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 cabbage, cranberry, turkish rocket, and collard greens — 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 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Mahnomen County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Mahnomen County — the short answer
Mahnomen County, Minnesota: USDA zone 4a, about 162 days between hard freezes, across 357K acres.
- USDA zone
- 4a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 30
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 9
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~162
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 357K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 4a is Mahnomen County's average, not your lot's — a low corner or a tree line moves it. Against Mahnomen County's 162-day season, see what your own ground reads.
Heat in Mahnomen County
Across a year, Mahnomen County accumulates about 1,859 growing degree days above 50°F, about 406 fewer than the middle Minnesota county — ahead of 19 of Minnesota’s 87 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
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.
How the ground varies across Mahnomen County
The USDA soil survey maps 35% of Mahnomen County as well drained — but another 61% drains differently: 19% poorly drained, 14% somewhat poorly drained.
Vallers is the most extensive named soil at 12% of mapped acres, then Hamerly (10%) and Waukon (7%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Mahnomen County
Each reading below is measured for Mahnomen County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Mahnomen County are well drained, in hydrologic group C/D — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Mahnomen County runs about pH 6.5–7.6, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Wet ground
MeasuredAbout 36% of Mahnomen County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredMahnomen County runs about 162 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
The kind of country Mahnomen County is in
Mahnomen County spans 3 EPA Level III ecoregions — Lake Agassiz Plain (46%), North Central Hardwood Forests (39%) and Northern Lakes and Forests (16%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Mahnomen County
We scored all 1,086 plants against Mahnomen County's own USDA zone 4a and its own 162-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Minnesota 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 Apr 2; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 30 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 9 — 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.
What gets applied to farmland in Mahnomen County
USGS estimates 89,584 lb of Glyphosate on Mahnomen County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (12,467 lb) and Dicamba (10,256 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
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.
What's on the federal record near Mahnomen County
Closest first, across Mahnomen County. Listing isn't leaking, and distance isn't exposure.
- Roy Lake StoreUnderground Storage Tanks · 1.0 mi
- 145N40W15CDA 01 A ScheffNitrate · 1.2 mi
- Dept Of Natural Resources/forestryUnderground Storage Tanks · 2.6 mi
- Roy Lake LodgeUnderground Storage Tanks · 2.6 mi
- Pump 24 C-storeUnderground Storage Tanks · 2.6 mi
- Jacks Motor SportUnderground Storage Tanks · 2.6 mi
- Eids 59 Midway ServiceUnderground Storage Tanks · 2.6 mi
- The Garage Auto CareUnderground Storage Tanks · 2.6 mi
- Minnesota Dept Of TransportationUnderground Storage Tanks · 2.6 mi
- 422744Nitrate · 6.5 mi
- AGGREGATE INDUSTRIES INC - MAHNOMENBrownfields · 7.0 mi
- TRUE NORTH EQUIPMENT - MAHNOMBrownfields · 7.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Mahnomen County's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Mahnomen County.
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 across Mahnomen County. 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 1,086 plant recommendations.
25+ data sources read at your address, not the Mahnomen County average
Your land is one point inside Mahnomen County
Everything above resolves to Mahnomen County as a whole — one PHZM band and one county frost record, read across 357K acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at county scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better county average.
Your Lot vs the Mahnomen County Average
Mahnomen County Average
- ●USDA Zones 4a, averaged across Mahnomen County
- ●One soil character for all of Mahnomen County
- ●Frost dates read at Mahnomen County's scale: Apr 30 to Oct 9
YOUR Parcel
- ✓Your exact zone, not Mahnomen County's 4a
- ✓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 lot that Mahnomen County averages can't show:
We read public map data around Mahnomen County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Mahnomen County average
How we know this about Mahnomen County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Mahnomen County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Mahnomen County
When does frost risk typically end in Mahnomen County?
The last hard freeze (28°F) in Mahnomen County typically lands around Apr 30, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about May 21.
How long is the growing season in Mahnomen County?
Measured between 28°F hard freezes, Mahnomen County sees about 162 frost-free days — roughly Apr 30 through Oct 9, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 21 to Sep 25, about 127 days.
Is the soil safe to grow vegetables in Mahnomen County?
The federal record around Mahnomen County shows 71 documented sites, mostly Underground Storage Tanks entries (29), the nearest Underground Storage Tanks record about 1.0 miles out — 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.
Everything above is measured at Mahnomen County's scale — its 4a band and its 162-day season. Your yard writes its own version of Mahnomen County's numbers: 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.
What this page reads at Mahnomen County’s own scale
8 of the readings below were taken at Mahnomen County's own scale — its own ~162-day span between 28°F freezes, the 3 most extensive soil series mapped here and 71 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Mahnomen County's own USDA hardiness band, zones 4aUSDA PHZM 2023
- Mahnomen County's own 28°F hard-freeze dates and its ~162-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Mahnomen CountyUSDA NRCS SSURGO
- 71 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 1.0 miles outFederal environmental registers
- Mahnomen County's boundary and the 357,034 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4a and a ~162-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Mahnomen County spans, Lake Agassiz Plain the largestUS EPA Level III Ecoregions
- Which agricultural compounds go onto Mahnomen County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Minnesota grower plans around — written at state scale, so they stay on the state guidefrom Minnesota
What this page can’t tell you
- How the season shifts across Mahnomen County — the ~162 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Mahnomen County's 357,034 acreswhy one lot differs from the next →
- Which of those 71 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Mahnomen Countyread your own land →