Jefferson County, in Wisconsin, sits in USDA hardiness zone 5b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Reliable performers under these conditions include cranberry, cherry, potato, and ginseng; what your own ground favors still comes down to its soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Jefferson County holds more than one microclimate.
Soils and elevations shift across Jefferson 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
5b
Last Hard Freeze (28°F)
Apr 7
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Nov 9
County normal — light frosts arrive a few weeks earlier
County Area
356K acres
Hardiness Zone Range
Zone maps are averages across Jefferson County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Jefferson County
Across Jefferson County, the ground is predominantly Alfisols, where Kidder, Houghton, and Fox are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 6.5–7.0, neutral. Rainfall drains through hydrologic group B/D soils.
Soil order
Alfisols
Drainage
Well drained
Prime farmland
26%
Hydric soils
34%
Soil still varies lot by lot — soil types explained.
What Grows in Jefferson County
Plants matched to Jefferson County's USDA zones 5b — each links to its full growing profile.
Is it too late to plant in Jefferson County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 10; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 9 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
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 Jefferson County — and how to grow with it.
We checked the federal record across Jefferson County — 860 documented sites across 7 of the 9 source types we track.
The most significant on record: 9 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Jefferson County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
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 Jefferson County
Severity Distribution
across Jefferson County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Jefferson County, two things run higher than the national average — CAFO (11 sites) and Toxic Release Inventory (55 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Toxic Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Check your specific parcel in Jefferson 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
Jefferson County Average
- ●USDA Zones 5b
- ●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 Jefferson County
Pull a site-specific report for your exact address in Jefferson 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 Jefferson County, Wisconsin
- USDA Hardiness Zones: 5b (USDA PHZM 2023)
- Last Hard Freeze (28°F): Apr 7 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Nov 9 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~216 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 356K 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 Jefferson 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 Jefferson County, Wisconsin?
Jefferson County sits in USDA hardiness zone 5b, 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 Jefferson County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 10; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 9 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
When does frost risk typically end in Jefferson County?
The last hard freeze (28°F) in Jefferson County typically lands around Apr 7, 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 Jefferson County?
Measured between 28°F hard freezes, Jefferson County sees about 216 frost-free days — roughly Apr 7 through Nov 9, 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 Jefferson County?
Jefferson County's zone 5b 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 Jefferson County, really?
Officially, Jefferson County sits in USDA zone 5b (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 Jefferson County?
The federal record around Jefferson County runs heavier than most — 860 documented sites — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
Just moved to Jefferson County — what should I know before planting?
Start with three facts. Jefferson County sits in USDA zone 5b, which sets what survives winter; the last 28°F hard freeze typically clears around Apr 7, with about 216 frost-free days to work with (NOAA 1991–2020 climate normals); and 860 documented sites sit on the federal record here, so a soil test before food beds is the smart first step. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a Jefferson 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.