it to the night before, the one to cover.
2. Live forecast and frost-risk flags
The Weather & This Week tab pulls the current 7-day forecast for Wausau (44.9591°N, 89.6301°W) directly from the National Weather Service each time the page loads. Marathon County is served by the NWS Green Bay forecast office. Nothing is cached or edited by us — the numbers on the cards are the NWS numbers.
The tool flags any forecast overnight low of 36°F or colder as a frost risk. That matches the criteria National Weather Service offices use for Frost Advisories, which are set locally but typically read like NWS Wilmington’s: minimum temperatures “forecast to be 33 to 36 degrees” with conditions favorable for frost during the growing season. It is also deliberately conservative: valley floors and low yards routinely run several degrees colder than the airport reading. NOAA’s normals put the median last 36°F night at the Wausau airport on May 19 and the first on September 25.
National Weather Service API (api.weather.gov) — public data, no key required; endpoints
https://www.weather.gov/documentation/services-web-api · https://www.weather.gov/grb/ · Frost Advisory criteria: https://www.weather.gov/ilm/criteria
/points/{lat},{lon} and the returned /gridpoints/…/forecast. NWS Green Bay forecast office.https://www.weather.gov/documentation/services-web-api · https://www.weather.gov/grb/ · Frost Advisory criteria: https://www.weather.gov/ilm/criteria
Covering plants on a frost night. When the This Week front says to cover tender plants, it says how: old sheets, blankets, or cardboard boxes, put on before sundown, propped off the leaves and weighted to the ground, with plastic kept off the foliage, and taken off once it’s above freezing the next morning. When the forecast low is 28°F or colder it adds that covers buy only a few degrees and usually won’t save tender plants below about 28°F. Each point appears in guidance from at least two of the Extension services below, and most appear in all of them: covers work by holding in the soil’s heat, plants freeze where a cover touches them, and plastic is the material they warn about. These are their general recommendations, gathered by Wausau Pilot & Review; none of them reviewed this tool.
UW–Madison Extension: “Frost Protection Options” (Extension Marinette County, 2020); “Fruit and Frost”; “Extending the Garden Season.” Iowa State University Extension: “How to Protect Plants from Frost and Freeze” (reviewed 2024). Colorado State University Extension: GardenNotes #722, “Frost Protection and Extending the Growing Season.” University of Illinois Extension: Gardeners Corner, spring 2021. Purdue Extension: HO-93, “Autumn Garden Calendar”; HO-203, “Effects of Cold Weather on Horticultural Plants in Indiana.” Penn State Extension: “Pennsylvania Garden Tips” (Adams County). University of Minnesota Extension: “A Minnesota guide to garden timing” (a hard frost, 28°F or colder, kills most warm-season crops).
https://marinette.extension.wisc.edu/files/2020/10/Frost-Protection-Options.pdf · https://hort.extension.wisc.edu/articles/fruit-and-frost/ · https://hort.extension.wisc.edu/articles/extending-garden-season/ · https://yardandgarden.extension.iastate.edu/how-to/how-protect-plants-frost-and-freeze · https://extension.colostate.edu/resource/frost-protection-and-extending-the-growing-season/ · https://extension.illinois.edu/newsletters/archive/gardeners-corner/gardeners-corner-spring-2021 · https://www.extension.purdue.edu/extmedia/HO/HO-93.pdf · https://ag.purdue.edu/department/hla/extension/extension-publications-library/ext-pubs/ho-203-w.html · https://extension.psu.edu/programs/master-gardener/counties/adams/news/pa-garden-tips · https://extension.umn.edu/about/our-stories/news/yard-and-garden-news/a-minnesota-guide-to-garden-timing
https://marinette.extension.wisc.edu/files/2020/10/Frost-Protection-Options.pdf · https://hort.extension.wisc.edu/articles/fruit-and-frost/ · https://hort.extension.wisc.edu/articles/extending-garden-season/ · https://yardandgarden.extension.iastate.edu/how-to/how-protect-plants-frost-and-freeze · https://extension.colostate.edu/resource/frost-protection-and-extending-the-growing-season/ · https://extension.illinois.edu/newsletters/archive/gardeners-corner/gardeners-corner-spring-2021 · https://www.extension.purdue.edu/extmedia/HO/HO-93.pdf · https://ag.purdue.edu/department/hla/extension/extension-publications-library/ext-pubs/ho-203-w.html · https://extension.psu.edu/programs/master-gardener/counties/adams/news/pa-garden-tips · https://extension.umn.edu/about/our-stories/news/yard-and-garden-news/a-minnesota-guide-to-garden-timing
A hard freeze. When the night the front leads with is forecast at 28°F or colder, the tool calls it a hard freeze, as the National Weather Service does, and the headline, the line under the title, the Frost outlook box, and the forecast card say so. Covers come second, after what still helps: in spring, bringing seedlings that are hardening off and potted plants inside, with every plant-out window marked to wait; after mid-May, holding off on tender crops, with how long their planting windows stay open in case they need replanting; from July on, picking ripe and nearly ripe tender crops (full-size, glossy green tomatoes ripen indoors). When the hard freeze comes later in the week, the front still leads with tonight’s frost, gives both nights’ lows, and says what to do before the freeze.
What a hard freeze leaves standing. The front names only crops where at least two of the services below agree. In fall, kale, Brussels sprouts, and cabbage usually come through, while carrots, Swiss chard, lettuce, and cauliflower take only a light frost, and garlic planted for next year stays in the ground. In spring the sources don’t agree that peas, spinach, radishes, or onions come through 28°F unharmed, so the front says to cover them along with lettuce, and that potato tops killed by frost usually regrow from the tuber. These are the services’ general recommendations, gathered by Wausau Pilot & Review; none of them reviewed this tool.
National Weather Service: glossary, “Hard Freeze”; Public Information Statement 21-67 (2021), frost and freeze headlines. University of Minnesota Extension: “A Minnesota guide to garden timing”; “Planting vegetables in midsummer for fall harvest”; “Growing tomatoes in home gardens.” Iowa State University Extension: “How to Protect Plants from Frost and Freeze”; “Fall Planting of Vegetables”; “Can I ripen green tomatoes indoors before frost?”; “Cold and Freeze Damage to Garden Plants.” Purdue Extension: HO-66, “The Fall Vegetable Garden.” University of Maryland Extension: “Vegetables for Spring and Fall Planting.” University of Illinois Extension: “Ken Johnson wants you to plant a vegetable garden this fall” (2016). South Dakota State University Extension: “Fall Frost Tolerance of Common Vegetables.” Oregon State University Extension: “Plant cold-hardy vegetables now for a spring harvest.” NC State Extension: “Frost and Freeze Protection for Vegetable Crops.” North Dakota State University Extension: “Dakota Gardener: Preparing Transplants for the Outdoors”; “Frost scare,” Yard & Garden Report (2014; archived copy). Colorado State University Extension: “Ripening Tomatoes Indoors.” UW–Madison Extension: A2801, “Growing Vegetables at Home: Questions and Answers.” University of Vermont Extension: Plant Diagnostic Clinic, frost damage to vegetables (2023).
https://forecast.weather.gov/glossary.php?word=hard%20freeze · https://www.weather.gov/media/notification/pdf2/pns21-67frost_freeze_headlines.pdf · https://extension.umn.edu/about/our-stories/news/yard-and-garden-news/a-minnesota-guide-to-garden-timing · https://extension.umn.edu/planting-and-growing-guides/planting-vegetables-midsummer-fall-harvest · https://extension.umn.edu/vegetables/growing-tomatoes · https://yardandgarden.extension.iastate.edu/how-to/how-protect-plants-frost-and-freeze · https://yardandgarden.extension.iastate.edu/how-to/fall-planting-vegetables · https://yardandgarden.extension.iastate.edu/faq/can-i-ripen-green-tomatoes-indoors-frost · https://yardandgarden.extension.iastate.edu/how-to/cold-and-freeze-damage-garden-plants · https://www.extension.purdue.edu/extmedia/ho/ho-66-w.pdf · https://extension.umd.edu/sites/extension.umd.edu/files/2022-04/2%20VEGETABLES%20FOR%20SPRING%20AND%20FALL%20PLANTING%20and%20Summer.pdf · https://extension.illinois.edu/blogs/flowers-fruits-and-frass/2016-08-13-ken-johnson-wants-you-plant-vegetable-garden-fall · https://extension.sdstate.edu/fall-frost-tolerance-common-vegetables · https://extension.oregonstate.edu/news/plant-cold-hardy-vegetables-now-spring-harvest · https://vegetables.ces.ncsu.edu/news/frost-and-freeze-protection-for-vegetable-crops/ · https://www.ag.ndsu.edu/news/columns/dakota-gardener/dakota-gardener-preparing-transplants-for-the-outdoors · https://web.archive.org/web/20201023092540/https://www.ag.ndsu.edu/yardandgardenreport/2014-09-08/frost-scare · https://extension.colostate.edu/?p=12438 · https://hort.extension.wisc.edu/files/2021/11/A2801.pdf · https://uvm.edu/d10-files/documents/2024-11/PDC_POWfrost.pdf
https://forecast.weather.gov/glossary.php?word=hard%20freeze · https://www.weather.gov/media/notification/pdf2/pns21-67frost_freeze_headlines.pdf · https://extension.umn.edu/about/our-stories/news/yard-and-garden-news/a-minnesota-guide-to-garden-timing · https://extension.umn.edu/planting-and-growing-guides/planting-vegetables-midsummer-fall-harvest · https://extension.umn.edu/vegetables/growing-tomatoes · https://yardandgarden.extension.iastate.edu/how-to/how-protect-plants-frost-and-freeze · https://yardandgarden.extension.iastate.edu/how-to/fall-planting-vegetables · https://yardandgarden.extension.iastate.edu/faq/can-i-ripen-green-tomatoes-indoors-frost · https://yardandgarden.extension.iastate.edu/how-to/cold-and-freeze-damage-garden-plants · https://www.extension.purdue.edu/extmedia/ho/ho-66-w.pdf · https://extension.umd.edu/sites/extension.umd.edu/files/2022-04/2%20VEGETABLES%20FOR%20SPRING%20AND%20FALL%20PLANTING%20and%20Summer.pdf · https://extension.illinois.edu/blogs/flowers-fruits-and-frass/2016-08-13-ken-johnson-wants-you-plant-vegetable-garden-fall · https://extension.sdstate.edu/fall-frost-tolerance-common-vegetables · https://extension.oregonstate.edu/news/plant-cold-hardy-vegetables-now-spring-harvest · https://vegetables.ces.ncsu.edu/news/frost-and-freeze-protection-for-vegetable-crops/ · https://www.ag.ndsu.edu/news/columns/dakota-gardener/dakota-gardener-preparing-transplants-for-the-outdoors · https://web.archive.org/web/20201023092540/https://www.ag.ndsu.edu/yardandgardenreport/2014-09-08/frost-scare · https://extension.colostate.edu/?p=12438 · https://hort.extension.wisc.edu/files/2021/11/A2801.pdf · https://uvm.edu/d10-files/documents/2024-11/PDC_POWfrost.pdf
3. Vegetable planting windows
The primary reference for when to start, transplant, and sow vegetables is UW–Madison Extension’s statewide planting guide. Its table gives dates for Madison, and its own footnote is the key to using it here:
Vegetable Cultivars and Planting Guide for Wisconsin Gardens (A1653). A.J. Bussan, Judy Reith-Rozelle, and Karen Delahaut. University of Wisconsin–Extension, Cooperative Extension, 2008 (SR-07-2011). Planting-guide table, p. 5, footnote a: “Plant 1–2 weeks later along the lower lake shore and in the central part of state and 2–3 weeks later in northern counties.”
https://learningstore.extension.wisc.edu/Assets/pdfs/A1653.pdf
https://learningstore.extension.wisc.edu/Assets/pdfs/A1653.pdf
Method. For each vegetable we took the Madison date from A1653, shifted it 1–2 weeks later per the footnote (Marathon County is “the central part of state”), and then checked the result against the NOAA frost probabilities above — pushing frost-tender crops (tomatoes, peppers, basil, cucurbits) toward the later end of the range and letting frost-hardy crops (peas, spinach, brassicas, onions, potatoes) sit at the earlier end. Window end dates and fall succession sowings reflect days-to-maturity counted back from the ~Oct 1 first frost. Varietal suggestions in the guides (Early Girl, Music garlic, Winterbor and Red Russian kale, and so on) come from A1653’s cultivar lists and the Wisconsin Horticulture pages below. Section 4 checks every result against other institutions.
Wisconsin Horticulture — Vegetables. University of Wisconsin–Madison Division of Extension.
https://hort.extension.wisc.edu/vegetables/
https://hort.extension.wisc.edu/vegetables/
4. Cross-check: every window, at least two sources
Every window in the tool is checked against published guidance from at least two institutions: UW–Madison Extension, and the Extension services of the University of Minnesota (the same climate band), Purdue, Cornell, the University of Illinois, Iowa State, Penn State, the University of Maryland, North Dakota State, the University of Missouri, NC State, Ohio State, South Dakota State, and the University of New Hampshire, plus the Morton Arboretum, the Missouri Botanical Garden, the Chicago Botanic Garden, the Lady Bird Johnson Wildflower Center, and Montana State University’s Western Agricultural Research Center. All UW–Madison pages count as one institution, however many we cite. The original 31 plants were checked on September 25, 2026, and the 50 added on September 29 were checked the same way before they went in; five of those were removed on October 3 under the safety rule in section 6. Three more, suggested on October 4, were checked the same way before they went in. The table shows what each source says, converted to Wausau dates; follow a plant’s “see what each says” link in the tool to land on its row.
How we converted. Advice given relative to frost (“4–6 weeks before the last frost”) is counted from the tool’s ~May 15 and ~Oct 1 dates, or from the source’s own frost reference where it names one: Purdue’s calendar counts from a one-in-ten frost date, which is May 21 and September 21 for Wausau. Seed-starting lead times (weeks indoors) are counted back from the tool’s own transplant window, and bloom times from warmer states run a few weeks ahead of ours. Confirmed means at least two institutions support the tool’s dates to within about a week. Harvest windows follow from each planting window plus the days-to-harvest figures in the guides (checked against Extension in the September 9 review below) and end at the ~Oct 1 frost for frost-tender crops; bloom windows were checked against published bloom times.
| Plant | In the tool | What the sources say | Status |
|---|---|---|---|
| Vegetables | |||
| Tomato | Indoors Apr 10–25 · Plant May 25–Jun 10Harvest Jul 25–Sep 30 | UW (A1653): indoors Apr 15, out May 20 in Madison, 1–2 weeks later here. Minnesota: 5–6 weeks indoors from early April; transplant mid-to-late May into the first week of June. Purdue: after the last frost (May 21 on its basis). Maryland: 5–6 weeks indoors. | Confirmed |
| Bell Pepper | Indoors Apr 1–15 · Plant Jun 5–15Harvest Aug 1–Sep 25 | UW (A3687): northern growers wait two weeks past the June 1 southern date. Minnesota: transplant in early June, after 9 weeks indoors. Purdue: at least two weeks after the last frost (Jun 4 on its basis). Maryland: 8–10 weeks indoors. | Confirmed |
| Broccoli | Indoors Apr 1–10 · Plant May 5–20 · Sow Jul 1–15Harvest Jun 25–Jul 20, Sep 15–Oct 15 | UW (A1653): indoors Mar 15, out May 1 in Madison, 1–2 weeks later here. Cornell: 5–6 weeks indoors; transplant after the last frost (May 14 in Ithaca); with an Oct 1 frost, set fall plants out by Jul 31–Aug 10. Purdue: fall crops 4–8 weeks before the first frost. Maryland: 4–6 weeks indoors. (Purdue would allow spring transplants from mid-April; Minnesota’s table allows 10–11 weeks indoors.) | Confirmed |
| Cucumber | Sow Jun 1–20Harvest Jul 15–Sep 15 | UW (A3688): not before May 27 in southern Wisconsin, 1–2 weeks later in the north. Minnesota: sow from the last week of May through June. Purdue: at least two weeks after the last frost (Jun 4 on its basis). | Confirmed |
| Zucchini & Summer Squash | Sow May 25–Jun 20Harvest Jul 10–Sep 20 | UW (A1653, A3688): one schedule for every summer squash, May 20 in Madison, 1–2 weeks later here; 50–60 days to first harvest. Minnesota: sow from the last week of May through June. Cornell: once the soil is warm, about Jun 1; last planting Jul 15. Illinois: pattypan, crookneck, straightneck, and zucchini all plant after frost. (Purdue waits until two weeks after its one-in-ten frost date, Jun 4.) | Confirmed |
| Green Beans | Sow May 25–Jul 1Harvest Jul 15–Sep 20 | UW (A1653): May 10 in Madison, 1–2 weeks later here. Minnesota: mid-May to early July. Purdue: after the last frost (May 21 on its basis). | Confirmed |
| Snap Peas | Sow Apr 20–May 15Harvest Jun 20–Jul 20 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Minnesota: mid-April to early May. Cornell: about Apr 15, as early as the soil can be worked. Purdue: 4–6 weeks before the last frost (Apr 9–23). | Confirmed |
| Lettuce | Sow Apr 25–Aug 15Harvest May 25–Oct 1 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Cornell: about Apr 15; last sowing of leaf lettuce Aug 10 with an Oct 1 frost. Purdue: 2–4 weeks before the last frost (Apr 23–May 7); fall sowings 4–8 weeks before the first frost. | Confirmed |
| Spinach | Sow Apr 15–May 10, Aug 1–15Harvest May 20–Jun 20, Sep 10–Oct 31 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Minnesota: mid-April; fall sowing in early August. Cornell: about Apr 15; last fall sowing Aug 10 with an Oct 1 frost. Purdue: 4–6 weeks before the last frost (Apr 9–23). | Changed Sept 25fall sowing moved from Aug 15–Sep 1; the April 15 sowing, flagged earlier, is now confirmed |
| Carrots | Sow May 1–Jun 15Harvest Jul 1–Oct 15 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Purdue: 2–4 weeks before the last frost (Apr 23–May 7). Cornell: as early as about Apr 15. The tool starts at the late end. | Confirmed |
| Radishes | Sow Apr 20–Sep 1Harvest May 15–Oct 1 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Cornell: about Apr 15. Purdue: 4–6 weeks before the last frost (Apr 9–23); fall sowings at least 4 weeks before the first frost. | Confirmed |
| Sweet Corn | Sow May 20–Jun 5Harvest Aug 15–Sep 15 | UW (A1653): May 10 in Madison (May 25 for supersweets), 1–2 weeks later here. Minnesota: mid-to-late May into the first week of June. Purdue: after the last frost, in soil of at least 60°F. | Confirmed |
| Potatoes | Plant May 1–25Harvest Aug 15–Oct 1 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Minnesota: mid-April to mid-May. Purdue: 4–6 weeks before the last frost (Apr 9–23). Cornell: after the last frost (May 14 in Ithaca). The tool sits in the middle of that range. | Confirmed |
| Onions (sets) | Plant Apr 25–May 15Harvest Aug 1–Sep 15 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here. Minnesota: mid-April. Cornell: about Apr 15. Purdue: 4–6 weeks before the last frost (Apr 9–23). | Confirmed |
| Pumpkin | Sow May 25–Jun 5Harvest Sep 15–Oct 10 | UW (A1653): May 10 in Madison (plants May 20), 1–2 weeks later here. Minnesota: late May to early June. (Purdue waits until two weeks after its one-in-ten frost date, Jun 4.) | Confirmed |
| Kale | Sow Apr 20–Jul 10Harvest Jun 15–Oct 31 | Minnesota: mid-April to early July. Cornell: about Apr 15; last sowing Jul 31 with an Oct 1 frost. Purdue: 4–6 weeks before the last frost (Apr 9–23). UW’s A1653 lists only a fall sowing (Jun 25 in Madison). | Changed Sept 25sowing moved from May 1–Jul 15, which also lines the first harvest up with kale’s 55–65 days |
| Garlic | Plant Oct 1–25Harvest Jul 10–31 | UW (A3785, Wisconsin Horticulture): plant in October before the ground freezes. Minnesota: plant 1–2 weeks after the first killing frost, around early October; harvest in mid-July. Illinois: plant in October. | Confirmed |
| Kohlrabi | Sow Apr 20–May 10, Jul 15–Aug 1Harvest Jun 1–Jul 10, Sep 10–Oct 20 | UW (A1653): Apr 15 in Madison, 1–2 weeks later here (Apr 22–29); 50–60 days to harvest. Minnesota: direct seed mid-April to early May and again in July (early August in its planting table); pick at 2–3 inches. Cornell: as soon as the ground can be worked, about Apr 15; last fall planting Jul 31. Purdue: hardy, 4–6 weeks before the last frost (Apr 9–23 on its basis) and again 4–8 weeks before the first fall frost (Jul 27–Aug 24). | Confirmed |
| Hot Pepper | Indoors Apr 1–15 · Plant Jun 5–15Harvest Aug 10–Sep 30 | UW (A1653, A3687): one ‘Pepper’ row covers sweet and hot types, indoors Apr 1 and out Jun 1 in Madison, 1–2 weeks later here (indoors Apr 8–15, out Jun 8–15); 60–70 days to first harvest. Minnesota: about 8–9 weeks indoors (8 on its pepper page, 9 in its seed-starting table) and transplant in early June once nights stay above 50°F, with sweet and hot types handled together. Purdue: at least two weeks after the last frost (Jun 4 on its basis). Cornell: transplant after the last frost (about May 14); last planting Jun 30. Maryland: 8–10 weeks indoors, up to 12 for some types; most hot types take 70–85 days from transplanting, habaneros 90–120. New Hampshire: 8 weeks before the last frost for hot peppers too. | Confirmed |
| Cauliflower | Indoors Apr 1–10 · Plant May 1–20 · Sow Jul 1–15Harvest Jun 20–Jul 20, Sep 15–Oct 20 | UW (A1653): indoors Mar 15, out May 1 in Madison, 1–2 weeks later here (indoors Mar 22–29, out May 8–15); 50–60 days from transplant. Minnesota: seeds indoors in April, about 4 weeks to transplant size; a 50–60 day, heat-tolerant variety for spring; seed the fall crop in early to late July, indoors or direct. Cornell: early spring, about Apr 15 (later if transplanted); last planting Jul 15 for late types and Aug 10 for early types. Purdue: semi-hardy, 2–4 weeks before the last frost (Apr 23–May 7 on its basis). | Confirmed |
| Brussels Sprouts | Indoors Apr 20–May 20 · Plant May 25–Jun 20Harvest Sep 25–Oct 31 | UW (A1653): seed outdoors May 15 in Madison, 1–2 weeks later here (May 22–29); 90–100 days. Iowa State: seeds indoors 4–5 weeks ahead and plants out early to mid-May in central Iowa (about two weeks later here); ready 85–110 days after transplanting, typically late September to early November, and light frosts improve flavor. Maryland: 4–6 week old transplants set out 90–100 days before the first frost (by about Jun 23–Jul 3 here); 80–100 days from transplant; harvest after frost. Minnesota: a fall crop, transplants early June in its planting table; harvest late September to late October, and plants stay in the garden down to about 20°F. Cornell: last planting Jun 30. Purdue: transplant by midsummer for fall. South Dakota State: best after several moderate freezes (24–28°F). | Confirmed |
| Cabbage | Indoors Apr 1–10 · Plant Apr 28–May 15 · Sow Jul 1–10Harvest Jun 28–Jul 25, Sep 20–Oct 25 | UW (A1653): early cabbage indoors Mar 15, out May 1 in Madison (indoors Mar 22–29, out May 8–15 here), 60–70 days; late cabbage seeded outdoors May 15 (May 22–29 here), 90–100 days. Minnesota: start indoors in early April or 4–6 weeks before transplanting; direct seed a fall crop in early July; 60–100 days to mature. Cornell: early spring, about Apr 15; last transplanting Jun 30 (late), Jul 15 (medium) or Jul 31 (early types). Purdue: hardy, 4–6 weeks before the last frost (Apr 9–23 on its basis) and 4–8 weeks before the first fall frost (Jul 27–Aug 24). | Confirmed |
| Swiss Chard | Sow Apr 30–May 20Harvest Jun 10–Oct 25 | UW (A1653; Wisconsin Horticulture): sow Apr 15 in Madison, 1–2 weeks later here (Apr 22–29), 40–50 days; Wisconsin Horticulture says from about a month before the last frost through midsummer. Minnesota: sow early to mid-May, because cold spells can make young plants bolt; one sowing gives leaves from spring through fall. Cornell: as soon as the ground can be worked, about Apr 15; last planting Jul 31. Purdue: semi-hardy, 2–4 weeks before the last frost (Apr 23–May 7 on its basis). | Confirmed |
| Parsnips | Sow Apr 25–May 20Harvest Apr 5–30, Oct 10–31 | UW (A1653): sow Apr 15 in Madison, 1–2 weeks later here (Apr 22–29); 100–120 days. Minnesota: start planting parsnips May 1; seed can take up to three weeks to germinate; leave roots in the ground until late fall or even early spring. Purdue: semi-hardy, 2–4 weeks before the last frost (Apr 23–May 7 on its basis). Iowa State: sow in early to mid-spring, 100–120 days; frost develops the flavor, and roots can overwinter and be dug the next spring before they flower. South Dakota State: best harvested after several moderate freezes (24–28°F). Wisconsin’s invasive-species rule restricts wild parsnip but exempts the garden vegetable form (NR 40.05(2)(b)35). | Confirmed |
| Winter Squash | Sow May 27–Jun 10Harvest Sep 15–Oct 10 | UW (A1653, A3688): plants out May 20 in Madison (seed as early as May 10), 1–2 weeks later here (May 27–Jun 3); 90–120 days to first harvest. Minnesota: sow late May to early June once soil is 65°F, or transplant after about 4 weeks indoors; pick before a hard freeze. Cornell: transplant after the soil is warm, about Jun 1. Purdue: at least two weeks after the last frost (Jun 4 on its basis). South Dakota State: 80–115 days; Illinois: acorn types 80–100 days, harvest in September or October before heavy frosts. | Confirmed |
| Cantaloupe | Indoors May 5–15 · Plant Jun 1–10Harvest Aug 25–Sep 30 | UW (A1653, A3688): indoors May 1, plants out May 20 in Madison, 1–2 weeks later here (indoors May 8–15, out May 27–Jun 3); 80–90 days (A3688: 90–125), and dark plastic mulch can hasten maturity by 1–3 weeks. Iowa State: plant mid-May in central Iowa (about two weeks later here) once soil is 60–70°F, starting transplants 3–4 weeks ahead; last practical sowing date Jun 20 in Iowa. Cornell: transplant after the soil is warm, about Jun 1; last planting Jun 10. Purdue: at least two weeks after the last frost (Jun 4 on its basis). Minnesota: mid-May in its planting table. | Confirmed |
| Watermelon | Indoors May 5–15 · Plant Jun 1–10Harvest Aug 28–Sep 30 | UW (A1653, A3688): plants out May 20 in Madison (indoors May 1), 1–2 weeks later here (indoors May 8–15, out May 27–Jun 3); 75–90 days (A3688: 75–125). Iowa State: plant mid-May in central Iowa (about two weeks later here) once soil is 60–70°F, starting transplants 3–4 weeks ahead; last practical sowing date Jun 20 in Iowa. Cornell: transplant after the soil is warm, about Jun 1; last planting Jun 10. Purdue: at least two weeks after the last frost (Jun 4 on its basis). Minnesota: mid-May in its planting table, with hot caps to seed earlier. | Confirmed |
| Herbs | |||
| Basil | Indoors Apr 10–25 · Plant Jun 1–15Harvest Jul 1–Sep 15 | Iowa State: start indoors 4–5 weeks before the last frost; plant out after frost danger, in soil of 60°F. Illinois: plant out after frost, in warm soil. Minnesota: 5–6 weeks indoors from early April (its table lists ornamental basil). Iowa State and Illinois both describe harvests running into fall. | Confirmed |
| Dill | Sow May 10–Jun 15Harvest Jun 20–Sep 1 | Minnesota: sow after the last frost. Illinois: sow 1–2 weeks before it (May 1–8 here). The tool’s window starts between the two; both suggest repeat sowings into summer. | Confirmed |
| Chives | Plant May 15–Jun 10Harvest May 1–Oct 1 | UW (Wisconsin Horticulture): set seedlings out after the danger of frost is past. Minnesota: plant rooted clumps in spring after frost danger has passed. Clumps already in the ground are cut from spring on. | Changed Sept 25planting moved from Apr 20–May 20 |
| Parsley | Indoors Mar 10–25 · Plant May 15–30Harvest Jun 15–Oct 15 | UW (Wisconsin Horticulture): start indoors 8–10 weeks before the last frost (Mar 6–20). Minnesota: 6–8 weeks (Mar 20–Apr 3). Both: plant out after frost; parsley takes light frost and produces into fall. | Confirmed |
| Cilantro | Sow Apr 25–May 31, Aug 1–15Harvest Jun 10–Aug 10, Sep 10–Oct 15 | UW: sow in early spring, when lettuce goes in, then re-sow every 2–3 weeks; seed a fall crop in mid-August; leaves are ready in 45–80 days, and summer sowings bolt. Iowa State (PM 1893) also says to sow outdoors in early spring, and Purdue’s calendar plants lettuce 2–4 weeks before the last frost (counted from May 21, the one-in-ten date used for Wausau), so the spring sowing opens about Apr 25. Minnesota: cilantro is a cool-season herb that tolerates cooler soil, and its midsummer table gives 60–70 days to maturity (Jul 23–Aug 2 counting back from Oct 1) and survival of light frost, which with UW’s mid-August supports an Aug 1–15 fall sowing; NDSU and Penn State say it does best in spring and fall and should be re-sown every 3–4 or 2–4 weeks. Illinois sows after frost danger is past (mid-May here) and re-sows every 3–4 weeks, while Maryland re-sows every 2–3 weeks. | Confirmed |
| Rosemary | Plant May 20–Jun 10Harvest Jun 15–Oct 1 | UW: winter hardy only to zone 8a, so it is grown as a potted plant in Wisconsin, set outdoors for summer and brought in before first frost (or dug 2–3 weeks before the expected first fall frost if planted in soil); seed is not recommended and cuttings are best. Missouri Botanical Garden (zones 8–10): containers go outside in mid-spring after the last frost date, which means after mid-May here, and wintering it indoors is often difficult; Maryland moves it out once the danger of a hard frost has passed and back in when nights dip into the low 40s. Minnesota lists rosemary as a warm-season herb that prefers soil near 60°F and says to transplant after frost danger; NDSU says rosemary can be grown only as an annual in the north. Illinois: a tender perennial best kept in containers, cut as needed through the growing season and brought in just before a frost; Iowa State likewise calls it a tender perennial that can be overwintered indoors in a sunny window, harvested at no more than one-third at a time. | Confirmed |
| Thyme | Plant May 15–Jun 15Harvest Jun 1–Sep 1 | Illinois: a perennial that is much easier from divisions or cuttings than from seed; stems can be cut through the season, best just before flowering; poorly drained soil, especially over winter, shortens its life. Chicago Botanic Garden rates common thyme hardy in zones 4–8 (an archived page) and Missouri Botanical Garden in zones 5–9, so Wausau (zone 4b/5a) sits at the cold edge; Missouri also says to harvest leaves throughout the summer. Minnesota: thyme is a cool-season herb, transplanted after frost danger (mid-May here) once soil holds 50°F or warmer; creeping thyme can be divided in early spring and hardy perennial herbs get 2–5 inches of mulch; Iowa State likewise divides perennial herbs in early spring and sets out transplants after frost danger. Maryland and Penn State mulch perennial herbs 4 inches deep after the ground freezes, and Cornell says perennial herbs can be clipped until late August, stopping about a month before frost (about Sep 1 here). | Confirmed |
| Sage | Indoors Mar 20–Apr 10 · Plant May 15–Jun 10Harvest Jun 15–Sep 1 | UW: hardy in zones 4a–10b; grow from seed by sowing at the average last-frost date or starting indoors 6–8 weeks earlier (about Mar 20–Apr 3 here), and expect about 75 days from planting to the first harvest. Missouri Botanical Garden rates common sage hardy in zones 4–8; Illinois says it needs very well-drained soil over winter and that cuttings beat seed, which can take years to give a harvest. Minnesota lists sage as a cool-season herb, started indoors 6–8 weeks before transplanting after frost danger; Maryland sets sage out after the danger of frost has passed and prefers cuttings or transplants because seed is slow. Cornell says perennial herbs can be clipped until late August and harvest should stop about a month before frost, and the Illinois blog also limits fall cutting so new growth can harden off. | Confirmed |
| Mint | Plant May 15–Jun 15Harvest Jun 1–Sep 1 | Illinois: an extremely hardy perennial that spreads aggressively by underground rhizomes; grow it in containers above ground (bottomless sunk pots do not always hold it), remove flower spikes to keep flavor, and divide every 3–4 years. Maryland: grow it in a 12–16 inch container, or a bottomless pot sunk with about an inch above soil, and space plants 18 inches apart; Penn State says 3- to 5-gallon pots buried with the rim an inch above ground, and Iowa State a large perforated container sunk with the rim about 1 inch above ground. Minnesota: hardy perennial mints can spread aggressively; herbs are transplanted after frost danger (mid-May here) and hardy perennials mulched 2–5 inches. Cornell says perennial herbs can be clipped until late August, stopping about a month before frost (about Sep 1 here). | Confirmed |
| French Tarragon | Plant May 15–Jun 15Harvest Jun 15–Sep 1 | Illinois: true French tarragon is available only as plants from cuttings or root divisions because its flowers are sterile; seed sold as tarragon is the taller, coarser Russian tarragon with inferior flavor; it needs well-drained soil, does not overwinter in poorly drained soil, and is divided every 3–4 years. Iowa State: French tarragon has sterile seed and must be propagated by division or cuttings; in Iowa harvest in June for vinegar and early to mid-July for drying, which runs about two weeks later here; Maryland: propagate by root cuttings or division and protect it in winter in cold climates. NDSU: French tarragon is hardy in zone 4 if given sufficient winter protection and is set out as greenhouse transplants, while Russian tarragon is even hardier but grows to 6 feet and spreads by seed; Missouri Botanical Garden lists French tarragon at zones 5–8 (the plain species, often Russian, at 3–7) and says wet winter soil is a common cause of loss. Minnesota says to transplant herbs after frost danger (mid-May here), and Cornell says perennial herbs can be clipped until late August, stopping about a month before frost. | Confirmed |
| Fennel | Sow May 15–Jun 10Harvest Jul 10–Oct 15 | UW: a short-lived perennial hardy in zones 4a–9b but often grown as an annual in cooler climates; sow after the last spring frost (mid-May here), or start indoors 4–6 weeks before it; leaf types such as ‘Bronze’ mature in about 60 days, seeds ripen in fall, and it tolerates light frost. Illinois: herb fennel is best direct sown in spring after frost is past and does not transplant well because of its taproot; Florence fennel is direct sown mid-June to July so the bulbs form in the cool late-summer weather. Iowa State: sow directly because fennel does not transplant well; green and bronze types reseed, and bulb types need a longer season. Maryland: it grows easily from seed planted in spring, thinned to 10–12 inches and staked at 18 inches. | Confirmed |
| German Chamomile | Indoors Mar 20–Apr 5 · Plant May 15–31 · Sow Apr 25–May 15Harvest Jul 1–Oct 1 | UW: sow directly shortly before the average last frost (about Apr 24–May 14 here), or start indoors 6–8 weeks before it (about Mar 20–Apr 3) and transplant after the last frost; plants bloom from early to midsummer until seed ripens or, if deadheaded, until frost. Missouri Botanical Garden (German chamomile, zones 2–8): plant seed shortly before the last spring frost date, or start it indoors 6–8 weeks earlier and plant out at the last frost, with flowers in mid-summer and continued flowering to frost; its June–August bloom is for St. Louis and runs several weeks later here. NDSU calls German chamomile an easily grown annual that reseeds readily. Roman chamomile (Chamaemelum nobile) is a creeping perennial, zones 4a–9b at UW and 4–9 at Missouri Botanical Garden, that can be aggressive and has a more bitter tea. | Confirmed |
| Oregano | Indoors Mar 25–Apr 15 · Plant May 20–Jun 15Harvest Jun 15–Sep 1 | Illinois: Greek oregano (Origanum vulgare var. hirtum) is the true culinary oregano and is marginally hardy in zone 5; get plants grown from cuttings because seed-grown plants often do not come true, sow any seed uncovered, and mulch with evergreen boughs or straw after the soil freezes, removing it as growth resumes. NDSU: Greek and Italian types are hardy in zone 4 if given winter protection, and oregano is usually started from seed in a greenhouse and transplanted after frost threats have passed (mid-May here); Minnesota lists oregano as a warm-season herb preferring soil near 60°F and starts herb seed indoors 6–8 weeks before transplanting. Missouri Botanical Garden rates both Greek and common oregano hardy in zones 4–8, best from cuttings of flavorful plants (seed-grown plants can lack flavor), with the best flavor just before flowering; Maryland says it is a hardy perennial grown from seed or division and thinned to 10–12 inches. Iowa State says to harvest leaves before flowering with a second cutting later (September in Iowa), while Cornell says perennial herbs can be clipped until late August and stopped about a month before frost, so the bar ends about Sep 1. | Confirmed |
| Flowers, perennials, grasses, and shrubs | |||
| Zinnia | Sow May 25–Jun 10Bloom Jul 25–Oct 1 | UW (Wisconsin Horticulture) and Minnesota: sow after frost, in soil of 60–70°F; both describe bloom continuing until frost. | Confirmed |
| Sunflower | Sow May 20–Jun 10Bloom Jul 25–Sep 20 | Minnesota: sow after the danger of frost has passed. Iowa State: early May in central Iowa, whose last frost comes two to three weeks earlier (late May to early June here); bloom 70–100 days after planting. | Confirmed |
| Marigold | Indoors Apr 1–15 · Sow May 25–Jun 10Bloom Jun 25–Oct 1 | Minnesota: start French and gem types indoors in early April (5–6 weeks); direct-sow once soil reaches 65°F; blooms until frost. UW (Wisconsin Horticulture): about 8 weeks indoors; direct-sow in soil above 65°F. Illinois: blooms May–October. | Confirmed |
| Petunia | Indoors Mar 10–25 · Plant May 20–Jun 5Bloom Jun 15–Oct 1 | Minnesota: 10–12 weeks indoors (about March 1 in northern climates); plant out once frost danger has passed and soil nears 60°F. Iowa State: start 10 weeks before the outdoor planting date (Mar 11–27 for the tool’s window); plant after frost; blooms all summer. Illinois: blooms May–October. | Confirmed |
| Impatiens | Plant May 25–Jun 10Bloom Jun 15–Sep 25 | Iowa State: plant after the last frost (New Guinea types about two weeks later); blooms continuously until the first fall frost. Illinois: blooms May–October. The tool waits until late May because impatiens stall in nights below 50°F. | Confirmedlater than required |
| Purple Coneflower | Plant May 10–Jun 15Bloom Jul 1–Sep 15 | Iowa State: divide purple coneflower in spring. Penn State: spring and autumn are the times to divide perennials, when they are not in bloom; purple coneflower blooms late June to early September. Illinois: blooms June–August, a few weeks ahead of Wausau. | Confirmed |
| Daylily | Plant May 1–Jun 15Bloom Jun 25–Aug 15 | Minnesota: plant as soon as the soil can be worked; peak bloom July to early August in Minnesota. Iowa State: divide in spring or late summer. Illinois: bloom season May–September. | Confirmed |
| Peony | Plant Sep 15–Oct 15Bloom Jun 1–25 | UW (Wisconsin Horticulture): plant bare-root peonies in September or October. Iowa State: September to early October. Minnesota: fleshy-rooted peonies are best divided in fall. Illinois: blooms May–June, a few weeks ahead of Wausau. | Confirmed |
| Hosta | Plant May 1–Jun 15Bloom Jul 1–Aug 31 | Minnesota: spring is generally the best time to plant, and to divide. Iowa State: divide in spring or late summer. Illinois: blooms June–August; the Morton Arboretum: early summer to midsummer, both a little ahead of Wausau. | Changed Sept 25the bar now shows bloom (it showed the whole leaf season, Jun 1–Sep 20) |
| Common Lilac | Plant May 1–Jun 1Bloom May 15–Jun 5 | Minnesota: container-grown shrubs can be planted any time during the growing season; lilacs bloom mid-to-late May. Iowa State: mid-March to early June works for most shrubs. Illinois: blooms in late spring. | Confirmed |
| Begonia | Indoors Mar 5–Apr 5 · Plant May 25–Jun 10Bloom Jun 15–Oct 1 | Iowa State: pot tuberous begonia tubers 8–10 weeks before the average last frost (Mar 6–20 counting from May 15), with flowering starting 12–14 weeks after potting; plant out once frost danger is past. Minnesota: tubers started in March or early April bloom in July; transplant after all danger of frost (late May or early June), and the care schedule lists summer bulbs for May 25–Jun 14. UW (Portage County calendar): tubers indoors early in March, out in May. Missouri Botanical Garden (set wax begonias out after the last frost; bloom June to frost), Illinois (wait for warm soil and air; May–October) and Cornell (very frost-sensitive; late spring to early fall) put wax begonia bloom three to four weeks ahead of Wausau. | Confirmed |
| Dahlia | Indoors Apr 1–20 · Plant May 25–Jun 10Bloom Jul 25–Oct 1 | Iowa State: pot tubers indoors in early April (6–8 weeks before planting out) for earlier bloom, and plant outdoors after the danger of frost is past — mid-May in central Iowa, a week later in northern Iowa. Cornell: start tubers indoors 6 weeks before the last frost (about Apr 3 here); dahlias bloom from midsummer to the first frost. Minnesota: the care schedule puts summer bulbs at May 25–Jun 14, and the Arboretum says to wait until mid-to-late May. Illinois and Missouri Botanical Garden allow planting 1–2 weeks before the last frost or starting earlier in pots, so the tool’s post-frost window is later than they require; MOBOT lists July–September bloom, about four weeks ahead of Wausau. | Confirmed |
| Pansy | Plant Apr 20–May 15, Aug 25–Sep 10Bloom Apr 25–Jun 30, Sep 5–Oct 31 | Iowa State: plant early to mid-April for spring color, swap in summer annuals in May, and plant again in early September for color until it snows (Iowa’s spring dates run about two weeks ahead of Wausau’s, and its fall frost comes a little later). Missouri Botanical Garden: set out plants in early spring; bloom April–June until summer heat ends it. UW (Portage County calendar): set out pansies when the ground is workable. Illinois: pansies are cool-season plants that fade in the heat of late May and June; Missouri Extension: September is the ideal fall planting month there, and Missouri’s fall frost comes later than Wausau’s, so plant earlier here. | Confirmed |
| Zonal Geranium | Indoors Mar 10–Apr 5 · Plant May 20–Jun 5Bloom Jun 10–Oct 1 | Minnesota: plant after any chance of frost has passed and the soil reaches 60°F; seed goes in mid-January. Iowa State: plant after the danger of frost, typically mid-to-late May in Iowa (about two weeks later here). UW: keep potted geraniums indoors until the threat of frost has passed (Wisconsin Horticulture) and set stored plants out after the last frost (Portage County calendar). Cornell: plant outside after frost danger has passed, and wake bare-root plants 6–8 weeks before the last frost; Illinois lists bloom May–October. | Confirmed |
| Cigar Plant (Cuphea) | Plant May 25–Jun 10Bloom Jun 10–Oct 1 | Missouri Botanical Garden: Cuphea ignea, called firecracker plant or cigar flower, is hardy only in zones 10–12 and is grown in St. Louis as an annual, container plant or houseplant, blooming late spring to frost. Iowa State (Reiman Gardens): the cigar plant or cigar flower, including the cultivar ‘Firecracker’ (Cuphea x purpurea), survives only as an annual in northern climates and blooms from planting until the first fall frost. Chicago Botanic Garden and NC State: firecracker plant is a tropical perennial that likes heat and sun (NC State: intolerant of frost, blooming late spring to the first frost). Minnesota: the care schedule’s best time for annuals is the last week of May through June; no source gives a Cuphea-specific date, so the tool plants after frost. | Confirmedlater than required |
| New England Aster | Plant May 10–Jun 15Bloom Aug 25–Oct 15 | UW (Wisconsin Horticulture): asters are best planted in spring, bloom late in the year, and are divided every two or three years in spring. Iowa State: aster divisions in spring (division table); pinch the buds a couple of times before July; blooms late summer to frost. Minnesota: perennials go in from the last week of May through August, and fall-blooming perennials are divided in spring. Illinois (August–October), NDSU (August–September), Missouri Botanical Garden (August–September, pinching before mid-July) and Ohio State (late summer through October) agree on late-summer-to-fall bloom. | Confirmed |
| Black-Eyed Susan | Indoors Mar 10–Apr 5 · Plant May 15–Jun 15 · Sow May 1–25Bloom Jul 1–Oct 1 | Minnesota: start rudbeckia (black-eyed Susan) seed indoors in early March, 10–11 weeks before transplanting; perennials go in from the last week of May. Cornell: R. hirta seed indoors 6–8 weeks before the last frost (Mar 20–Apr 3 here), or sown outdoors in spring. Missouri Botanical Garden: seed indoors about Mar 1 in St. Louis (roughly four weeks later here), sown outdoors or set out as plants at the last frost date, blooming June–September for both species. UW (Wisconsin Horticulture): early-sown seed, indoors or outdoors, flowers the same season and seedlings go out once frost risk is past; Iowa State: spring division, every 3–4 years; Illinois: R. hirta blooms June–October, R. fulgida July–October. | Confirmed |
| Coreopsis | Plant May 10–Jun 15, Aug 20–Sep 15Bloom Jun 25–Sep 15 | Iowa State: coreopsis can be divided in spring or late summer/fall (mid-August through September), and container perennials go in mid-April through May there, two to three weeks later here. Minnesota: perennials go in from the last week of May, and spring- and summer-blooming perennials can be divided in fall; Penn State: spring and autumn are the times to divide, September preferred, allowing 4–6 weeks before the ground freezes. Cornell: move seedlings out after frost danger has passed; divide every 2–3 years in early spring. Missouri Botanical Garden and Illinois: threadleaf coreopsis blooms June–September or October, a few weeks ahead of Wausau, with a fall rebloom after shearing. | Confirmed |
| Yarrow | Plant May 10–Jun 15Bloom Jul 1–Sep 15 | Iowa State: yarrow is divided in spring, every 3–4 years, and many yarrows spread rapidly; container perennials go in mid-April through May there (two to three weeks later here). Minnesota: perennials can be planted from the last week of May. Cornell: set seedlings or divisions a foot apart and divide crowded clumps in spring. Missouri Botanical Garden and Illinois: bloom June–September, and the Wildflower Center puts bloom at mid-July to mid-September in the northern US. | Confirmed |
| Feverfew | Plant May 15–Jun 15Bloom Jul 1–Sep 15 | Missouri Botanical Garden: hardy in zones 5–8, usually short-lived but persists by aggressive self-seeding; blooms June–September (about three to four weeks ahead of Wausau). NC State: zones 5–8, June–September bloom, self-seeding and can be aggressive. Iowa State and Minnesota (perennials generally): container perennials go in mid-April through May in Iowa (two to three weeks later here) and from the last week of May in Minnesota. Montana State: a trial sowed feverfew in the greenhouse Mar 30 and transplanted it May 13, and notes it is easy from transplants or direct seeding and can be grown as an annual in colder climates. | Confirmed |
| Columbine | Plant May 1–Jun 15Bloom May 20–Jun 25 | UW: blooms about a month in May and June in Wisconsin (Arboretum sheet: May–June), so roughly May 20–June 25 here; often short-lived but self-sows readily. Missouri Botanical Garden: April–May in St. Louis, about four weeks later here; Illinois: hybrids bloom May–June and last about three years. Iowa State: container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Maryland: plant perennials any time the ground is workable. | Confirmed |
| Primrose | Plant May 1–Jun 15Bloom May 5–Jun 20 | Missouri Botanical Garden: drumstick primrose (P. denticulata) blooms April–May and is rated zones 3–8, P. vulgaris blooms April (zones 4–8), and polyanthus is zones 5–7; St. Louis runs about four weeks ahead of Wausau, so bloom is roughly May 5–June 20 here. Chicago Botanic Garden: Japanese candelabra primrose blooms May–June (zones 5–7) and cowslip March–June (zones 5–8) in Glencoe, 1–2 weeks earlier than here. Iowa State: container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Illinois: most perennials are best planted in spring. | Confirmed |
| Iris | Plant May 1–Jun 15, Jul 15–Aug 31Bloom May 28–Jul 3 | UW: bearded iris can be divided any time after flowering, often in July or August in Wisconsin; Iowa State and Illinois agree (July–August) and Missouri Botanical Garden says July to early September. Siberian iris: Iowa State divides in early spring or August, Missouri Botanical Garden plants in early spring or late summer in cold-winter regions, and Minnesota says fall. Bloom: Iowa State gives tall bearded mid-May to mid-June and Siberian 1–3 weeks later in Iowa, so about May 28–July 3 here (Illinois: Siberian May–June, bearded June–July). Potted plants: Iowa State (mid-April–May in Iowa) and Illinois (spring is best), so May 1–June 15 here. | Confirmed |
| Penstemon | Plant May 1–Jun 15Bloom Jun 1–Jul 1 | UW: ‘Husker Red’ blooms about a month from mid-spring to early summer in Wisconsin, so roughly June 1–July 1 here; hardy in zones 3–8, divide in spring. Chicago Botanic Garden: May–June bloom in Glencoe, 1–2 weeks earlier than here; Missouri Botanical Garden: April–June in Missouri; Wildflower Center: May–July across the species’ range. Iowa State: container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Illinois: most perennials are best planted in spring. | Confirmed |
| Obedient Plant | Plant May 1–Jun 15Bloom Aug 1–Sep 30 | UW (Arboretum plant sheet): blooms August–October in Madison, so about August 1–September 30 here; divide clumps in early spring, and it is likely to spread more than desired. Penn State: blooms August–October, zones 3–9, spreads aggressively in moist sites; Missouri Botanical Garden: June–September in St. Louis, an aggressive spreader by rhizomes and self-seeding. Iowa State: divide in spring every 2–3 years, and container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Illinois: most perennials are best planted in spring. | Confirmed |
| Anise Hyssop | Plant May 1–Jun 15Bloom Jul 10–Sep 30 | UW: blooms from midsummer into fall (Arboretum sheet: July–September in Madison), so about July 10–September 30 here; hardy in zones 3–8, often blooms the first year from seed and self-sows readily. Missouri Botanical Garden: June–September in St. Louis (zones 4–8), about four weeks later here. Iowa State: container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Illinois: most perennials are best planted in spring. | Confirmed |
| Wild Bergamot | Plant May 1–Jun 15Bloom Jul 10–Sep 5 | UW (Arboretum plant sheet): blooms June–September in Madison, spreads by rhizomes and can be divided. Chicago Botanic Garden: in its 1993–96 trial the wild species bloomed mid-July to mid-August and had very poor powdery mildew resistance, with mildew from mid-June and full infection by late July–early August; Missouri Botanical Garden: July–September in St. Louis (and calls its mildew resistance good), so roughly July 10–September 5 here. Iowa State: container perennials go in mid-April–May in Iowa, so May 1–June 15 here; Illinois: most perennials are best planted in spring. | Confirmed |
| St. John’s Wort | Plant May 1–Jun 15Bloom Jul 5–Sep 5 | UW (Arboretum plant sheets): Kalm’s blooms late June–early October and shrubby St. John’s wort July–September in Madison, so about July 5–September 5 here; prune in early spring. Morton Arboretum: both are rated zone 4 and up and flower on new wood; Missouri Botanical Garden: Kalm’s blooms July–August (zones 4–7), shrubby June–August (zones 3–8). Iowa State: container shrubs go in from early spring through early summer (mid-March–early June in Iowa), so May 1–June 15 here; Minnesota: container-grown shrubs can be planted any time in the growing season. | Confirmed |
| Cup Plant | Plant May 1–Jun 15Bloom Jul 15–Sep 30 | UW (Prairie Primer): seedlings are usually planted in spring, small plantings by June; cup plant blooms July to October in Wisconsin. Missouri Botanical Garden: spring is the first choice for native plants, mid-March to the end of May in Missouri, so mid-April to June here; blooms July to September. Illinois: herbaceous natives can be transplanted in spring; blooms July–September. Wildflower Center: blooms July to September; the leaf cups hold water and attract birds. | Confirmed |
| Goldenrod | Plant May 1–Jun 15Bloom Aug 15–Oct 5 | UW: divide ‘Fireworks’ goldenrod clumps in early spring; it blooms in September, and Wisconsin prairie goldenrods bloom August to October (Prairie Primer). Iowa State: goldenrod divides in spring or late summer to fall; spring division is April in Iowa, late April to early May here. Missouri Botanical Garden: spring is the first choice for native plants (mid-April to June here); Canadian goldenrod blooms August to October. Illinois: goldenrod pollen is too heavy to blow about; ragweed causes the fall hay fever. | Confirmed |
| Wild Ginger | Plant Apr 20–May 20Bloom May 1–31 | UW: early spring is the best time to divide wild ginger; it can be moved at other times, but establishment is slower. Illinois: transplants go in early spring or fall, and division is best in early spring; blooms April and May in Illinois, roughly two to three weeks earlier than Wausau. Iowa State: blooms April or May in Iowa, about three weeks earlier than here. Missouri Botanical Garden: blooms April to May in Missouri, about four weeks earlier here. | Confirmed |
| Solomon’s Seal | Plant Apr 25–May 20, Aug 25–Sep 25Bloom May 15–Jun 10 | UW: dig or divide rhizomes in spring, just as new growth emerges, or in fall; P. biflorum blooms in late spring. Missouri Botanical Garden: blooms April to May in Missouri, about four weeks earlier here; spring is the first choice for native plants (mid-April to June here), September–October the second (late August to September here). Iowa State: divide many perennials in early spring (April in Iowa) or mid-August through September. | Confirmed |
| Little Bluestem | Plant May 15–Jun 25Bloom Aug 20–Oct 31 | Minnesota (Narem and Meyer): grasses can be planted from after the last spring frost to a month before the first hard freeze, and spring gives the best chance of success in zones 3 and 4; fall color is red and orange. UW: prairie seedlings are usually planted in spring; little bluestem flowers in late summer, the seed heads last over winter, and it turns copper in fall. Iowa State: ornamental grasses divide in spring or late summer to fall, and spring is better. Missouri Botanical Garden: flowers in August in Missouri (about a month later here); seed heads persist into winter. | Confirmed |
| Switchgrass | Plant May 15–Jun 25Bloom Aug 1–Oct 31 | Minnesota (Narem and Meyer): grasses can be planted from after the last spring frost, with spring best in zones 3 and 4; switchgrass is 3–6 ft, zones 3–8, and can be aggressive. UW: warm-season and zone 3, with airy flowers and seed heads; the Prairie Primer says to go easy on it in prairie mixes and to plant seedlings in spring. Iowa State: spring is better than fall for dividing ornamental grasses. Missouri Botanical Garden: flower panicles appear in mid-summer in Missouri (about a month later here) and persist into winter. | Confirmed |
| Bergenia | Plant May 10–Jun 15, Aug 20–Sep 20Bloom Apr 25–May 25 | Morton Arboretum: hardy to zone 3; pink flowers in mid-spring (about two weeks later here); cut plants back in early spring rather than fall. Illinois: blooms late winter to early spring in central Illinois (late April to May here); container perennials go in best in spring. Iowa State: plant container perennials from mid-April through May (about two weeks later here); late summer to early fall suits division. Minnesota and Penn State: divide spring bloomers in fall. | Confirmed |
| Firecracker Plant (Russelia) | Plant May 25–Jun 10Bloom Jun 15–Sep 25 | NC State: hardy in zones 9–11 and does poorly outdoors below 41°F; blooms from late spring to frost; in colder zones, grow it in pots or baskets and bring it indoors for winter. Missouri Botanical Garden: zones 9–11; in St. Louis, grow it in pots or hanging baskets and overwinter it indoors. Like the tool’s other tropicals, it goes out after the ~May 15 frost date, once nights stay warm. | Confirmed |
| Brunnera | Plant Apr 25–Jun 5, Aug 15–Sep 5Bloom May 5–Jun 5 | UW (Wisconsin Horticulture, ‘Jack Frost’): divide in early spring as growth resumes (late April here) or about six weeks before the first fall frost (about Aug 20); blooms in mid-spring for three to four weeks. Iowa State: divide in spring, or in late summer and early fall at least four to six weeks before the ground freezes. Minnesota: divide in spring, late summer, or fall, leaving four to six weeks before the ground freezes. The Morton Arboretum (April–May near Chicago) and the Missouri Botanical Garden (April–May in St. Louis) put bloom two to four weeks ahead of Wausau. | Confirmed |
| Tall Sedum | Plant May 1–Jun 15Bloom Aug 20–Oct 5 | Missouri Botanical Garden (‘Autumn Joy’): divide in spring and cut back in late spring to control height; blooms September–October in St. Louis, pink, then rose-red, then coppery rust. Iowa State: divide stonecrop in spring (late April to May here). Minnesota: divide fall bloomers in spring; interest in late summer and early fall. UW (Portage County calendar): divide summer- and fall-blooming perennials in May; Wisconsin Horticulture names ‘Autumn Joy’ an early-fall nectar plant for monarchs. NDSU: blooms August–September. | Confirmed |
| Coleus | Indoors Mar 10–Apr 5 · Plant May 25–Jun 10Leaf color Jun 1–Sep 30 | Minnesota: sow about eight weeks before planting out (its seed table allows 10–11 weeks indoors), on the soil surface, since the seed needs light; plant out once the soil passes 60°F; coleus is among the first plants hurt by cold nights. Iowa State: 8–10 weeks indoors plus one to two weeks to harden off (about Mar 9–30 for a late-May planting). Missouri Botanical Garden: start seed 8–12 weeks before the last frost, and remove the flower spikes. Cornell: sow 10 weeks before the last frost; plant only after all danger of frost. Penn State: tropicals like coleus can stay outdoors once nights hold above 50°F. Chicago Botanic Garden: very frost-sensitive; plant out after May 15 near Chicago, about two weeks later here. UW (Portage County calendar): take cuttings in mid-August and bring coleus in during September, which ends the leaf-color window. Grown for its leaves, so the tool shows a leaf-color season rather than a bloom window; the sources say to clip the flower spikes. | Confirmed |
Sources used in the cross-check
A few documents back a recommendation rather than a date, such as invasive status or toxicity; they are listed under their institution with the rest.
- UW–Madison Division of Extension (all of its pages count as one institution): A1653, Vegetable Cultivars and Planting Guide for Wisconsin Gardens · A3687, Growing Tomatoes, Peppers and Eggplants in Wisconsin · A3688, Growing Pumpkins and Other Vine Crops in Wisconsin · A3785, Growing Onions, Garlic, Leeks and Other Alliums in Wisconsin · Wisconsin Horticulture: Chives · Wisconsin Horticulture: Parsley · Wisconsin Horticulture: Zinnias · Wisconsin Horticulture: Marigolds · Wisconsin Horticulture: Peony · Swiss Chard, Wisconsin Horticulture · Cilantro / Coriander, Coriandrum sativum (Wisconsin Horticulture) · Rosemary, Salvia rosmarinus (= Rosemarinus officinalis) (Wisconsin Horticulture) · Sage, Salvia officinalis (Wisconsin Horticulture) · Fennel, Foeniculum vulgare (Wisconsin Horticulture) · German Chamomile, Matricaria chamomilla (Wisconsin Horticulture) · Monthly Gardening Guide, Extension Portage County · Storing Tender “Bulbs” for Winter · Overwintering Tender Geraniums · Aster, Symphyotrichum spp. · ‘Prairie Sun’ Black-eyed Susan, Rudbeckia hirta · Eastern red columbine (Aquilegia canadensis), Wisconsin Horticulture · Aquilegia canadensis (Wild Columbine), Friends of the Arboretum plant sheet · Dividing Bearded Iris, Wisconsin Horticulture · Iris Borer, Wisconsin Horticulture · Foxglove Beardtongue, Penstemon digitalis ‘Husker Red’, Wisconsin Horticulture · Physostegia virginiana (False Dragonhead), Friends of the Arboretum plant sheet · Anise hyssop, Agastache foeniculum, Wisconsin Horticulture · Agastache foeniculum (Lavender Hyssop), Friends of the Arboretum plant sheet · Monarda fistulosa (Bergamot), Friends of the Arboretum plant sheet · Hypericum kalmianum (St. John’s Wort), Friends of the Arboretum plant sheet · Hypericum prolificum (Shrubby St. John’s Wort), Friends of the Arboretum plant sheet · G2736, Prairie Primer (UW–Extension) · Wisconsin Horticulture: ‘Fireworks’ Goldenrod, Solidago rugosa · Wisconsin Horticulture: Wild Ginger, Asarum spp. · Wisconsin Horticulture: Solomon’s Seal, Polygonatum spp. · Wisconsin Horticulture: Gardening with Native Ornamental Grasses · Brunnera macrophylla ‘Jack Frost’, Wisconsin Horticulture · Fall Flowers Fuel Monarch Flights, Wisconsin Horticulture
- University of Minnesota Extension: Planting the vegetable garden · Upper Midwest home garden care calendar · Starting seeds indoors · Growing pumpkins and winter squash in home gardens · Growing garlic · Growing dill in home gardens · Growing chives in home gardens · Growing parsley in home gardens · Zinnia · Sunflowers · Marigolds · Growing petunias · Daylilies · Growing hostas · How and when to divide perennials · Growing lilacs · Planting and transplanting trees and shrubs · Growing kohlrabi in home gardens · Growing peppers · Growing cauliflower in home gardens · Growing Brussels sprouts in home gardens · Growing cabbage in home gardens · Growing spinach and Swiss chard in home gardens · Growing carrots and parsnips in home gardens · Growing herbs in home gardens · Planting vegetables in midsummer for fall harvest · Tuberous begonias · Begonia · Upper Midwest home garden care schedule · Planting bulbs, tubers and rhizomes · Dahlia Trial Garden, University of Minnesota Landscape Arboretum · Growing geraniums as annual flowers in Minnesota · Asters for Minnesota gardens, University of Minnesota Landscape Arboretum · How and when to divide perennials · Planting and transplanting trees and shrubs · Gardening with Native Grasses in Cold Climates, 4.1 Planting (Narem & Meyer, University of Minnesota Libraries Publishing, 2020) · Gardening with Native Grasses in Cold Climates, 3.13 Little bluestem · Gardening with Native Grasses in Cold Climates, 3.12 Switchgrass · Coleus
- Purdue Extension: HO-186-W, Indiana Vegetable Planting Calendar (counts from a one-in-ten frost date: May 21 and Sept 21 for Wausau) · Tender Perennials Need Indoor Protection
- Cornell Cooperative Extension: First Planting Dates (Tompkins County; last frost mid-May) · Last Planting Dates (Allegany County; first frost Oct 1) · Indoor Vegetable Seed Starting (Seneca County) · Vegetable Varieties for Gardeners, winter squash search (Cornell Garden-Based Learning) · Color-changing squash reveals ripeness (Cornell Chronicle) · Home Grown Facts: Harvesting and Preserving Herbs (Cornell Cooperative Extension of Oneida County; text credited to NC State Extension) · Flower Growing Guides: Tuberous Begonia (upright cultivars) · Flower Growing Guides: Begonia (wax) · Flower Growing Guides: Dahlia, medium to tall varieties · Flower Growing Guides: Pansy · Flower Growing Guides: Geranium, Common · Flower Growing Guides: Aster, New England · Flower Growing Guides: Gloriosa Daisy (Rudbeckia hirta) · Flower Growing Guides: Coreopsis, Threadleaf · Flower Growing Guides: Coreopsis, Lanceleaf · Flower Growing Guides: Yarrow · Coleus; Flame Nettle, NYS Horticulture Study Guide for Youth
- University of Illinois Extension: When to Plant · Summer Squash · Basil · Dill · Impatiens · Hort Answers: purple coneflower · Hort Answers: daylily · Hort Answers: hosta · Hort Answers: peony · Hort Answers: common lilac · Hort Answers: petunia · Hort Answers: marigold · Winter Squash, Home Vegetable Gardening · Cilantro (Herb Gardening) · Rosemary (Herb Gardening) · Harvesting Hardy Herbs (The Garden Scoop) · Thyme (Herb Gardening) · Sage (Herb Gardening) · Mint (Herb Gardening) · Tarragon: French (Herb Gardening) · Fennel (Herb Gardening) · Oregano (Herb Gardening; the page is headed Greek Oregano) · Wax Begonia, Fibrous Begonia · Tubrose Begonia · Plant of the Week: Dahlias · Pansy, Viola · Support pollinators with cheerful viola flowers · Geranium · New England Aster, Hort Answers · Black Eyed Susan (Rudbeckia fulgida) · Black Eyed Susan (Rudbeckia hirta), Hort Answers · Threadleaf Coreopsis · Tickseed · Common Yarrow · Flowers: Planting and Care (perennials) · Columbine in the garden: beauty, pollinators, and the battle with leafminers · Columbine (Aquilegia x hybrida), Flowers · How to divide and plant bearded iris, Good Growing · Bearded Iris, Flowers · Siberian Iris, Flowers · Beebalm, Flowers · Hort Answers: Cup Plant (Silphium perfoliatum) · Plant native perennials in the fall for healthy spring growth · Autumn allergies: don’t blame goldenrod (Good Growing) · Wild ginger: A native groundcover for shady gardens (Good Growing) · Plant of the Week: Pigsqueak, Bergenia
- Iowa State University Extension: Growing Basil in the Home Garden · Growing Sunflowers and Their Varieties · How to Start Petunias from Seed Indoors · Petunias · Growing Impatiens in the Home Garden · How to Divide and Transplant Perennials · When is the best time to plant peonies? · How to Plant Shrubs · Growing Brussels Sprouts in the Home Garden · Growing Carrots and Parsnips · Growing Cantaloupe, Muskmelon, and Other Melons in the Home Garden · Growing Watermelon in the Home Garden · PM 1893, Cilantro (Iowa State Horticulture Guide; copy hosted on a UW–Extension county site) · Growing, Harvesting, and Drying Herbs (Yard and Garden) · What herbs are best to grow in Iowa? (Yard and Garden) · When should I start tuberous begonias indoors? · Growing Begonias in Iowa · When should I start dahlias indoors? · Planting and Caring for Tender Perennials · Growing Pansies & Violas · Growing Annual Geraniums · This Garden is for the Birds -- Hummingbirds! · Cigar Plants Light Up Container Gardens (Reiman’s Pick, Oct. 2004) · Asters, Iowa State University Extension and Outreach Linn County · How to Plant Perennials · Transplanting and Dividing Iris, Yard and Garden · Irises for the Home Landscape, Yard and Garden · Native Woodland Wildflowers for the Home Garden · Can I start my seeds indoors yet?
- Penn State Extension: Purple Coneflower · A Guide to Dividing Perennials · Pumpkins and Winter Squash in the Garden and the Kitchen · Cilantro, a Unique Culinary Herb · Growing Herbs in the Garden · Rain Garden Plants: Obedient Plant · How Hardy Are Your Annuals? · Tropical Plants to Overwinter
- University of Maryland Extension: Starting Vegetable Seeds Indoors · Growing Peppers in a Home Garden · Growing Brussels Sprouts in a Home Garden · Growing Winter Squash in a Home Garden · Cilantro/Coriander · Care of Herbs and Starting Herbs from Seed · Rosemary · Thyme · Sage · Growing Mint in a Home Garden · Tarragon · Fennel · Oregano · Eastern Columbine · Perennials: Selection, Planting, and Care
- NDSU Extension: FN1933, Field to Fork: Cilantro · H1267, From Garden to Table: Harvesting Herbs for Healthy Eating · Annual and Perennial Flowers for North Dakota (H322)
- The Morton Arboretum: Siebold’s hosta · Kalm’s St. John’s wort (Hypericum kalmianum) · Shrubby St. John’s wort (Hypericum prolificum) · Bergenia · Siberian bugloss
- Missouri Botanical Garden: Salvia rosmarinus, Plant Finder · Thymus vulgaris, Plant Finder · Salvia officinalis, Plant Finder · Artemisia dracunculus ‘Sativa’ (French tarragon), Plant Finder · Artemisia dracunculus (tarragon), Plant Finder · Matricaria recutita (German chamomile), Plant Finder · Chamaemelum nobile (Roman chamomile), Plant Finder · Origanum vulgare subsp. hirtum (Greek oregano), Plant Finder · Origanum vulgare (oregano), Plant Finder · Begonia (Tuberosa Group), Plant Finder · Begonia (Semperflorens Cultorum Group), Plant Finder · Dahlia (group), Plant Finder · Viola × wittrockiana, Plant Finder · Pelargonium × hortorum, Plant Finder · Cuphea ignea, Plant Finder · Russelia equisetiformis, Plant Finder · Symphyotrichum novae-angliae, Plant Finder · Rudbeckia hirta, Plant Finder · Rudbeckia fulgida var. sullivantii ‘Goldsturm’, Plant Finder · Coreopsis verticillata, Plant Finder · Coreopsis lanceolata, Plant Finder · Achillea millefolium, Plant Finder · Tanacetum parthenium, Plant Finder · Aquilegia canadensis, Plant Finder · Primula denticulata ‘Lilac Globe’ (drumstick primula), Plant Finder · Primula vulgaris, Plant Finder · Primula veris (cowslip), Plant Finder · Primula (polyanthus type), Plant Finder · Iris germanica (common flag), Plant Finder · Iris ‘Caesar’s Brother’ (Siberian iris), Plant Finder · Penstemon digitalis ‘Husker Red’, Plant Finder · Physostegia virginiana, Plant Finder · Physostegia virginiana ‘Miss Manners’, Plant Finder · Agastache foeniculum, Plant Finder · Monarda fistulosa, Plant Finder · Hypericum kalmianum, Plant Finder · Hypericum prolificum, Plant Finder · Hypericum perforatum (common St. John’s wort), Plant Finder · Plant Finder: Silphium perfoliatum (cup plant) · Landscaping with Native Plants: A Gardener’s Guide for Missouri, Ch. 4 (Shaw Nature Reserve, 2011) · Plant Finder: Solidago canadensis (Canadian goldenrod) · Plant Finder: Solidago speciosa (showy goldenrod) · Plant Finder: Asarum canadense (wild ginger) · Plant Finder: Polygonatum biflorum (small Solomon’s seal) · Plant Finder: Schizachyrium scoparium (little bluestem) · Plant Finder: Panicum virgatum (switch grass) · Russelia equisetiformis, Plant Finder · Brunnera macrophylla, Plant Finder · Brunnera macrophylla ‘Jack Frost’, Plant Finder · Hylotelephium ‘Herbstfreude’ (Autumn Joy), Plant Finder · Plectranthus scutellarioides (coleus), Plant Finder
- Chicago Botanic Garden: Thymus vulgaris, Plant Finder (archived copy captured before Feb 2022) · Cuphea ‘Cupver’ (Firecracker Plant), Plant Finder · Primula japonica (Japanese candelabra primrose), Plant Finder · Primula veris (cowslip primrose), Plant Finder · Plant Evaluation Notes 26: A Garden Study of Sundrops and Evening Primroses · Penstemon digitalis ‘Husker Red’, Plant Finder · Plant Evaluation Notes 12: Monarda and Powdery Mildew Resistance · Overwintering Coleus Plants · Hylotelephium ‘Herbstfreude’, Plant Finder
- Lady Bird Johnson Wildflower Center: Symphyotrichum novae-angliae, Native Plants of North America · Rudbeckia hirta, Native Plants of North America · Coreopsis lanceolata, Native Plants of North America · Achillea millefolium, Native Plants of North America · Penstemon digitalis (foxglove beardtongue), Native Plants of North America · Native Plants of North America: Silphium perfoliatum (cup plant)
- Montana State University, Western Agricultural Research Center: Feverfew, Western Agricultural Research Center, Montana State University
- University of Missouri Extension: Pansies bring bright colors to fall
- NC State Extension: Cuphea ignea, Plant Toolbox · Tanacetum parthenium, Plant Toolbox · Russelia equisetiformis, Plant Toolbox · Brunnera macrophylla, Plant Toolbox · Hylotelephium spectabile, Plant Toolbox · Coleus scutellarioides, Plant Toolbox · Eriocapitella × hybrida (Japanese anemone), Plant Toolbox · Actaea simplex (bugbane), Plant Toolbox
- Ohio State University Extension: Perennial of the Week: New England Aster
- South Dakota State University Extension: Fall Frost Tolerance of Common Vegetables · Pumpkins, Winter Squashes and Gourds: How to Grow It
- University of New Hampshire Extension: What is the best way to start growing my own hot peppers?
- Wisconsin Department of Natural Resources: Wild parsnip (Pastinaca sativa) · Chapter NR 40, Wisconsin’s Invasive Plants List (checked: mint is not listed) · Tansy (Tanacetum vulgare), Wisconsin DNR
- USDA Agricultural Research Service: St. Johnswort (Hypericum perforatum), USDA ARS Poisonous Plant Research Laboratory · Plant Fact Sheet: Common St. Johnswort, USDA NRCS
- Invasive Plants Association of Wisconsin: IPAW’s Working List of Invasive Plants of Wisconsin
- Wisconsin Legislature (Administrative Code): Wis. Admin. Code NR 40.05(2)(b)35: wild parsnip restricted, garden vegetable form exempt · Wisconsin Administrative Code ATCP 20.01 (seed law: noxious weed seed definitions)
5. Herbs, flowers, perennials, and natives
A1653 covers vegetables only. For herbs, annual flowers, perennials, native plants, grasses, and shrubs, the timing in the tool follows the frost dates and standard Extension classifications, and each window is checked against at least two sources in section 4:
- Frost-tender annuals and herbs (basil, dill, rosemary, zinnia, marigold, petunia, impatiens, begonia, dahlia, zonal geranium, cigar plant, firecracker plant, coleus): sow or plant out after the ~May 15 anchor, with basil, impatiens, and coleus held to late May / early June because all three stall in nights below 50°F.
- Cool-season annuals and herbs (pansy, cilantro, German chamomile): sown or planted in late April and May, since they take light frost and fade in summer heat; pansy and cilantro get a second, late-summer window.
- Hardy perennials (coneflower, daylily, hosta, chives, thyme, sage, mint, French tarragon, oregano, aster, black-eyed Susan, coreopsis, yarrow, feverfew, columbine, primrose, iris, penstemon, bergenia, brunnera, tall sedum; parsley as a biennial): planted from May into mid-June, once the soil can be worked and before summer heat; chives and parsley wait for the ~May 15 frost date, as UW and Minnesota advise for transplants. Iris, coreopsis, and bergenia also get a late-summer window. Hardiness is noted per plant.
- Native wildflowers and grasses (obedient plant, anise hyssop, wild bergamot, cup plant, goldenrod, little bluestem, switchgrass): container plants set out in spring; the warm-season grasses after the last frost. Woodland natives (wild ginger, Solomon’s seal) go in from late April into May, and Solomon’s seal can also go in from late August into September. Buy nursery-propagated plants rather than wild-dug ones.
- Fall-planted perennials (peony, garlic): September–October windows, per Extension guidance that bare-root peonies and hardneck garlic establish best in fall.
- Shrubs (lilac, St. John’s wort): planted in spring, per Minnesota and Iowa State guidance for container-grown shrubs; lilac’s prune-right-after-bloom rule follows UW’s Lilacs for Cold Climates bulletin.
- Planting steps. Where a window isn’t a transplant, the calendar names what goes in: garlic cloves, seed potatoes, onion sets, and bare-root peony divisions; perennials whose sources time division to the same window say “plant or divide” (iris and Solomon’s seal by their rhizomes).
- Harvest and bloom. Vegetable and herb windows are harvests and flower windows are bloom. A harvest that comes the year after planting says so: garlic planted in October is dug the following summer, and overwintered parsnips the following spring.
- Invasiveness. Guides flag invasiveness where it matters here: Wisconsin’s invasive-species rule restricts wild parsnip but exempts the garden vegetable form, and the Wisconsin DNR treats the orange ditch lily as invasive. Toxicity has its own section, next.
Wisconsin Horticulture — Herbaceous Ornamentals and Deciduous Trees & Shrubs. University of Wisconsin–Madison Division of Extension.
https://hort.extension.wisc.edu/herbaceous-ornamentals/ · https://hort.extension.wisc.edu/deciduous-trees-shrubs/
https://hort.extension.wisc.edu/herbaceous-ornamentals/ · https://hort.extension.wisc.edu/deciduous-trees-shrubs/
6. Plant safety
Some garden plants are poisonous. The tool leaves out flowers, herbs, and native plants that a university poison reference puts in its most dangerous class, and its guides say where a plant it keeps can cause harm. All 81 plants were screened on October 3, 2026, and the five suggested on October 4 the same way, against two independent references:
NC State Extension Gardener Plant Toolbox. North Carolina State University and N.C. A&T State University Cooperative Extension. Rates a poisonous plant’s severity as Low, Medium, or High and lists its poisonous parts and symptoms.
https://plants.ces.ncsu.edu/
https://plants.ces.ncsu.edu/
Safe and Poisonous Garden Plants: Toxic Plants (by Common Name). University of California Agriculture and Natural Resources, 2020, using the California Poison Control System’s toxicity classes. Class 1, major toxicity: “These plants may cause serious illness or death.”
https://ucanr.edu/sites/default/files/2022-02/363609.pdf
https://ucanr.edu/sites/default/files/2022-02/363609.pdf
The rule. A flower, herb, or native plant that NC State rates High or UC rates Class 1 stays out of the tool; either rating is enough. Vegetables are the exception, because the part you eat is safe, and their guides name the parts that aren’t. Every plant the tool keeps that NC State rates Medium or higher, or UC rates Class 1, carries a Safety line in its guide.
| Plant | NC State | UC | In the tool |
|---|---|---|---|
| Removed October 3, 2026 | |||
| Datura (D. inoxia, D. metel) | High | Not listed | Removed. UW–Madison Extension: its alkaloids are “toxic, narcotic and hallucinogenic,” and eating it can cause serious illness or death. |
| Nicotiana (N. alata, N. sylvestris) | High for N. sylvestris (nicotine-like alkaloids); N. alata not rated | Class 1 for flowering tobacco, N. glauca | Removed |
| Mayapple | High | Class 1 | Removed. Everything but the ripe fruit is poisonous. |
| Bloodroot | High (root) | Not listed | Removed |
| Wild lupine | Low (seeds) | Class 1 for all lupines | Removed. The references disagree; under the rule, either top rating is enough. |
| Not added, October 4, 2026 | |||
| Bugbane (Actaea simplex, A. racemosa) | High for A. simplex and the genus (cardiotoxic; it “can cause death in humans”) | Not listed | Not added |
| Japanese anemone (Anemone × hybrida) | High on its current page (Eriocapitella × hybrida); Medium for the genus and for ‘September Charm’; Low for Chinese anemone, A. hupehensis | Classes 2 and 4 for Anemone spp. (minor toxicity, dermatitis) | Not added. NC State’s pages disagree; under the rule, its top rating is enough. |
| Kept, with a Safety line | |||
| Potatoes | High | Class 1 (green parts) | Leaves, stems, berries, sprouts, and green skin are poisonous; Minnesota Extension says to cut away green areas and sprouts and to store potatoes in the dark. |
| Tomato | Medium (leaves and stems) | Class 1 (leaves and stems) | Only the fruit is food. NC State notes that reported poisonings are rare. |
| Green beans | Medium (raw or undercooked dry beans) | Not listed | Cook dry beans thoroughly. |
| Parsnips | Medium | Not listed | The sap makes skin sensitive to sunlight, causing burns and blisters; wear gloves and long sleeves. |
| Wild ginger | Medium | Not listed | Contains aristolochic acid, which damages the kidneys and can cause cancer; don’t eat any part. |
| St. John’s wort (H. kalmianum, H. prolificum) | Medium for H. prolificum; H. kalmianum not rated | Not listed (its Class 1 entry is a different species, H. calycinum) | The sap can make skin sensitive to sunlight in some people; wear gloves when pruning. |
| Daylily | No rating for people; toxic to cats | Not listed | Toxic to cats. The FDA warns that a little leaf or petal, pollen licked from fur, or water from a vase can cause fatal kidney failure. |
Everything else. NC State rates 20 of the remaining plants Low (lettuce, spinach, carrots, radishes, onions, garlic, parsley, mint, French tarragon, German chamomile, marigold, begonia, dahlia, zonal geranium, feverfew, primrose, iris, Solomon’s seal, tall sedum, and coleus) and gives the rest no poison rating; none is in UC’s Class 1. Plants in these lower groups can still cause mild stomach upset or skin irritation, and the hot pepper, fennel, and feverfew guides note handling precautions. Many common garden plants can also make pets sick; NC State’s toolbox flags the ones that are a problem for cats, dogs, or horses. If someone eats part of a plant and you’re worried, call Poison Control at 1-800-222-1222.
Also cited: UW–Madison Division of Extension, Wisconsin Horticulture, Datura; U.S. Food and Drug Administration, Lovely Lilies and Curious Cats: A Dangerous Combination; University of Minnesota Extension, Growing potatoes.
https://hort.extension.wisc.edu/articles/datura/ · https://www.fda.gov/animal-veterinary/animal-health-literacy/lovely-lilies-and-curious-cats-dangerous-combination · https://extension.umn.edu/vegetables/growing-potatoes
https://hort.extension.wisc.edu/articles/datura/ · https://www.fda.gov/animal-veterinary/animal-health-literacy/lovely-lilies-and-curious-cats-dangerous-combination · https://extension.umn.edu/vegetables/growing-potatoes
7. Monthly task list
The “This month in the garden” checklist is written by Wausau Pilot & Review from the planting windows above and the frost normals — for example, September’s “watch nighttime lows” item exists because NOAA’s one-in-ten early-frost date is September 21. It is seasonal guidance, not a substitute for the forecast.
8. Accuracy reviews
October 4, 2026: three plants added
Plant list expanded with suggestions from the North Central Wisconsin Master Gardeners Association. Brunnera, tall sedum, and coleus (an annual here, shown with a leaf-color season rather than a bloom window) cleared the same two-source check before they went in (section 4) and were screened for safety (section 6). Not added: bugbane and Japanese anemone, which NC State rates High. The tool now covers 79 plants.
October 3, 2026: plant safety review
Datura should not have been added: it is highly poisonous and hallucinogenic. We removed it and screened all 81 plants against NC State Extension’s and the University of California’s poison ratings (section 6). Four more came out under the same rule: nicotiana, mayapple, bloodroot, and wild lupine. Seven guides gained a Safety line: potatoes, tomato, green beans, parsnips, wild ginger, St. John’s wort, and daylily (for cats); the parsnip and wild ginger warnings moved there from the tips. The tool now covers 76 plants.
September 29, 2026: 50 plants added
Plant list expanded with suggestions from the North Central Wisconsin Master Gardeners Association. The dates and growing details were compiled by Wausau Pilot & Review from the sources in section 4, and every window cleared the same two-source check before it went in. The tool now covers 81 plants:
- Vegetables (10) — kohlrabi, hot pepper, cauliflower, Brussels sprouts, cabbage, Swiss chard, parsnips, winter squash, cantaloupe, and watermelon. The zucchini guide now covers all summer squash: yellow crookneck, straightneck, and pattypan share its schedule, per UW, Cornell, and Illinois.
- Herbs (9) — cilantro, rosemary, thyme, sage, mint, French tarragon, fennel, German chamomile, and oregano.
- Flowers, perennials, grasses, and shrubs (31) — begonia, dahlia, pansy, zonal geranium, nicotiana, datura, firecracker plant (Russelia), cigar plant (Cuphea), aster, black-eyed Susan, coreopsis, yarrow, feverfew, wild lupine, columbine, primrose, iris, penstemon, obedient plant, anise hyssop, wild bergamot, St. John’s wort, cup plant, goldenrod, mayapple, bloodroot, wild ginger, Solomon’s seal, little bluestem, switchgrass, and bergenia.
Not added. Chayote needs a long, frost-free season and flowers only late in it (LSU AgCenter; University of Hawaiʻi), so it cannot set fruit before frost here. ‘Stella de Oro’ is a daylily, already covered by the daylily guide. The association confirmed that “Begins” meant bergenia and that “firecracker plant” meant Russelia; cigar plant (Cuphea), which is also sold under that name, stays in as well.
Where the evidence is thinnest. A few windows rest on general guidance rather than plant-specific dates: spring planting of container perennials for several natives, the plant-out dates for cigar plant and firecracker plant (inferred from their frost tenderness), feverfew (no Upper Midwest Extension page; rated to zone 5), and bloom dates for the woodland wildflowers, converted from descriptions such as “early spring.” Each row in section 4 says what its sources actually say.
September 25, 2026: multi-source cross-check
Every planting, harvest, and bloom window was checked against at least two independent institutions (section 4), and all 31 plants are now confirmed. Four plants changed:
- Spinach — fall sowing moved from Aug 15–Sep 1 to Aug 1–15 (Minnesota: early August; Cornell: last fall sowing Aug 10 with an Oct 1 frost), so the fall harvest now starts Sep 10. The April 15 spring sowing, the one date our September 9 review left open, is supported by Minnesota, Cornell, and Purdue, so that flag is closed.
- Kale — sowing moved from May 1–Jul 15 to Apr 20–Jul 10 (Minnesota: mid-April to early July; Cornell and Purdue: mid-April). The old window also couldn’t produce the June 15 first harvest with kale’s 55–65 days.
- Chives — planting moved from Apr 20–May 20 to May 15–Jun 10: UW and Minnesota both say to plant after the danger of frost has passed.
- Hosta — the calendar bar now shows bloom (Jul 1–Aug 31) instead of the whole leaf season (Jun 1–Sep 20), which read as a bloom period.
The same pass corrected NOAA frost figures on this page to the values in NCEI’s station file. The earlier version listed Apr 22 and May 23 for the spring 90% and 10% dates; Sep 20, Oct 2, and Oct 15 for fall; 147 and 169 days for the season lengths; and Oct 13 for the 28°F fall date. The tool’s own ~May 15 and ~Oct 1 dates did not change, but it now calls them its last- and first-frost dates rather than averages, since NOAA’s medians are May 6 and Oct 4. We also added NOAA’s 36°F figures, an independent frost-date check from the Wisconsin State Climatology Office, and hardiness zones by ZIP code.
September 9, 2026: field-by-field review
We first checked every field of all 31 entries and the monthly task list — botanical names, spacing, days to harvest, water, each planting window, and every factual claim in the descriptions and tips — was compared against UW–Madison Extension, University of Minnesota Extension (the same climate band), other land-grant Extension pages, and, for varietal details, seed-house references. Of roughly 250 checked claims, the large majority were confirmed outright or consistent with Extension guidance. We corrected the following:
- Garlic — mulch depth was 4–6 inches; UW, UMN, and UW–Bayfield all say 3–4 inches. Harvest cue changed from a folk rule (“bottom three leaves brown”) to Extension’s “about half the leaves still green.” Softened a claim that all softneck garlic winterkills (some softnecks are cold-suited; grocery-store California types are the problem).
- Hosta — removed the crushed-eggshell slug remedy (it doesn’t work; UW recommends night patrols, beer traps, or iron-phosphate bait) and added deer as the other real pest; hardiness now “zone 3 or 4 depending on variety.”
- Daylily — corrected the cultivar name to ‘Stella de Oro’; replaced a recommendation of orange “ditch lilies” with a warning that the Wisconsin DNR treats Hemerocallis fulva as an invasive plant (not regulated under NR 40).
- Basil and impatiens — cold thresholds raised from 45°F/40°F to 50°F per Illinois, Minnesota, and Michigan State Extension; impatiens now steers readers to downy-mildew-resistant series (Beacon, Imara XDR) or New Guinea types, per UW Extension.
- Purple coneflower — described as Midwest-native rather than a Wisconsin native (BONAP maps Wisconsin’s E. purpurea populations as adventive — native to North America but outside its original range here; Wisconsin’s own coneflower is E. pallida, a state-threatened prairie species).
- Marigold — “pest-discouraging” replaced with the documented deer and rabbit resistance; days-to-bloom corrected upward.
- Tomato — Celebrity is a mid-season variety, not short-season; indoor start moved to April 10–25 (Extension recommends 4–6 weeks before transplanting, not 8–9).
- Parsley — indoor start moved two weeks earlier (March 10–25) because UW recommends 8–10 weeks before last frost for a seed that takes 2–5 weeks to germinate.
- Smaller tightenings — onion curing 2–4 weeks; carrot germination 2–3 weeks; kale’s “starch to sugar” wording replaced with the documented cold-raises-sugar effect; chives hardiness and shearing height; sunflower days-to-bloom range; lilac pruning timed to right after flowering per UW A3825; pepper seed-start anchored to the transplant date; pea frost tolerance qualified for flowering plants; broccoli and kale botanical names aligned with Extension usage; the February task list now excludes spring-flowering shrubs from dormant pruning; September no longer says to plant garlic (the garlic guide correctly says October).
Second pass (same day). Two further independent checks were run on the corrected data: a re-verification of every number and date (about 190 fields) against Wisconsin Horticulture articles and the UW bulletins listed below, and a regression check of each first-pass correction. No outright errors remained, but two of our own corrections were imperfect and have been fixed: the daylily note now says the Wisconsin DNR treats orange daylily as invasive but does not regulate it under NR 40 (the earlier “listed as invasive” could be read as an NR 40 listing), and lilac pruning advice now matches UW’s Lilacs for Cold Climates (“immediately after flowering”) rather than a “within 2 weeks” phrasing that isn’t UW’s. The same pass fixed internal inconsistencies (pepper seed-start math, zinnia bloom bar vs. its own days-to-bloom, marigold sowing vs. the 65°F soil rule) and tightened numbers to Extension figures: tomato hardening 10–14 days, pepper 60–70 days to green fruit, cucumber 45–60 days, bush-bean spacing 2–4 inches, lettuce 40–60 days (30 for baby leaf), onion sets 3–4 inches, pumpkin spacing stated as in-row and between-row, corn water 1 inch per week, chives 12–18 inches and division every 2–4 years.
Two of the three calendar flags were resolved with Wisconsin’s own bulletins rather than an inference: bell pepper transplanting moved to June 5–15 (A3687: “northern growers should wait 2 weeks” beyond the June 1 southern date) and cucumber sowing to June 1–20 (A3688: “not before May 27 in southern Wisconsin… delay planting an additional 1–2 weeks” in the north). The first spinach sowing (April 15) stayed open until the September 25 cross-check above confirmed it.
UW–Extension bulletins used in the second pass: A3687 Growing Tomatoes, Peppers and Eggplants in Wisconsin; A3688 Growing Pumpkins and Other Vine Crops in Wisconsin; A3785 Growing Onions, Garlic, Leeks and Other Alliums in Wisconsin (Delahaut & Newenhouse); A3825 Lilacs for Cold Climates (Jull); A2801 Growing Vegetables at Home — Questions and Answers.
https://hort.extension.wisc.edu/files/2014/11/A3687.pdf · https://barron.extension.wisc.edu/files/2023/02/Growing-Pumpkins-and-other-Vine-Crops-in-Wisconsin.pdf · https://hort.extension.wisc.edu/files/2023/10/A3785-Growing-Onions-Garlic-Leeks-and-Other-Alliums-in-Wisconsin-KA-Delahaut-and-AC-Newenhouse.pdf · https://barron.extension.wisc.edu/files/2023/02/Lilacs-for-Cold-Climates.pdf
https://hort.extension.wisc.edu/files/2014/11/A3687.pdf · https://barron.extension.wisc.edu/files/2023/02/Growing-Pumpkins-and-other-Vine-Crops-in-Wisconsin.pdf · https://hort.extension.wisc.edu/files/2023/10/A3785-Growing-Onions-Garlic-Leeks-and-Other-Alliums-in-Wisconsin-KA-Delahaut-and-AC-Newenhouse.pdf · https://barron.extension.wisc.edu/files/2023/02/Lilacs-for-Cold-Climates.pdf
9. Standards and corrections
Our standard. Every date in the tool must be supported by at least two independent published sources before it appears, and the table in section 4 shows which ones. No plant goes in that fails the safety rule in section 6. The guides are compiled by Wausau Pilot & Review. They are not reviewed or endorsed by UW–Madison Extension, the Master Gardener Program, the North Central Wisconsin Master Gardeners Association, or any other source cited here, and the tool’s timing choices, such as planning around ~May 15, are ours.
Adding plants. Plant list expanded with suggestions from the North Central Wisconsin Master Gardeners Association. More suggestions are welcome at editor@wausaupilotandreview.com; a new plant goes in only after each of its windows clears the same two-source check and it passes the safety screen in section 6.
What the tool does not do. It does not tailor dates to individual yards, account for the current year’s weather beyond the 7-day forecast, or cover pests, diseases, or soil testing. For those, the Extension resources above and the Ask Your Gardening Question service are the right place.
Corrections. If a date, variety, or tip looks wrong, email editor@wausaupilotandreview.com. Corrections are logged in section 8 with the date they were made.
Code and data. The tool is a single open-source file; the plant database, frost anchors, and forecast code can be inspected at github.com/RowanFlynnPilot/wausau-grower.