Petroleum 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.
On paper, cherry, potato, lentil, and ponderosa pine all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Petroleum County holds more than one microclimate.
Soils and elevations shift across Petroleum County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,112 plants against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Quick Facts
USDA Zones
4b
Last Hard Freeze (28°F)
Apr 15
County normal — light frosts run a few weeks later
First Hard Freeze (28°F)
Oct 21
County normal — light frosts arrive a few weeks earlier
County Area
1.1M acres
Hardiness Zone Range
Zone maps are averages across Petroleum County. Your yard's slope, trees, and frost pockets shift what actually grows — see your land's exact reading.
Soil in Petroleum County
Across Petroleum County, the ground is predominantly Entisols, where Neldore, Gerdrum, and Cabbart are the most extensive named soil series. The soil is generally well drained with a silty clay surface. Topsoil pH runs about 6.7–7.9, neutral. Rainfall drains through hydrologic group D soils.
Soil order
Entisols
Drainage
Well drained
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
What Grows in Petroleum County
Plants matched to Petroleum County's USDA zones 4b — each links to its full growing profile.
Is it too late to plant in Petroleum County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 21 — long-season crops need about 90 days of runway, quick greens only 30. Late in the year the fall bench takes over — quick greens, radishes, and garlic that repays you next summer.
Growing Challenges in Montana
What an experienced grower plans around here — each one has a move.
Very short growing season (60-100 frost-free days)
At 60-100 frost-free days, a high tunnel or cold frame isn't a luxury — it's the difference-maker Montana growers rely on.
Low rainfall requires irrigation in most areas
Drip irrigation plus mulch stretches scarce water a long way — plan the system before the first seed.
Extreme winter cold (-40F possible)
Choose perennials rated for the cold you actually get — a -40°F winter audits every optimistic zone push.
For cultivar selection, pest pressure, and planting-time guidance specific to Montana, the Montana State University Extension is the authoritative local source.
Safe to Grow Here?
What the federal record shows across Petroleum County — and how to grow with it.
We checked the federal record across Petroleum County — 75 documented sites across 2 of the 9 source types we track.
The most significant on record: 66 nitrate monitoring sites. Agricultural runoff and septic contamination — tracked at public water utilities (service-area exposure), private wells, and groundwater monitoring sites.
The federal record across Petroleum County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Environmental Intelligence
Understanding what's nearby helps you make informed decisions about where and how to grow.
Severity Distribution
across Petroleum County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Petroleum County, Nitrate runs higher than the national average — 66 sites nearby. 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 Petroleum County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,112 plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Your Specific Parcel Matters
Petroleum County Average
- ●USDA Zones 4b
- ●Generic soil type for the area
- ●State-average frost dates
YOUR Parcel
- ✓Your exact hardiness zone
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Petroleum County
Pull a site-specific report for your exact address in Petroleum County, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
Key Growing Facts for Petroleum County, Montana
- USDA Hardiness Zones: 4b (USDA PHZM 2023)
- Last Hard Freeze (28°F): Apr 15 (county normal, NOAA 1991–2020 Climate Normals — light frosts can follow for a few weeks)
- First Hard Freeze (28°F): Oct 21 (county normal, NOAA 1991–2020 Climate Normals — light frosts can arrive a few weeks earlier)
- Days Between Hard Freezes: ~189 (county normal, NOAA 1991–2020 Climate Normals)
- County Land Area: 1.1M acres (US Census TIGER 2025)
Zone data: USDA ARS Plant Hardiness Zone Map 2023. Climate data: NOAA NCEI. County boundaries: US Census TIGER/Line 2025.
Frost dates here are the Petroleum County average. Low spots and tree cover move them by days on any one yard — see your exact frost windows.
Frequently Asked Questions
What hardiness zone is Petroleum County, Montana?
Petroleum County sits in USDA hardiness zone 4b, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.
Is it too late to plant in Petroleum County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 21 — long-season crops need about 90 days of runway, quick greens only 30. Late in the year the fall bench takes over — quick greens, radishes, and garlic that repays you next summer.
When does frost risk typically end in Petroleum County?
The last hard freeze (28°F) in Petroleum County typically lands around Apr 15, per NOAA 1991–2020 climate normals — an earlier marker than the light-frost dates many planting charts quote. That marks the hard freeze, not the last light frost — light frosts can still bite for a few more weeks, so tender transplants usually wait another 2–3 weeks.
How long is the growing season in Petroleum County?
Measured between 28°F hard freezes, Petroleum County sees about 189 frost-free days — roughly Apr 15 through Oct 21, per NOAA 1991–2020 climate normals. Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.
What vegetables grow in Petroleum County?
Petroleum County's zone 4b supports a wide range — strong performers include Cherry, Potato, Lentil, Ponderosa Pine, and Rhubarb. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.
Which hardiness zone is Petroleum County, really?
Officially, Petroleum County sits in USDA zone 4b (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.
Is the soil safe to grow vegetables in Petroleum County?
The federal record around Petroleum County shows 75 documented sites — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Just moved to Petroleum County — what should I know before planting?
Start with three facts. Petroleum County sits in USDA zone 4b, which sets what survives winter; the last 28°F hard freeze typically clears around Apr 15, with about 189 frost-free days to work with (NOAA 1991–2020 climate normals); and 75 documented sites sit on the federal record — a typical footprint for a growing area, worth a look on the contamination map before food beds. From there, matching plants to your actual soil and sun is the fun part.
Everything on this page is a Petroleum County average. Your yard writes its own version — 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.