Thief River Falls, Minnesota, sits in USDA hardiness zone 4a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
A short list that earns its place here — cabbage, cranberry, turkish rocket, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Even in Thief River Falls, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Thief River Falls lot. 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 Thief River Falls — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Thief River Falls — the short answer
Thief River Falls, Minnesota: USDA zone 4a, about 160 days between hard freezes, across 4K acres of city.
- USDA zone
- 4a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 30
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~160
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 4K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 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 Thief River Falls's average, not your lot's — a low corner or a tree line moves it. Against Thief River Falls's 160-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Thief River Falls
Each reading below is measured for Thief River Falls itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredThief River Falls runs about 160 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
Winter hardiness
MeasuredThief River Falls sits in USDA hardiness zone 4a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Thief River Falls is in
Thief River Falls sits in the Lake Agassiz Plain — EPA Level III, inside the wider Great Plains. That is read at Thief River Falls's own centroid rather than borrowed from Pennington County.
What Grows in Thief River Falls
Every plant below cleared Thief River Falls's own zone 4a and its 160-day season. Each card opens that plant's Minnesota profile. How we score.
Is it too late to plant in Thief River Falls?
Usually not — gardeners here simply switch what goes in the ground as the season moves. 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 7 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
What's on the federal record near Thief River Falls
Closest first, within ~10 miles of Thief River Falls. Listing isn't leaking, and distance isn't exposure.
- UNRUH JERRYBrownfields · 350 ft
- NORTHERN PRIDE, INC.Brownfields · 450 ft
- THIEF RIVER FALLS WATER TREATMENT PLANTBrownfields · 1300 ft
- ALS REPAIR INCBrownfields · 1600 ft
- THIEF RIVER FALLS TACCBrownfields · 1600 ft
- ISD 564Brownfields · 1600 ft
- THIEF RIVER FALLS CITY OF - POWER PLANTBrownfields · 1700 ft
- Northdale Oil Inc dba Pennington SquareUnderground Storage Tanks · 1900 ft
- PENNINGTON FAST LUBEBrownfields · 2000 ft
- ISD 564 School District Service CenterUnderground Storage Tanks · 2000 ft
- VALLEY HOMEBrownfields · 2100 ft
- SANFORD THIEF RIVER FALLS MEDICAL CENTER - TRFBrownfields · 2200 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Thief River Falls'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 Thief River Falls.
Total Sites
150
within ~10 miles of Thief River Falls
Risk Level
Moderate
Highest-severity
6 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Thief River Falls
Severity Distribution
within ~10 miles of Thief River Falls
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Thief River Falls, Brownfields runs higher than the national average — 73 sites within ~10 miles of Thief River Falls. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Brownfields: Brownfield sites are former commercial or industrial properties where legacy soil contamination (heavy metals, PAHs, petroleum compounds) may persist.
Check EPA brownfield remediation status — many sites have completed cleanup with institutional controls.
Check your specific parcel in Thief River Falls
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 Thief River Falls average
Your land is one point inside Thief River Falls
Everything above resolves to Thief River Falls as a whole — one PHZM band and one 28°F frost record, read across 4K 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 city 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 local average.
Your Lot vs the Thief River Falls Average
Thief River Falls Average
- ●USDA Zones 4a, averaged across Thief River Falls
- ●One soil character for all of Thief River Falls
- ●Frost dates read at Thief River Falls's scale: Apr 30 to Oct 7
YOUR Parcel
- ✓Your exact zone, not Thief River Falls's 4a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Thief River Falls
Pull a site-specific report for your exact address in Thief River Falls, Minnesota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Thief River Falls averages can't show:
We read public map data around Thief River Falls — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Thief River Falls average
How we know this about Thief River Falls
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Thief River Falls’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Thief River Falls
When does frost risk typically end in Thief River Falls?
The last hard freeze (28°F) in Thief River Falls 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.
When is the first frost in Thief River Falls?
The first hard freeze (28°F) in Thief River Falls typically arrives around Oct 7, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 23, so the watching starts about Sep 7 — about 160 days after the spring freeze cleared.
How long is the growing season in Thief River Falls?
Measured between 28°F hard freezes, Thief River Falls sees about 160 frost-free days — roughly Apr 30 through Oct 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 21 to Sep 23, about 125 days.
Is the soil safe to grow vegetables in Thief River Falls?
The federal record around Thief River Falls shows 150 documented sites, mostly Brownfields entries (73), the nearest Brownfields record under a tenth of a mile 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.
How do I protect my plants from frost in Thief River Falls?
From about Sep 7 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 7 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 7. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Thief River Falls's scale — its 4a band and its 160-day season. Your yard writes its own version of Thief River Falls's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Thief River Falls’s own scale
6 of the readings below were taken at Thief River Falls's own scale — its own ~160-day season between 28°F freezes, the 3,842 acres it covers and 150 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Thief River Falls's own USDA hardiness band, zones 4aUSDA PHZM 2023
- Thief River Falls's own 28°F hard-freeze dates, about Apr 30 and Oct 7 and the ~160-day span between themNOAA 1991–2020 Climate Normals
- 150 documented contamination sites on the federal record near Thief River Falls, the closest Brownfields record under a tenth of a mile out from the town centreFederal environmental registers
- Thief River Falls's boundary and the 3,842 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4a and a ~160-day seasonGrowable Ground crop-matching engine
- The ecoregion at Thief River Falls's own centroid, the Lake Agassiz PlainUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Thief River Falls's 3,842 acres read through its county's SSURGO summaryfrom Pennington County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Pennington County
- The growing challenges every Minnesota grower plans around — written at state scale, so they stay on the state guidefrom Minnesota
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Pennington County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Thief River Falls's 3,842 acreswhy one lot differs from the next →
- Which side of Thief River Falls you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 3,842 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields record under a tenth of a mile out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Thief River Falls-wide figureread your own land →
More in Minnesota
Growing region
Nearby growing guides