Mahnomen County, in Minnesota, sits in USDA hardiness zone 4a — a zone band wide enough that plant choice, not possibility, is the interesting question.
Growers here do well with honeycrisp apple, wild rice, tomato, and red pine — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Mahnomen County holds more than one microclimate.
Soils and elevations shift across Mahnomen 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.
No card required · your full report in seconds
Quick Facts
USDA Zones
4a
Last Hard Freeze (28°F)
Apr 22
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Oct 22
County normal — light frosts arrive a few weeks earlier
County Area
357K acres
Hardiness Zone Range
Zone maps are averages across Mahnomen County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Mahnomen County
Across Mahnomen County, the ground is predominantly Mollisols, where Vallers, Hamerly, and Waukon are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.5–7.6, neutral. Rainfall drains through hydrologic group C/D soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
30%
Hydric soils
36%
Soil still varies lot by lot — soil types explained.
What Grows in Mahnomen County
Plants matched to Mahnomen County's USDA zones 4a — each links to its full growing profile.
Is it too late to plant in Mahnomen County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 25; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 22 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 22 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
Growing Challenges in Minnesota
What an experienced grower plans around here — each one has a move.
Extreme cold (zone 3a: -40F) limits many species
Plant to zone 3 realities and the garden thrives — the hardy-plant palette here is deeper than most catalogs suggest.
Short growing season (100-140 frost-free days)
Start transplants indoors and add a cold frame — the standard Minnesota moves that stretch a short season into a full one.
Heavy clay soils in the Red River Valley
Valley clay grows world-class crops once drainage is handled — raised beds do it instantly, compost does it permanently.
For cultivar selection, pest pressure, and planting-time guidance specific to Minnesota, the University of Minnesota Extension is the authoritative local source.
Safe to Grow Here?
What the federal record shows across Mahnomen County — and how to grow with it.
We checked the federal record across Mahnomen County — 71 documented sites across 3 of the 9 source types we track.
The most significant on record: 16 brownfield sites. Former commercial or industrial land where legacy contamination may persist.
The federal record across Mahnomen 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.
Severity Distribution
across Mahnomen County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Mahnomen County, Nitrate runs higher than the national average — 26 sites nearby. That's not a problem with your land — it's information about it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Mahnomen 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
Mahnomen 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 Mahnomen County
Pull a site-specific report for your exact address in Mahnomen County, Minnesota — 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 Mahnomen County, Minnesota
- USDA Hardiness Zones: 4a (USDA PHZM 2023)
- Last Hard Freeze (28°F): Apr 22 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Oct 22 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~183 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 357K 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 Mahnomen 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 Mahnomen County, Minnesota?
Mahnomen 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 Mahnomen County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 25; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 22 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 22 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
When does frost risk typically end in Mahnomen County?
The last hard freeze (28°F) in Mahnomen County typically lands around Apr 22, 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 Mahnomen County?
Measured between 28°F hard freezes, Mahnomen County sees about 183 frost-free days — roughly Apr 22 through Oct 22, 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 Mahnomen County?
Mahnomen County's zone 4a supports a wide range — strong performers include Honeycrisp Apple, Wild Rice, Tomato, and Red Pine. 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 Mahnomen County, really?
Officially, Mahnomen 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 Mahnomen County?
The federal record around Mahnomen County shows 71 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 Mahnomen County — what should I know before planting?
Start with three facts. Mahnomen County sits in USDA zone 4a, which sets what survives winter; the last 28°F hard freeze typically clears around Apr 22, with about 183 frost-free days to work with (NOAA 1991–2020 climate normals); and 71 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 Mahnomen 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 Minnesota's frost window, season length, and soil profile against the plant's real requirements.