Boulder, Montana, sits in USDA hardiness zone 4b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Among the crops suited to this profile: cabbage, cranberry, cilantro, and collard greens. The site-level story — soil, sun, drainage — decides the rest.
Even in Boulder, 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 Boulder 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 Boulder — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Boulder — the short answer
Boulder, Montana: USDA zone 4b, about 135 days between hard freezes, across 719 acres of city.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 13
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 25
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~135
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 719 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 Boulder's average, not your lot's — a low corner or a tree line moves it. Against Boulder's 135-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Boulder
Each reading below is measured for Boulder itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredBoulder runs about 135 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
MeasuredBoulder 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 Boulder is in
Boulder sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Boulder's own centroid rather than borrowed from Jefferson County.
What Grows in Boulder
Every plant below cleared Boulder's own zone 4b and its 135-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Boulder?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Apr 15; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 25 — 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 Boulder
Closest first, within ~10 miles of Boulder. Listing isn't leaking, and distance isn't exposure.
- JEFFERSON COUNTY SHOP BOULDERUnderground Storage Tanks · 200 ft
- HARLOWS SCHOOL BUS SERVICE INC BOULDERUnderground Storage Tanks · 250 ft
- FRANCHIS CORNERUnderground Storage Tanks · 250 ft
- JEFFERSON COUNTY COURTHOUSE 201 W 3RD STUnderground Storage Tanks · 450 ft
- JEFFERSON COUNTY COURTHOUSEUnderground Storage Tanks · 500 ft
- MONTANA DEVELOPMENT CENTERUnderground Storage Tanks · 600 ft
- JEFFERSON HIGH SCHOOLBrownfields · 600 ft
- MONTANA DEVELOPMENTAL CENTER BOULDERBrownfields · 1000 ft
- 06N04W32AABD01Nitrate · 1200 ft
- 06N04W33BBCD01Nitrate · 1200 ft
- FORMER SERVICE STATION BOULDERUnderground Storage Tanks · 1300 ft
- MDOT BOULDERUnderground Storage Tanks · 1300 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Boulder'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 Boulder.
Total Sites
377
within ~10 miles of Boulder
Risk Level
High
Highest-severity
8 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Boulder
Severity Distribution
within ~10 miles of Boulder
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Boulder, two things run higher than the national average within ~10 miles of Boulder — Mining (285 sites) and Superfund (8 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around 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.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in Boulder
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 Boulder average
Your land is one point inside Boulder
Everything above resolves to Boulder as a whole — one PHZM band and one 28°F frost record, read across 719 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 Boulder Average
Boulder Average
- ●USDA Zones 4b, averaged across Boulder
- ●One soil character for all of Boulder
- ●Frost dates read at Boulder's scale: May 13 to Sep 25
YOUR Parcel
- ✓Your exact zone, not Boulder's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Boulder
Pull a site-specific report for your exact address in Boulder, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Boulder averages can't show:
We read public map data around Boulder — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Boulder average
How we know this about Boulder
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 Boulder’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 Boulder
When does frost risk typically end in Boulder?
The last hard freeze (28°F) in Boulder typically lands around May 13, 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 3.
When is the first frost in Boulder?
The first hard freeze (28°F) in Boulder typically arrives around Sep 25, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 11, so the watching starts about Aug 26 — about 135 days after the spring freeze cleared.
How long is the growing season in Boulder?
Measured between 28°F hard freezes, Boulder sees about 135 frost-free days — roughly May 13 through Sep 25, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 3 to Sep 11, about 100 days.
Is the soil safe to grow vegetables in Boulder?
The federal record around Boulder runs heavier than most — 377 documented sites, mostly Mining entries (285), the nearest Underground Storage Tanks record under a tenth of a mile 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 Boulder?
With about 135 frost-free days between hard freezes, Boulder 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 163 to 191 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 13 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Boulder's scale — its 4b band and its 135-day season. Your yard writes its own version of Boulder'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 Boulder’s own scale
6 of the readings below were taken at Boulder's own scale — its own ~135-day season between 28°F freezes, the 719 acres it covers and 377 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Boulder's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Boulder's own 28°F hard-freeze dates, about May 13 and Sep 25 and the ~135-day span between themNOAA 1991–2020 Climate Normals
- 377 documented contamination sites on the federal record near Boulder, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Boulder's boundary and the 719 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~135-day seasonGrowable Ground crop-matching engine
- The ecoregion at Boulder's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Boulder's 719 acres read through its county's SSURGO summaryfrom Jefferson County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Jefferson 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 Jefferson County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Boulder's 719 acreswhy one lot differs from the next →
- Which side of Boulder you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 719 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks 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 Boulder-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaBoulder sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides