Thompson Falls, Montana, sits in USDA hardiness zone 6a — 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 cabbage, blackberry, california poppy, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Even in Thompson 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 Thompson 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 Thompson Falls — soil, climate, flood, and parcel records. How we handle your address.
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Thompson Falls — the short answer
Thompson Falls, Montana: USDA zone 6a, about 160 days between hard freezes, across 1K acres of city.
- USDA zone
- 6a
- 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
- 1K 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 6a is Thompson Falls's average, not your lot's — a low corner or a tree line moves it. Against Thompson 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 Thompson Falls
Each reading below is measured for Thompson Falls itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredThompson 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
MeasuredThompson Falls sits in USDA hardiness zone 6a.
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 Thompson Falls is in
Thompson Falls sits in the Northern Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Thompson Falls's own centroid rather than borrowed from Sanders County.
What Grows in Thompson Falls
Every plant below cleared Thompson Falls's own zone 6a and its 160-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Thompson Falls?
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 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 Thompson Falls
Closest first, within ~10 miles of Thompson Falls. Listing isn't leaking, and distance isn't exposure.
- ABANDONED GAS STATION BIRDLAND BAYUnderground Storage Tanks · 1900 ft
- THOMPSON FALLS AIRPORTUnderground Storage Tanks · 1900 ft
- THOMPSON FALLS MICROWAVEUnderground Storage Tanks · 1900 ft
- NEALS EXXONUnderground Storage Tanks · 2000 ft
- NEW ASIA RESTAURANTUnderground Storage Tanks · 2100 ft
- RONS SERVICEUnderground Storage Tanks · 2100 ft
- MOUNTAIN WEST CO OP CENEXUnderground Storage Tanks · 2300 ft
- ELEMENTARY SCHOOLUnderground Storage Tanks · 2400 ft
- CITY HALLUnderground Storage Tanks · 2400 ft
- MOUNTAIN MUSICUnderground Storage Tanks · 2500 ft
- THOMPSON FALLS FEED AND FUEL LLCUnderground Storage Tanks · 2600 ft
- TOWN PUMP INC THOMPSON FALLSUnderground Storage Tanks · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Thompson 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 Thompson Falls.
Total Sites
53
within ~10 miles of Thompson Falls
Risk Level
High
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
within ~10 miles of Thompson Falls
Severity Distribution
within ~10 miles of Thompson Falls
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Thompson Falls, Mining runs higher than the national average — 23 sites within ~10 miles of Thompson Falls. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Thompson 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 Thompson Falls average
Your land is one point inside Thompson Falls
Everything above resolves to Thompson Falls as a whole — one PHZM band and one 28°F frost record, read across 1K 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 Thompson Falls Average
Thompson Falls Average
- ●USDA Zones 6a, averaged across Thompson Falls
- ●One soil character for all of Thompson Falls
- ●Frost dates read at Thompson Falls's scale: Apr 30 to Oct 7
YOUR Parcel
- ✓Your exact zone, not Thompson Falls's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Thompson Falls
Pull a site-specific report for your exact address in Thompson Falls, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Thompson Falls averages can't show:
We read public map data around Thompson Falls — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Thompson Falls average
How we know this about Thompson 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 Thompson 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 Thompson Falls
When does frost risk typically end in Thompson Falls?
The last hard freeze (28°F) in Thompson 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 Thompson Falls?
The first hard freeze (28°F) in Thompson 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 Thompson Falls?
Measured between 28°F hard freezes, Thompson 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 Thompson Falls?
The federal record around Thompson Falls runs heavier than most — 53 documented sites, mostly Underground Storage Tanks entries (24), the nearest Underground Storage Tanks record about 0.4 miles out — 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.
How do I protect my plants from frost in Thompson 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 Thompson Falls's scale — its 6a band and its 160-day season. Your yard writes its own version of Thompson 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 Thompson Falls’s own scale
6 of the readings below were taken at Thompson Falls's own scale — its own ~160-day season between 28°F freezes, the 1,027 acres it covers and 53 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Thompson Falls's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Thompson 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
- 53 documented contamination sites on the federal record near Thompson Falls, the closest Underground Storage Tanks record about 0.4 miles out from the town centreFederal environmental registers
- Thompson Falls's boundary and the 1,027 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~160-day seasonGrowable Ground crop-matching engine
- The ecoregion at Thompson Falls's own centroid, the Northern RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Thompson Falls's 1,027 acres read through its county's SSURGO summaryfrom Sanders County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Sanders County
- The growing challenges every Montana grower plans around — written at state scale, so they stay on the state guidefrom Montana
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Sanders County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Thompson Falls's 1,027 acreswhy one lot differs from the next →
- Which side of Thompson 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 1,027 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.4 miles 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 Thompson Falls-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaThompson Falls sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides