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, cabbage, cranberry, turkish rocket, and collard greens 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 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Petroleum County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Petroleum County — the short answer
Petroleum County, Montana: USDA zone 4b, about 170 days between hard freezes, across 1.1M acres.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 25
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 12
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~170
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.1M 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 Petroleum County's average, not your lot's — a low corner or a tree line moves it. Against Petroleum County's 170-day season, see what your own ground reads.
Heat in Petroleum County
Across a year, Petroleum County accumulates about 2,083 growing degree days above 50°F, about 413 more than the middle Montana county — ahead of 48 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 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.
How the ground varies across Petroleum County
The USDA soil survey maps 97% of Petroleum County as well drained — but another 1% drains differently: 1% moderately well drained.
Neldore is the most extensive named soil at 17% of mapped acres, then Gerdrum (8%) and Cabbart (6%).
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 Petroleum County
Each reading below is measured for Petroleum 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 Petroleum 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 Petroleum County runs about pH 6.7–7.9, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredPetroleum County runs about 170 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredPetroleum 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 Petroleum County is in
Petroleum County sits in the Northwestern Great Plains — EPA Level III, inside the wider Great Plains. One consistent ecological setting across the whole county.
What Grows in Petroleum County
We scored all 1,086 plants against Petroleum County's own USDA zone 4b and its own 170-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 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 28; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 25 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 12 — 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.
What gets applied to farmland in Petroleum County
USGS estimates 35,844 lb of Glyphosate on Petroleum County farmland in 2019, its largest by weight, ahead of 2,4-d (16,241 lb) and Bromoxynil (3,018 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 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.
What's on the federal record near Petroleum County
Closest first, across Petroleum County. Listing isn't leaking, and distance isn't exposure.
- 16N28E22CBD 01Nitrate · 3.3 mi
- 17N27E34AAD 01Nitrate · 5.2 mi
- 15N21E07AAAB01Nitrate · 7.2 mi
- 17N27E30CAC 01Nitrate · 7.3 mi
- 17N28E09DB 01Nitrate · 8.4 mi
- 15N26E13DD 01Nitrate · 8.8 mi
- 15N29E09ADDB01Nitrate · 9.6 mi
- 14N27E05DBB 01Nitrate · 10.7 mi
- HILLTOP SERVICE ARAL INCUnderground Storage Tanks · 10.7 mi
- MDOT 53 3501 WINNETT SITEUnderground Storage Tanks · 11.0 mi
- PETROLEUM COUNTYUnderground Storage Tanks · 11.1 mi
- WINNETT TIREUnderground Storage Tanks · 11.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Petroleum 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 Petroleum County.
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 across Petroleum County. 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 1,086 plant recommendations.
25+ data sources read at your address, not the Petroleum County average
Your land is one point inside Petroleum County
Everything above resolves to Petroleum County as a whole — one PHZM band and one county frost record, read across 1.1M 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 Petroleum County Average
Petroleum County Average
- ●USDA Zones 4b, averaged across Petroleum County
- ●One soil character for all of Petroleum County
- ●Frost dates read at Petroleum County's scale: Apr 25 to Oct 12
YOUR Parcel
- ✓Your exact zone, not Petroleum County's 4b
- ✓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 lot that Petroleum County averages can't show:
We read public map data around Petroleum County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Petroleum County average
How we know this about Petroleum 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 Petroleum County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Petroleum County
When does frost risk typically end in Petroleum County?
The last hard freeze (28°F) in Petroleum County typically lands around Apr 25, 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 16.
How long is the growing season in Petroleum County?
Measured between 28°F hard freezes, Petroleum County sees about 170 frost-free days — roughly Apr 25 through Oct 12, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 16 to Sep 28, about 135 days.
Is the soil safe to grow vegetables in Petroleum County?
The federal record around Petroleum County shows 75 documented sites, mostly Nitrate entries (66), the nearest Nitrate record about 3.3 miles out — 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.
Everything above is measured at Petroleum County's scale — its 4b band and its 170-day season. Your yard writes its own version of Petroleum 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 Petroleum County’s own scale
8 of the readings below were taken at Petroleum County's own scale — its own ~170-day span between 28°F freezes, the 3 most extensive soil series mapped here and 75 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Petroleum County's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Petroleum County's own 28°F hard-freeze dates and its ~170-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Petroleum CountyUSDA NRCS SSURGO
- 75 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 3.3 miles outFederal environmental registers
- Petroleum County's boundary and the 1,059,599 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~170-day seasonGrowable Ground crop-matching engine
- Petroleum County sitting wholly inside the Northwestern Great PlainsUS EPA Level III Ecoregions
- Which agricultural compounds go onto Petroleum 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 Petroleum County — the ~170 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 Petroleum County's 1,059,599 acreswhy one lot differs from the next →
- Which of those 75 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 Petroleum Countyread your own land →