What does USDA hardiness zone 4a mean in Wisconsin?

Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 26 locations in Wisconsin fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Wisconsin's zone 4a is the growing season longest?

Haugen runs the longest season on this page at about 152 days; Oliver is shortest at about 113 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in Wisconsin's zone 4a?

Using Drummond's frost dates (this page's median-season location): start seeds indoors about Mar 25 – Apr 8, then transplant outside about May 27 – Jun 3. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Wisconsin's zone 4a have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 26 locations listed (see the table above for each location's own dates).

USDA zone 4a in Wisconsin

−30 to −25 °F avg. annual extreme minimum · 26 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4a covers 26 locations across Wisconsin (average annual extreme minimum −30 to −25 °F): Birchwood, WI, Catawba, WI, Clam Lake, WI, Drummond, WI, Exeland, WI, Gilman, WI, and 20 more. Average last spring frost across this group ranges May 5 (Haugen) to June 1 (Oliver), and growing seasons run 113–152 days (Oliver to Haugen) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Wisconsin location's own frost dates; the printable planting calendar uses Drummond, this group's median-season location.

USDA zone: 4a−30 to −25 °F
Last frost range: May 5–Jun 1avg, 32°F
First frost range: Sep 21–Oct 4avg, 32°F
Growing season range: 113–152days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Birchwood	—	Rice Lake	May 8	Oct 2	145
Catawba	Ogema, Prentice	Prentice #2	May 23	Sep 23	124
Clam Lake	—	Clam Lake 4w	May 16	Sep 30	136
Drummond *	—	Drummond	May 20	Oct 1	132
Exeland	Winter, Radisson	Winter	May 19	Sep 27	129
Gilman	Hawkins, Kennan, Jump River	Jump Rvr 3e	May 20	Sep 23	125
Glidden	Butternut	Butternut 3sw	May 22	Sep 24	126
Gordon	Solon Springs, Minong	Gordon	May 22	Sep 26	126
Haugen	—	Cumberland	May 5	Oct 4	152
Iron Belt	Pence	Hurley	May 24	Sep 28	128
Lac du Flambeau	Sayner, Lake Tomahawk, Boulder Junction, Minocqua	Minocqua	May 23	Sep 27	127
Ladysmith	Tony, Ingram	Big Falls Hydro	May 7	Oct 3	147
Lake Nebagamon	Poplar, Iron River, Brule	Brule Rs	May 24	Sep 26	124
Lublin	—	Owen 1e	May 13	Sep 26	136
Mellen	—	Mellen 4 Ne	May 26	Sep 27	125
Mercer	Boulder Junction	Rest Lake	May 25	Sep 21	117
Oliver	Wrenshall, Kerrick	Foxboro	Jun 1	Sep 22	113
Park Falls	Phillips	Park Falls Dnr Hq	May 15	Sep 28	134
Reserve	Little Round Lake, Cable	Hayward Muni Ap	May 23	Sep 22	122
Rib Lake	Whittlesey, Chelsea	Medford	May 11	Oct 1	141
Shell Lake	Spooner, Siren, Trego, Birchwood	Spooner Ag Res Stn	May 14	Sep 28	135
Stone Lake	Springbrook	Hayward Rs	May 22	Sep 23	124
Tomahawk	—	Rice Rsvr Tomahawk-2	May 10	Oct 4	146
Tomahawk	Lake Tomahawk, Minocqua	Willow Rsvr	May 13	Oct 3	141
Webster	Danbury	Danbury	May 11	Sep 30	138
Weyerhaeuser	—	Weyerhaeuser 1n	May 9	Sep 29	140

* Drummond is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Drummond, representative)

Computed from Drummond's average frost dates — the median-season location in this Wisconsinzone 4a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Drummond (Wisconsin, zone 4a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 25 – Apr 8	May 27 – Jun 3	Jul 26 – Aug 15	—	matures comfortably
Pepper	Very tender	Mar 11 – Mar 25	Jun 3 – Jun 10	Aug 2 – Sep 1	—	matures comfortably
Cucumber	Tender	Apr 22 – Apr 29	May 27 – Jun 3	Jul 16 – Aug 5	—	matures comfortably
Summer squash / zucchini	Tender	—	May 27 – Jun 3	Jul 11 – Jul 26	—	matures comfortably
Bush bean	Tender	—	May 27 – Jun 3	Jul 16 – Jul 26	Aug 2 – Aug 12	matures comfortably
Sweet corn	Tender	—	May 20 – Jun 3	Jul 19 – Aug 18	—	matures comfortably
Basil	Very tender	Apr 8 – Apr 22	May 27 – Jun 3	Jun 26 – Jul 11	—	matures comfortably
Lettuce	Half-hardy	Apr 8 – Apr 22	Apr 22 – May 6	Jun 6 – Jun 21	Jul 19 – Aug 3	matures comfortably
Pea	Hardy	—	Apr 8 – Apr 22	Jun 2 – Jun 17	Jul 9 – Jul 24	matures comfortably
Spinach	Hardy	—	Apr 8 – Apr 22	May 18 – May 28	Jul 29 – Aug 8	matures comfortably
Carrot	Half-hardy	—	Apr 29 – May 6	Jun 28 – Jul 18	Jun 29 – Jul 19	matures comfortably
Broccoli	Half-hardy	Mar 25 – Apr 8	Apr 22 – May 6	Jun 16 – Jul 6	Jul 4 – Jul 24	matures comfortably

Which crops fit this growing season

Using Drummond's own 132-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Drummond)

From NOAA's 1991–2020 Climate Normals at station USC00472240. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Drummond.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 1	Jun 14	Sep 22	Oct 4	110
32°F (freeze)	May 20	Jun 2	Oct 1	Oct 13	132
28°F	May 7	May 23	Oct 11	Oct 26	156
24°F	Apr 27	May 12	Oct 23	Nov 7	177

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 26 locations is 1,875; Drummond's own reading is shown below.

Annual growing degree days for Drummond (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,828	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,518	cool-season crops (brassicas, greens)

Hardiness zone 4a in Wisconsin

Zone 4a means an average annual extreme minimum winter temperature of about −30 to −25 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Wisconsin spans 5 hardiness zones in this dataset — see all Wisconsin locations for the full range, including zones4b, 5a, 5b, 6a.

Explore zone 4a in other states at zone 4a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 4a mean in Wisconsin?: Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 26 locations in Wisconsin fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Wisconsin's zone 4a is the growing season longest?: Haugen runs the longest season on this page at about 152 days; Oliver is shortest at about 113 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in Wisconsin's zone 4a?: Using Drummond's frost dates (this page's median-season location): start seeds indoors about Mar 25 – Apr 8, then transplant outside about May 27 – Jun 3. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Wisconsin's zone 4a have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 26 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.