Lewis and Clark County, in Montana, sits in USDA hardiness zone 4b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Crops well matched to these conditions include cabbage, cranberry, cilantro, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Lewis and Clark County holds more than one microclimate.
Soils and elevations shift across Lewis and Clark 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 Lewis and Clark County — soil, climate, flood, and parcel records. How we handle your address.
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Lewis and Clark County — the short answer
Lewis and Clark County, Montana: USDA zone 4b, about 124 days between hard freezes, across 2.2M acres.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 15
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 16
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~124
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 2.2M 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 4b is Lewis and Clark County's average, not your lot's — a low corner or a tree line moves it. Against Lewis and Clark County's 124-day season, see what your own ground reads.
One county, several growing seasons
Lewis and Clark County's hard-freeze record runs about 124 days between freezes — but that is the county-wide average, and several towns inside it carry a markedly different season in their own 30-year record: Augusta at about 159 days, Gilman at 159 and Helena Valley Northwest at 159 (against the county's ~124).
Those are measured records, not estimates. If you garden in one of these pockets, plant against your own town's season rather than the county's ~124-day average.
NOAA Regional Climate Centers ACIS (1991–2020), 30-year daily minimum record. Only held-out towns carrying their own record are named — a town with no record of its own is absent rather than estimated, and a county with nothing qualifying shows no spread at all.
Heat in Lewis and Clark County
Across a year, Lewis and Clark County accumulates about 738 growing degree days above 50°F, about 932 fewer than the middle Montana county — ahead of 4 of Montana’s 56 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 Lewis and Clark County
Across Lewis and Clark County, the ground is predominantly Mollisols, where Reeder, Tolex, and Mocmont are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.1–7.2, neutral. Rainfall drains through hydrologic group D soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
0%
Hydric soils
1%
Soil still varies lot by lot — soil types explained.
How the ground varies across Lewis and Clark County
The USDA soil survey maps 74% of Lewis and Clark County as well drained — but another 4% drains differently: 2% poorly drained, 1% somewhat poorly drained.
Reeder is the most extensive named soil at 4% of mapped acres, then Tolex (4%) and Mocmont (4%).
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 Lewis and Clark County
Each reading below is measured for Lewis and Clark 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 Lewis and Clark County are well drained, in hydrologic group 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 Lewis and Clark County runs about pH 6.1–7.2, 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
Season length
MeasuredLewis and Clark County runs about 124 days between hard freezes — a short growing season.
Long-maturing crops like melons, sweet potatoes, and winter squash can run out of runway before the first hard freeze, ripening late or not at all.
Lead with fast-maturing varieties, and stretch the season on both ends with cold frames, low tunnels, or a greenhouse.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredLewis and Clark County sits in USDA hardiness zone 4b.
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 Lewis and Clark County is in
Lewis and Clark County spans 3 EPA Level III ecoregions — Middle Rockies (52%), Canadian Rockies (22%) and Northwestern Glaciated Plains (22%). 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 Lewis and Clark County
We scored all 1,086 plants against Lewis and Clark County's own USDA zone 4b and its own 124-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 Montana profile.
Is it too late to plant in Lewis and Clark County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 17; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 16 — long-season crops need about 90 days of runway, quick greens only 30. In a season this compact, fast finishers and cold-hardy greens do the late work, and garlic tucked in before the freeze repays you next summer.
What gets applied to farmland in Lewis and Clark County
USGS estimates 31,837 lb of Glyphosate on Lewis and Clark County farmland in 2019, its largest by weight, ahead of 2,4-d (10,714 lb) and Bromoxynil (3,508 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 Lewis and Clark County — and how to grow with it.
We checked the federal record across Lewis and Clark County — 1,459 documented sites across 8 of the 9 source types we track.
The most significant on record: 17 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Lewis and Clark County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Lewis and Clark County
Closest first, across Lewis and Clark County. Listing isn't leaking, and distance isn't exposure.
- AT & T COMMUNICATIONS SIMMS RADIOUnderground Storage Tanks · 0.6 mi
- Copper Bowl MineMining · 1.5 mi
- Roger's Pass' ClaimMining · 4.3 mi
- Gossan & Junior ClaimsMining · 4.4 mi
- Carbonate HillMining · 4.5 mi
- R. T. C. LodeMining · 4.7 mi
- Ward ThompsonMining · 4.7 mi
- MillironMining · 4.8 mi
- Red Rock ClaimsMining · 5.0 mi
- MidnightMining · 5.1 mi
- Rex BeachMining · 5.2 mi
- Adele MineMining · 5.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Lewis and Clark 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 Lewis and Clark County.
Sources Checked
across Lewis and Clark County
Severity Distribution
across Lewis and Clark County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Lewis and Clark County, two things run higher than the national average across Lewis and Clark County — Mining (348 sites) and Nitrate (688 sites). 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.
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).
Check your specific parcel in Lewis and Clark 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 Lewis and Clark County average
Your land is one point inside Lewis and Clark County
Everything above resolves to Lewis and Clark County as a whole — one PHZM band and one county frost record, read across 2.2M 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 Lewis and Clark County Average
Lewis and Clark County Average
- ●USDA Zones 4b, averaged across Lewis and Clark County
- ●One soil character for all of Lewis and Clark County
- ●Frost dates read at Lewis and Clark County's scale: May 15 to Sep 16
YOUR Parcel
- ✓Your exact zone, not Lewis and Clark County's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Lewis and Clark County
Pull a site-specific report for your exact address in Lewis and Clark County, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Lewis and Clark County averages can't show:
We read public map data around Lewis and Clark County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Lewis and Clark County average
How we know this about Lewis and Clark 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 Lewis and Clark County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Lewis and Clark County
When does frost risk typically end in Lewis and Clark County?
The last hard freeze (28°F) in Lewis and Clark County typically lands around May 15, 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 Jun 5.
How long is the growing season in Lewis and Clark County?
Measured between 28°F hard freezes, Lewis and Clark County sees about 124 frost-free days — roughly May 15 through Sep 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 5 to Sep 2, about 89 days.
Is the soil safe to grow vegetables in Lewis and Clark County?
The federal record around Lewis and Clark County runs heavier than most — 1,459 documented sites, mostly Nitrate entries (688), the nearest Underground Storage Tanks record about 0.6 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 gardeners stretch the season in Lewis and Clark County?
With about 124 frost-free days between hard freezes, Lewis and Clark County rewards the classic extension moves: floating row cover buys roughly two to four extra weeks at each shoulder — on this season that is a working window nearer 152 to 180 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 15 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Lewis and Clark County's scale — its 4b band and its 124-day season. Your yard writes its own version of Lewis and Clark 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 Montana's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Lewis and Clark County’s own scale
8 of the readings below were taken at Lewis and Clark County's own scale — its own ~124-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,459 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Lewis and Clark County's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Lewis and Clark County's own 28°F hard-freeze dates and its ~124-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Lewis and Clark CountyUSDA NRCS SSURGO
- 1,459 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.6 miles outFederal environmental registers
- Lewis and Clark County's boundary and the 2,213,361 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~124-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Lewis and Clark County spans, Middle Rockies the largestUS EPA Level III Ecoregions
- Which agricultural compounds go onto Lewis and Clark County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Montana grower plans around — written at state scale, so they stay on the state guidefrom Montana
What this page can’t tell you
- How the season shifts across Lewis and Clark County — the ~124 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 Lewis and Clark County's 2,213,361 acreswhy one lot differs from the next →
- Which of those 1,459 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 Lewis and Clark Countyread your own land →