The Flathead Valley spans USDA hardiness zones 5b-6a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
A mountain-ringed northwest Montana valley whose big lake buffers the cold — sweet cherries on the lakeshore benches, with mint, grain, and hay on the valley floor. These conditions suit potato, lentil, cherry, and rhubarb — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
The Flathead Valley spans Montana.
Your yard isn't all of the Flathead Valley.
The Flathead Valley spans USDA zones 5b-6a, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 Flathead Valley — soil, climate, flood, and parcel records. How we handle your address.
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The Flathead Valley — the short answer
The Flathead Valley: USDA zones 5b-6a, 132–167 frost-free days depending where in it you stand, in Montana.
- USDA zones
- 5b-6a
- USDA PHZM 2023, aggregated over the footprint
- Shortest season here
- 132 days
- NOAA Regional Climate Centers ACIS, 1991-2020 — Flathead County
- Counties
- 2
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. The season figure is this region's own record, measured across its 2 member counties, not a state or national average.
Hardiness Zone Range
The Flathead Valley is not one growing season
One answer for the Flathead Valley averages 2 counties whose growing seasons are 35 days apart — from 132 frost-free days in Flathead County to 167 in Lake County. That is the same region, measured the same way, in the same years. Which end of it your land sits nearer decides what finishes before the first hard freeze.
The middle half of 2 counties runs 141–158 days, with a median of 150 days — a 35-day span end to end.
Measured across 2 member counties, each carrying its own 28°F normal. NOAA Regional Climate Centers ACIS, 1991-2020. A member with no own record is absent from the range rather than counted as zero — nothing here is interpolated to the region. Your own site sits somewhere inside this range; a parcel report resolves where.
Where the line runs inside the Flathead Valley
The middle half of the Flathead Valley runs 141–158 frost-free days, and 2 of its 2 counties sit outside that — 1 on the short side, 1 on the long. A regional planting date describes the middle well and the ends poorly, which is worth knowing before you follow one.
Under 141 frost-free days
1 county
- Flathead County · 132 days
The end of the region that sets the planting calendar — start seed indoors here and the season stretches to meet the crop.
Over 158 frost-free days
1 county
- Lake County · 167 days
Long enough for a second succession of a quick crop after the first comes out.
Each county is placed by its OWN 28°F frost-free normal (NOAA Regional Climate Centers ACIS, 1991-2020), the same figure its own guide page publishes. Elevation, slope and cold-air drainage move a site within its county as well — which is the part only your address resolves.
What Grows in the Flathead Valley
All 2 of the plants below that publish a season requirement clear even Flathead County’s 132 frost-free days — so on season alone, this grid works at both ends of the region. The 35-day spread still decides how far past this list you can push, and how early you can start.
Plants matched to the Flathead Valley's USDA zones 5b-6a, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the Flathead Valley
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the Flathead Valley’s USDA zones 5b-6a — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the Flathead Valley
The USDA soil survey maps this ground county by county. These are those records weighted by land area across two member counties — this region’s own profile, not a state figure.
The ground is predominantly Inceptisols, at 53% of mapped acres, followed by Alfisols (21%), Mollisols (16%) and Andisols (6%). Seven soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Bigarm, Winkler, and Mitten.
45% of those acres are well drained, and another 13% somewhat excessively drained, 2% excessively drained. Topsoil pH runs 5.6–7.0 between the lowest and the highest county on record. 1% of the footprint is classed prime farmland.
Soil order
Inceptisols
Drainage
Well drained
Topsoil pH
5.6–7.0
Hydric soils
2%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. Lake County holds the most wetland ground here, at 2% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the Flathead Valley
The soil survey reads this ground county by county, and the readings above are those records summed across the Flathead Valley. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records45% of the mapped acres across the Flathead Valley are well drained — ground that drains quickly. That is area-weighted across all two of its mapped counties.
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
From county recordsTopsoil across the Flathead Valley runs pH 5.6–7.0 — near neutral in all two of them.
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
Safe to Grow Here?
What the federal record shows across the Flathead Valley — and how to grow with it.
Across the Flathead Valley's 2 counties the federal record holds 989 documented sites, mostly Underground Storage Tanks (432), Nitrate (322) and Brownfields (131). The heaviest single county is Flathead County, with 652.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the Flathead Valley to see which records sit where you actually grow.
Sources Checked
Summed across the 2 counties in the Flathead Valley
A note from Gnorman
What an experienced grower watches for around here
In and around the Flathead Valley, two things run higher than the national average across the 2 counties in the Flathead Valley — Mining (78 sites) and Nitrate (322 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the Flathead Valley
Everything above resolves to the Flathead Valley as a whole — a footprint whose own counties record seasons 35 days apart, and hardiness across zones 5b-6a. Your parcel sits at one point in that range, not in the middle of it. 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 region 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 regional average.
Your Lot vs the Flathead Valley Average
Flathead Valley Average
- ●USDA Zones 5b-6a, averaged across Flathead Valley
- ●One soil character for all of Flathead Valley
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not Flathead Valley's 5b-6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the Flathead Valley
Pull a site-specific report for your exact address in the Flathead Valley — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that Flathead Valley averages can't show:
We read public map data around The Flathead Valley — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Flathead Valley average
How we know this about the Flathead Valley
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the Flathead Valley
What hardiness zone is the Flathead Valley?
The Flathead Valley spans USDA hardiness zones 5b-6a, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the Flathead Valley?
Measured between 28°F hard freezes, the Flathead Valley's counties mostly run 141 to 158 frost-free days, median 150 (NOAA Regional Climate Centers ACIS, 1991–2020, over 2 member counties). That 17-day spread is the honest read — no single season describes 2 counties, and each county guide below carries its own.
When does frost risk end in the Flathead Valley?
Across the Flathead Valley, the middle half of member counties see their last 28°F hard freeze between May 3 and May 14 (median May 9), and their first fall freeze between Oct 2 and Oct 9. Those are hard freezes, not the last light frost: tender transplants wait for about May 30, and elevation decides which end of a 11-day spread you garden in.
What grows well in the Flathead Valley?
The Flathead Valley's conditions suit plants such as Potato, Lentil, Cherry, Rhubarb, Ponderosa Pine. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the Flathead Valley defined?
The Flathead Valley is defined here as a curated cluster of 2 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the Flathead Valley cover?
The Flathead Valley spans Montana. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
The Hi-Line, The Yellowstone Valley, The Rocky Mountain Front / Great Falls Chinook Belt, Bitterroot Valley, Gallatin Valley, and Paradise Valley share at least one state with the Flathead Valley. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the Flathead Valley’s own scale
6 of the readings below were taken at the Flathead Valley's own scale — the zone 5b-6a band across its footprint, a median 150-day season across its 2 counties and 989 documented federal contamination records across its 2 counties, 652 of them in Flathead County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 5b-6a aggregated across all 2 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 2 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 2 counties run 141 to 158 frost-free days, median 150NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 989 documented federal contamination records across its 2 counties, 652 of them in Flathead County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 53% Inceptisols, topsoil pH 5.6–7.0, area-weighted across its 2 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 5b-6afrom Montana
What this page can’t tell you
- Which end of the 17-day range your ground sits at — 141 days at one extreme, 158 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the Flathead Valley
State growing guides
Counties in this region
Other growing regions across Montana
Montana's coldest, driest strip — the northern-border county tier along US Highway 2 and the BNSF (old Great Northern) line — and the only Growable Ground region reaching USDA zone 3b: the Daniels–Sheridan–Roosevelt corner sits at 3b with just 142–146 frost-free days, a full zone colder than the 5a–6a mountain valleys captured elsewhere in the state. The western and central counties run 4a with 140–159 frost-free days. This is semi-arid dryland-wheat country with extreme winter minima and wide day-to-night diurnal swings; chinook winds moderate only the Glacier–Toole western end, leaving the shortest, most cold-hardy growing palette anywhere in Montana. None of that growing reality is visible on the sprawling statewide page.
Montana's longest growing season sits at its coldest-looking zones. The Yellowstone River bottomland from Billings down to Sidney runs 153-166 frost-free days (county_data.json) across USDA zones 4a-4b — a genuinely longer window than the state's 5a-6a mountain valleys, which sit in warmer zones but freeze sooner (Gallatin 114, Madison 117, Ravalli 146 frost-free days). That long, irrigated plains river-bottom season is what carries the corridor's sugar beets, corn, and full-season vegetables, and it is a distinctly different growing experience from Montana's SW/NW mountain valleys or the Hi-Line that a statewide average flattens away.
Where the northern plains slam into the Rocky Mountain Front, chinook winds rewrite the rules of a zone-4 winter. Great Falls earns its "banana belt of the north" name because these warm, dry downslope gales can lift a February morning tens of degrees in an hour — sparing tender crowns the deep cold the Hi-Line just east endures. The same wind is the catch: it desiccates exposed evergreens and perennials and whipsaws plantings through thaw-freeze cycles that split bark and heave roots. Here the decisive question isn't your zone (4a–4b, roughly 140–159 frost-free days) but your parcel's exposure to the Front — which slopes, shelterbelts, and wind-lees the chinook finds, and which it spares.
The Bitterroot Valley runs roughly 95 miles along the Bitterroot River between the Bitterroot Range and the Sapphire Mountains, spanning Ravalli and Missoula counties (USGS) across USDA hardiness zones 5b-6a, where a short 137-to-146-day frost-free season closes early: both counties typically see first frost by late September.
Southwest Montana's Gallatin Valley, the Bozeman-area basin, sits in USDA zone 5a with a short ~114-day frost-free growing season — the last spring frost typically holds until early June and the first fall frost returns by late September.
Paradise Valley traces the Yellowstone River through Montana's Park County, where USDA zone 5a and a roughly 125-day frost-free season — last frost in late May, first frost in late September — shape a short, high-elevation growing window.