Rocky Boy's Agency, Montana, sits in USDA hardiness zone 4a — 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 Rocky Boy's Agency, 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 Rocky Boy's Agency 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 Rocky Boy's Agency — soil, climate, flood, and parcel records. How we handle your address.
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Rocky Boy's Agency — the short answer
Rocky Boy's Agency, Montana: USDA zone 4a, about 130 days between hard freezes, across 5K acres of town.
- USDA zone
- 4a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 18
- 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
- ~130
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 5K 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 4a is Rocky Boy's Agency's average, not your lot's — a low corner or a tree line moves it. Against Rocky Boy's Agency's 130-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Rocky Boy's Agency
Each reading below is measured for Rocky Boy's Agency itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredRocky Boy's Agency runs about 130 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
MeasuredRocky Boy's Agency sits in USDA hardiness zone 4a.
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 Rocky Boy's Agency is in
Rocky Boy's Agency sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Rocky Boy's Agency's own centroid, and it is not what its county reads: Hill County is mostly Northwestern Glaciated Plains. The wider page above you is answering a different question about different ground.
What Grows in Rocky Boy's Agency
Every plant below cleared Rocky Boy's Agency's own zone 4a and its 130-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Rocky Boy's Agency?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Apr 20; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 18 (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 Rocky Boy's Agency
Closest first, within ~10 miles of Rocky Boy's Agency. Listing isn't leaking, and distance isn't exposure.
- ROCKY BOY ELEMENTARY SCHOOLUnderground Storage Tanks · 2600 ft
- ROCKY BOY AGENCY SHOPUnderground Storage Tanks · 0.8 mi
- OATS ROAD DRUMSSuperfund · 0.9 mi
- VILLAGE GROCERYUnderground Storage Tanks · 1.1 mi
- GRAIN & CATTLE CORPUnderground Storage Tanks · 1.1 mi
- OLD CORNER GROCERYUnderground Storage Tanks · 1.1 mi
- LAMERES STATIONUnderground Storage Tanks · 1.1 mi
- SQUAW BUTTE MICROWAVE SITEUnderground Storage Tanks · 1.1 mi
- ORDEAN SOLBERGUnderground Storage Tanks · 1.1 mi
- FRANK & OREL M SHERERUnderground Storage Tanks · 1.1 mi
- Rocky Boy AreaMining · 6.4 mi
- UnnamedMining · 7.0 mi
4 more sites are on the record inside the same radius. See them on the map
Measured from Rocky Boy's Agency'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 Rocky Boy's Agency.
Total Sites
18
within ~10 miles of Rocky Boy's Agency
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Rocky Boy's Agency
Severity Distribution
within ~10 miles of Rocky Boy's Agency
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •Mine waste leaches heavy metals. Test for lead, arsenic and cadmium before growing food here.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
Check your specific parcel in Rocky Boy's Agency
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 Rocky Boy's Agency average
Your land is one point inside Rocky Boy's Agency
Everything above resolves to Rocky Boy's Agency as a whole — one PHZM band and one 28°F frost record, read across 5K 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 Rocky Boy's Agency Average
Rocky Boy's Agency Average
- ●USDA Zones 4a, averaged across Rocky Boy's Agency
- ●One soil character for all of Rocky Boy's Agency
- ●Frost dates read at Rocky Boy's Agency's scale: May 18 to Sep 25
YOUR Parcel
- ✓Your exact zone, not Rocky Boy's Agency's 4a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Rocky Boy's Agency
Pull a site-specific report for your exact address in Rocky Boy's Agency, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Rocky Boy's Agency averages can't show:
We read public map data around Rocky Boy's Agency — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rocky Boy's Agency average
How we know this about Rocky Boy's Agency
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 Rocky Boy's Agency’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 Rocky Boy's Agency
When does frost risk typically end in Rocky Boy's Agency?
The last hard freeze (28°F) in Rocky Boy's Agency typically lands around May 18, 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 8.
When is the first frost in Rocky Boy's Agency?
The first hard freeze (28°F) in Rocky Boy's Agency 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 130 days after the spring freeze cleared.
How long is the growing season in Rocky Boy's Agency?
Measured between 28°F hard freezes, Rocky Boy's Agency sees about 130 frost-free days — roughly May 18 through Sep 25, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 8 to Sep 11, about 95 days.
Is the soil safe to grow vegetables in Rocky Boy's Agency?
The federal record around Rocky Boy's Agency is a meaningful one — 18 documented sites, mostly Underground Storage Tanks entries (11), the nearest Underground Storage Tanks record about 0.5 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 Rocky Boy's Agency?
With about 130 frost-free days between hard freezes, Rocky Boy's Agency 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 158 to 186 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 18 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Rocky Boy's Agency's scale — its 4a band and its 130-day season. Your yard writes its own version of Rocky Boy's Agency'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 Rocky Boy's Agency’s own scale
6 of the readings below were taken at Rocky Boy's Agency's own scale — its own ~130-day season between 28°F freezes, the 5,487 acres it covers and 18 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Rocky Boy's Agency's own USDA hardiness band, zones 4aUSDA PHZM 2023
- Rocky Boy's Agency's own 28°F hard-freeze dates, about May 18 and Sep 25 and the ~130-day span between themNOAA 1991–2020 Climate Normals
- 18 documented contamination sites on the federal record near Rocky Boy's Agency, the closest Underground Storage Tanks record about 0.5 miles out from the town centreFederal environmental registers
- Rocky Boy's Agency's boundary and the 5,487 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4a and a ~130-day seasonGrowable Ground crop-matching engine
- Rocky Boy's Agency sits in the Middle Rockies — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Rocky Boy's Agency's 5,487 acres read through its county's SSURGO summaryfrom Hill County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Hill 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 Hill County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Rocky Boy's Agency's 5,487 acreswhy one lot differs from the next →
- Which side of Rocky Boy's Agency you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 5,487 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.5 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 Rocky Boy's Agency-wide figureread your own land →
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