Forty Mile Colony, 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.
These conditions suit cabbage, cranberry, cilantro, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Even in Forty Mile Colony, 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 Forty Mile Colony 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 Forty Mile Colony — soil, climate, flood, and parcel records. How we handle your address.
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Forty Mile Colony — the short answer
Forty Mile Colony, Montana: USDA zone 4b, about 149 days between hard freezes, across 122 acres of town.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 6
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 2
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~149
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 122 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 4b is Forty Mile Colony's average, not your lot's — a low corner or a tree line moves it. Against Forty Mile Colony's 149-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Forty Mile Colony
Each reading below is measured for Forty Mile Colony itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredForty Mile Colony runs about 149 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
MeasuredForty Mile Colony 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 Forty Mile Colony is in
Forty Mile Colony sits in the Northwestern Great Plains — EPA Level III, inside the wider Great Plains. That is read at Forty Mile Colony's own centroid rather than borrowed from Big Horn County.
What Grows in Forty Mile Colony
Every plant below cleared Forty Mile Colony's own zone 4b and its 149-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Forty Mile Colony?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Apr 8; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 6 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 2 — long-season crops need about 90 days of runway, quick greens only 30. When the window is tight, the fall moves are quick ones — baby greens, radishes, and garlic set for next season.
What's on the federal record near Forty Mile Colony
Closest first, within ~10 miles of Forty Mile Colony. Listing isn't leaking, and distance isn't exposure.
- 06S35E36BCBC02Nitrate · 1.3 mi
- LODGE GRASS DRUMSSuperfund · 1.6 mi
- LODGE GRASS DRUM SITEBrownfields · 1.6 mi
- 06S35E13CDCB01Nitrate · 1.7 mi
- BIG HORN COUNTY ROAD DEPT LODGE GRASSUnderground Storage Tanks · 1.9 mi
- THE STATION LODGE GRASSUnderground Storage Tanks · 2.0 mi
- INDIAN HEALTH SERVICE LODGE GRASSUnderground Storage Tanks · 2.0 mi
- 06S35E13AC 01Nitrate · 2.1 mi
- MONTANA DEPARTMENT OF TRANSPORATION LODGE GRASSBrownfields · 2.3 mi
- LODGE GRASS SCHOOL DIST 27Underground Storage Tanks · 2.3 mi
- 06S35E14DB 01Nitrate · 2.3 mi
- 06S35E13BA 01Nitrate · 2.4 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Forty Mile Colony'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 Forty Mile Colony.
Total Sites
74
within ~10 miles of Forty Mile Colony
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Forty Mile Colony
Severity Distribution
within ~10 miles of Forty Mile Colony
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Forty Mile Colony, Nitrate runs higher than the national average — 60 sites within ~10 miles of Forty Mile Colony. 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 Forty Mile Colony
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 Forty Mile Colony average
Your land is one point inside Forty Mile Colony
Everything above resolves to Forty Mile Colony as a whole — one PHZM band and one 28°F frost record, read across 122 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 town 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 Forty Mile Colony Average
Forty Mile Colony Average
- ●USDA Zones 4b, averaged across Forty Mile Colony
- ●One soil character for all of Forty Mile Colony
- ●Frost dates read at Forty Mile Colony's scale: May 6 to Oct 2
YOUR Parcel
- ✓Your exact zone, not Forty Mile Colony's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Forty Mile Colony
Pull a site-specific report for your exact address in Forty Mile Colony, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Forty Mile Colony averages can't show:
We read public map data around Forty Mile Colony — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Forty Mile Colony average
How we know this about Forty Mile Colony
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Forty Mile Colony’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 town grain anywhere on this page — there is no town-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 Forty Mile Colony
When does frost risk typically end in Forty Mile Colony?
The last hard freeze (28°F) in Forty Mile Colony typically lands around May 6, 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 27.
When is the first frost in Forty Mile Colony?
The first hard freeze (28°F) in Forty Mile Colony typically arrives around Oct 2, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 18, so the watching starts about Sep 2 — about 149 days after the spring freeze cleared.
How long is the growing season in Forty Mile Colony?
Measured between 28°F hard freezes, Forty Mile Colony sees about 149 frost-free days — roughly May 6 through Oct 2, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 27 to Sep 18, about 114 days.
Is the soil safe to grow vegetables in Forty Mile Colony?
The federal record around Forty Mile Colony is a meaningful one — 74 documented sites, mostly Nitrate entries (60), the nearest Nitrate record about 1.3 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do gardeners stretch the season in Forty Mile Colony?
With about 149 frost-free days between hard freezes, Forty Mile Colony 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 177 to 205 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 6 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Forty Mile Colony's scale — its 4b band and its 149-day season. Your yard writes its own version of Forty Mile Colony'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 Forty Mile Colony’s own scale
6 of the readings below were taken at Forty Mile Colony's own scale — its own ~149-day season between 28°F freezes, the 122 acres it covers and 74 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Forty Mile Colony's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Forty Mile Colony's own 28°F hard-freeze dates, about May 6 and Oct 2 and the ~149-day span between themNOAA 1991–2020 Climate Normals
- 74 documented contamination sites on the federal record near Forty Mile Colony, the closest Nitrate record about 1.3 miles out from the town centreFederal environmental registers
- Forty Mile Colony's boundary and the 122 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~149-day seasonGrowable Ground crop-matching engine
- The ecoregion at Forty Mile Colony's own centroid, the Northwestern Great PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Forty Mile Colony's 122 acres read through its county's SSURGO summaryfrom Big Horn County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Big Horn 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 Big Horn County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Forty Mile Colony's 122 acreswhy one lot differs from the next →
- Which side of Forty Mile Colony you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 122 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 1.3 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 Forty Mile Colony-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaForty Mile Colony sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides