Iron County, in Wisconsin, sits in USDA hardiness zone 4a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Expect cranberry, cherry, potato, and ginseng to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Iron County holds more than one microclimate.
Soils and elevations shift across Iron County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,112 plants against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Quick Facts
USDA Zones
4a
Last Hard Freeze (28°F)
Apr 29
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Oct 20
County normal — light frosts arrive a few weeks earlier
County Area
485K acres
Hardiness Zone Range
Zone maps are averages across Iron County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Iron County
Across Iron County, the ground is predominantly Spodosols, where Gogebic, Pence, and Lupton are the most extensive named soil series. The soil is generally moderately well drained with a fine sandy loam surface. Topsoil pH runs about 4.2–5.5, very strongly acidic. Rainfall drains through hydrologic group D soils.
Soil order
Spodosols
Drainage
Moderately well drained
Prime farmland
3%
Hydric soils
35%
Soil still varies lot by lot — soil types explained.
What Grows in Iron County
Plants matched to Iron County's USDA zones 4a — each links to its full growing profile.
Is it too late to plant in Iron County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Apr 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 29 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 20 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
Growing Challenges in Wisconsin
What an experienced grower plans around here — each one has a move.
Cold winters (-30F in northern WI)
Plant perennials rated for the cold you actually get — northern Wisconsin rewards zone honesty with decades of returns.
Short growing season (110-140 frost-free days)
Indoor starts plus a cold frame stretch the season on both ends — standard practice from Madison to Superior.
Sandy central soils drain too quickly
The Central Sands fix is organic matter — compost and cover crops, every year, until the ground holds its own water.
For cultivar selection, pest pressure, and planting-time guidance specific to Wisconsin, the UW–Madison Division of Extension is the authoritative local source.
Safe to Grow Here?
What the federal record shows across Iron County — and how to grow with it.
We checked the federal record across Iron County — 171 documented sites across 4 of the 9 source types we track.
The most significant on record: 37 brownfield sites. Former commercial or industrial land where legacy contamination may persist.
The federal record across Iron County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Environmental Intelligence
Understanding what's nearby helps you make informed decisions about where and how to grow.
Sources Checked
across Iron County
Severity Distribution
across Iron County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Iron County, Underground Storage Tanks runs higher than the national average — 119 sites nearby. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Iron County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,112 plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Your Specific Parcel Matters
Iron County Average
- ●USDA Zones 4a
- ●Generic soil type for the area
- ●State-average frost dates
YOUR Parcel
- ✓Your exact hardiness zone
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Iron County
Pull a site-specific report for your exact address in Iron County, Wisconsin — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Key Growing Facts for Iron County, Wisconsin
- USDA Hardiness Zones: 4a (USDA PHZM 2023)
- Last Hard Freeze (28°F): Apr 29 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Oct 20 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~174 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 485K acres (US Census TIGER 2025)
Zone data: USDA ARS Plant Hardiness Zone Map 2023. Climate data: NOAA NCEI. County boundaries: US Census TIGER/Line 2025.
Frost dates here are the Iron County average. Low spots and tree cover move them by days on any one yard — see your exact frost windows.
Frequently Asked Questions
What hardiness zone is Iron County, Wisconsin?
Iron County sits in USDA hardiness zone 4a, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.
Is it too late to plant in Iron County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Apr 1; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 29 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 20 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
When does frost risk typically end in Iron County?
The last hard freeze (28°F) in Iron County typically lands around Apr 29, per NOAA 1991–2020 climate normals — an earlier marker than the light-frost dates many planting charts quote. That marks the hard freeze, not the last light frost — light frosts can still bite for a few more weeks, so tender transplants usually wait another 2–3 weeks.
How long is the growing season in Iron County?
Measured between 28°F hard freezes, Iron County sees about 174 frost-free days — roughly Apr 29 through Oct 20, per NOAA 1991–2020 climate normals. Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.
What vegetables grow in Iron County?
Iron County's zone 4a supports a wide range — strong performers include Cranberry, Cherry, Potato, Ginseng, and Sugar Maple. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.
Which hardiness zone is Iron County, really?
Officially, Iron County sits in USDA zone 4a (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.
Is the soil safe to grow vegetables in Iron County?
The federal record around Iron County shows 171 documented sites — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Just moved to Iron County — what should I know before planting?
Start with three facts. Iron County sits in USDA zone 4a, which sets what survives winter; the last 28°F hard freeze typically clears around Apr 29, with about 174 frost-free days to work with (NOAA 1991–2020 climate normals); and 171 documented sites sit on the federal record — a typical footprint for a growing area, worth a look on the contamination map before food beds. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a Iron County average. Your yard writes its own version — we read soil, sun, drainage, and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Wisconsin's frost window, season length, and soil profile against the plant's real requirements.