Unionville, Montana, sits in USDA hardiness zone 5a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Even in Unionville, 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 Unionville 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 Unionville — soil, climate, flood, and parcel records. How we handle your address.
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Unionville — the short answer
Unionville, Montana: USDA zone 5a, about 139 days between hard freezes, across 820 acres of town.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 11
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 27
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~139
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 820 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 5a is Unionville's average, not your lot's — a low corner or a tree line moves it. Against Unionville's 139-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Unionville
Each reading below is measured for Unionville itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredUnionville runs about 139 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
MeasuredUnionville sits in USDA hardiness zone 5a.
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 Unionville is in
Unionville sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Unionville's own centroid rather than borrowed from Lewis and Clark County.
What Grows in Unionville
Every plant below cleared Unionville's own zone 5a and its 139-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Unionville?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 13; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 11 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 27 — long-season crops need about 90 days of runway, quick greens only 30. Short seasons reward decisiveness — quick-maturing varieties late, hardy greens under cover, and next year’s garlic in the ground before it closes.
What's on the federal record near Unionville
Closest first, within ~10 miles of Unionville. Listing isn't leaking, and distance isn't exposure.
- Whitlatch-Union MineMining · 2200 ft
- Gray Rock MineMining · 0.6 mi
- Independent MineMining · 0.6 mi
- Blue Bird MineMining · 0.7 mi
- Spring Hill MineMining · 0.8 mi
- Helena DistrictMining · 0.8 mi
- SouvenirMining · 0.9 mi
- Sky MineMining · 1.4 mi
- San JuanMining · 1.6 mi
- BILL SCHROTHUnderground Storage Tanks · 1.9 mi
- Occidental ClaimMining · 2.2 mi
- Last Chance Gulch PlacerMining · 2.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Unionville'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 Unionville.
Sources Checked
within ~10 miles of Unionville
Severity Distribution
within ~10 miles of Unionville
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Unionville, two things run higher than the national average within ~10 miles of Unionville — Mining (212 sites) and Nitrate (520 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Unionville
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 Unionville average
Your land is one point inside Unionville
Everything above resolves to Unionville as a whole — one PHZM band and one 28°F frost record, read across 820 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 Unionville Average
Unionville Average
- ●USDA Zones 5a, averaged across Unionville
- ●One soil character for all of Unionville
- ●Frost dates read at Unionville's scale: May 11 to Sep 27
YOUR Parcel
- ✓Your exact zone, not Unionville's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Unionville
Pull a site-specific report for your exact address in Unionville, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Unionville averages can't show:
We read public map data around Unionville — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Unionville average
How we know this about Unionville
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 Unionville’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 Unionville
When does frost risk typically end in Unionville?
The last hard freeze (28°F) in Unionville typically lands around May 11, 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 1.
When is the first frost in Unionville?
The first hard freeze (28°F) in Unionville typically arrives around Sep 27, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 13, so the watching starts about Aug 28 — about 139 days after the spring freeze cleared.
How long is the growing season in Unionville?
Measured between 28°F hard freezes, Unionville sees about 139 frost-free days — roughly May 11 through Sep 27, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 1 to Sep 13, about 104 days.
Is the soil safe to grow vegetables in Unionville?
The federal record around Unionville runs heavier than most — 1,081 documented sites, mostly Nitrate entries (520), the nearest Mining record about 0.4 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 Unionville?
With about 139 frost-free days between hard freezes, Unionville 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 167 to 195 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 11 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Unionville's scale — its 5a band and its 139-day season. Your yard writes its own version of Unionville'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 Unionville’s own scale
6 of the readings below were taken at Unionville's own scale — its own ~139-day season between 28°F freezes, the 820 acres it covers and 1,081 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Unionville's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Unionville's own 28°F hard-freeze dates, about May 11 and Sep 27 and the ~139-day span between themNOAA 1991–2020 Climate Normals
- 1,081 documented contamination sites on the federal record near Unionville, the closest Mining record about 0.4 miles out from the town centreFederal environmental registers
- Unionville's boundary and the 820 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~139-day seasonGrowable Ground crop-matching engine
- The ecoregion at Unionville's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Unionville's 820 acres read through its county's SSURGO summaryfrom Lewis and Clark County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Lewis and Clark 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 Lewis and Clark County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Unionville's 820 acreswhy one lot differs from the next →
- Which side of Unionville you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 820 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Mining record about 0.4 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 Unionville-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaUnionville sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides