Twin Bridges, Montana, sits in USDA hardiness zone 5a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Crops well matched to these conditions include cabbage, cranberry, lavender, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Even in Twin Bridges, 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 Twin Bridges 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 Twin Bridges — soil, climate, flood, and parcel records. How we handle your address.
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Twin Bridges — the short answer
Twin Bridges, Montana: USDA zone 5a, about 138 days between hard freezes, across 649 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 26
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~138
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 649 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 Twin Bridges's average, not your lot's — a low corner or a tree line moves it. Against Twin Bridges's 138-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Twin Bridges
Each reading below is measured for Twin Bridges itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredTwin Bridges runs about 138 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
MeasuredTwin Bridges 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 Twin Bridges is in
Twin Bridges sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Twin Bridges's own centroid rather than borrowed from Madison County.
What Grows in Twin Bridges
Every plant below cleared Twin Bridges's own zone 5a and its 138-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Twin Bridges?
Almost never — the real question is what to plant next. 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 26 — 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 Twin Bridges
Closest first, within ~10 miles of Twin Bridges. Listing isn't leaking, and distance isn't exposure.
- BOS CHEVRON AND TIRE SERVICEUnderground Storage Tanks · 900 ft
- QWEST TWIN BRIDGES EQUIPMENT BLDGUnderground Storage Tanks · 900 ft
- TWIN BRIDGES AIRPORTUnderground Storage Tanks · 900 ft
- SID SMITH INCUnderground Storage Tanks · 900 ft
- WAGON WHEEL MOTELUnderground Storage Tanks · 1100 ft
- THREE RIVERS QUICK STOPUnderground Storage Tanks · 1100 ft
- TWIN BRIDGES DISTRICT MADISON COUnderground Storage Tanks · 1300 ft
- TWIN BRIDGES PUBLIC SCHOOL DIST 7Underground Storage Tanks · 1400 ft
- R.L. WINSTON ROD COMPANYBrownfields · 1900 ft
- MDOT TWIN BRIDGES SECTION HEADQUARTERSUnderground Storage Tanks · 1.2 mi
- 03S06W35BDAB01Nitrate · 1.3 mi
- 04S06W11AAAD01Nitrate · 2.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Twin Bridges'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 Twin Bridges.
Sources Checked
within ~10 miles of Twin Bridges
Severity Distribution
within ~10 miles of Twin Bridges
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Twin Bridges, Mining runs higher than the national average — 126 sites within ~10 miles of Twin Bridges. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around 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 Twin Bridges
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 Twin Bridges average
Your land is one point inside Twin Bridges
Everything above resolves to Twin Bridges as a whole — one PHZM band and one 28°F frost record, read across 649 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 Twin Bridges Average
Twin Bridges Average
- ●USDA Zones 5a, averaged across Twin Bridges
- ●One soil character for all of Twin Bridges
- ●Frost dates read at Twin Bridges's scale: May 11 to Sep 26
YOUR Parcel
- ✓Your exact zone, not Twin Bridges's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Twin Bridges
Pull a site-specific report for your exact address in Twin Bridges, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Twin Bridges averages can't show:
We read public map data around Twin Bridges — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Twin Bridges average
How we know this about Twin Bridges
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 Twin Bridges’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 Twin Bridges
When does frost risk typically end in Twin Bridges?
The last hard freeze (28°F) in Twin Bridges 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 Twin Bridges?
The first hard freeze (28°F) in Twin Bridges typically arrives around Sep 26, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 12, so the watching starts about Aug 27 — about 138 days after the spring freeze cleared.
How long is the growing season in Twin Bridges?
Measured between 28°F hard freezes, Twin Bridges sees about 138 frost-free days — roughly May 11 through Sep 26, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 1 to Sep 12, about 103 days.
Is the soil safe to grow vegetables in Twin Bridges?
The federal record around Twin Bridges runs heavier than most — 180 documented sites, mostly Mining entries (126), the nearest Underground Storage Tanks record about 0.2 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 Twin Bridges?
With about 138 frost-free days between hard freezes, Twin Bridges 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 166 to 194 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 Twin Bridges's scale — its 5a band and its 138-day season. Your yard writes its own version of Twin Bridges'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 Twin Bridges’s own scale
6 of the readings below were taken at Twin Bridges's own scale — its own ~138-day season between 28°F freezes, the 649 acres it covers and 180 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Twin Bridges's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Twin Bridges's own 28°F hard-freeze dates, about May 11 and Sep 26 and the ~138-day span between themNOAA 1991–2020 Climate Normals
- 180 documented contamination sites on the federal record near Twin Bridges, the closest Underground Storage Tanks record about 0.2 miles out from the town centreFederal environmental registers
- Twin Bridges's boundary and the 649 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~138-day seasonGrowable Ground crop-matching engine
- The ecoregion at Twin Bridges's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Twin Bridges's 649 acres read through its county's SSURGO summaryfrom Madison County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Madison 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 Madison County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Twin Bridges's 649 acreswhy one lot differs from the next →
- Which side of Twin Bridges you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 649 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.2 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 Twin Bridges-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaTwin Bridges sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides