Dewey, Montana, sits in USDA hardiness zone 4a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
A short list that earns its place here — zucchini, cranberry, cilantro, and okra — with any one site's soil, sun, and drainage making the final cut.
Even in Dewey, 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 Dewey 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 Dewey — soil, climate, flood, and parcel records. How we handle your address.
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Dewey — the short answer
Dewey, Montana: USDA zone 4a, about 105 days between hard freezes, across 169 acres of town.
- USDA zone
- 4a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 1
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 14
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~105
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 169 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 Dewey's average, not your lot's — a low corner or a tree line moves it. Against Dewey's 105-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Dewey
Each reading below is measured for Dewey itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredDewey runs about 105 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
MeasuredDewey 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 Dewey is in
Dewey sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Dewey's own centroid rather than borrowed from Beaverhead County.
What Grows in Dewey
Every plant below cleared Dewey's own zone 4a and its 105-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Dewey?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around May 4; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 1 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 14 — long-season crops need about 90 days of runway, quick greens only 30. In a season this compact, fast finishers and cold-hardy greens do the late work, and garlic tucked in before the freeze repays you next summer.
What's on the federal record near Dewey
Closest first, within ~10 miles of Dewey. Listing isn't leaking, and distance isn't exposure.
- Churchill MineMining · 1.1 mi
- BUTTE SILVERBOW WATER DEPTPFAS · 2.0 mi
- Madison MineMining · 2.7 mi
- Mount Fleecer-Jerry Creek AreaMining · 3.7 mi
- Star GroupMining · 3.7 mi
- Monte Cristo MineMining · 3.9 mi
- Cayuga ClaimMining · 3.9 mi
- Helehan ProspectMining · 3.9 mi
- Aurora MineMining · 4.2 mi
- Unknown ShaftMining · 4.3 mi
- Pettingill MineMining · 4.3 mi
- Great Western MineMining · 4.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Dewey'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 Dewey.
Total Sites
63
within ~10 miles of Dewey
Risk Level
High
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
within ~10 miles of Dewey
Severity Distribution
within ~10 miles of Dewey
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Dewey, Mining runs higher than the national average — 54 sites within ~10 miles of Dewey. That's not a problem with your land — it's information about 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Dewey
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 Dewey average
Your land is one point inside Dewey
Everything above resolves to Dewey as a whole — one PHZM band and one 28°F frost record, read across 169 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 Dewey Average
Dewey Average
- ●USDA Zones 4a, averaged across Dewey
- ●One soil character for all of Dewey
- ●Frost dates read at Dewey's scale: Jun 1 to Sep 14
YOUR Parcel
- ✓Your exact zone, not Dewey's 4a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Dewey
Pull a site-specific report for your exact address in Dewey, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Dewey averages can't show:
We read public map data around Dewey — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Dewey average
How we know this about Dewey
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 Dewey’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 Dewey
When does frost risk typically end in Dewey?
The last hard freeze (28°F) in Dewey typically lands around Jun 1, 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 22.
When is the first frost in Dewey?
The first hard freeze (28°F) in Dewey typically arrives around Sep 14, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Aug 31, so the watching starts about Aug 15 — about 105 days after the spring freeze cleared.
How long is the growing season in Dewey?
Measured between 28°F hard freezes, Dewey sees about 105 frost-free days — roughly Jun 1 through Sep 14, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 22 to Aug 31, about 70 days.
Is the soil safe to grow vegetables in Dewey?
The federal record around Dewey runs heavier than most — 63 documented sites, mostly Mining entries (54), the nearest Mining record about 1.1 miles 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 Dewey?
With about 105 frost-free days between hard freezes, Dewey 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 133 to 161 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 1 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Dewey's scale — its 4a band and its 105-day season. Your yard writes its own version of Dewey'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 Dewey’s own scale
6 of the readings below were taken at Dewey's own scale — its own ~105-day season between 28°F freezes, the 169 acres it covers and 63 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Dewey's own USDA hardiness band, zones 4aUSDA PHZM 2023
- Dewey's own 28°F hard-freeze dates, about Jun 1 and Sep 14 and the ~105-day span between themNOAA 1991–2020 Climate Normals
- 63 documented contamination sites on the federal record near Dewey, the closest Mining record about 1.1 miles out from the town centreFederal environmental registers
- Dewey's boundary and the 169 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4a and a ~105-day seasonGrowable Ground crop-matching engine
- The ecoregion at Dewey's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Dewey's 169 acres read through its county's SSURGO summaryfrom Beaverhead County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Beaverhead 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 Beaverhead County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Dewey's 169 acreswhy one lot differs from the next →
- Which side of Dewey you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 169 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Mining record about 1.1 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 Dewey-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaDewey sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides