Mammoth, Montana, sits in USDA hardiness zone 5a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Growers here do well with pumpkin, cranberry, lavender, and zucchini — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Even in Mammoth, 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 Mammoth 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 Mammoth — soil, climate, flood, and parcel records. How we handle your address.
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Mammoth — the short answer
Mammoth, Montana: USDA zone 5a, about 105 days between hard freezes, across 224 acres of town.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 5
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~105
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 224 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 Mammoth's average, not your lot's — a low corner or a tree line moves it. Against Mammoth's 105-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Mammoth
Each reading below is measured for Mammoth itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredMammoth 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
MeasuredMammoth 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 Mammoth is in
Mammoth sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Mammoth's own centroid rather than borrowed from Madison County.
What Grows in Mammoth
Every plant below cleared Mammoth's own zone 5a and its 105-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Mammoth?
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 8; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 5 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 18 — 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 Mammoth
Closest first, within ~10 miles of Mammoth. Listing isn't leaking, and distance isn't exposure.
- Mammoth MineMining · 1200 ft
- MammothMining · 1900 ft
- Atlantic and Pacific MineMining · 2.2 mi
- Bozeman MineMining · 2.4 mi
- White Pine MineMining · 2.5 mi
- Ben Harrison FractionMining · 2.6 mi
- Lone Wolf and Cataract MineMining · 2.7 mi
- Mountain CliffMining · 2.8 mi
- Mountain Meadow MineMining · 2.9 mi
- Boss Tweed and ClipperMining · 2.9 mi
- Boss Tweed MineMining · 2.9 mi
- Antelope-Pony DistrictMining · 3.0 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Mammoth'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 Mammoth.
Sources Checked
within ~10 miles of Mammoth
Severity Distribution
within ~10 miles of Mammoth
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Mammoth, Mining runs higher than the national average — 112 sites within ~10 miles of Mammoth. 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Mammoth
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 Mammoth average
Your land is one point inside Mammoth
Everything above resolves to Mammoth as a whole — one PHZM band and one 28°F frost record, read across 224 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 Mammoth Average
Mammoth Average
- ●USDA Zones 5a, averaged across Mammoth
- ●One soil character for all of Mammoth
- ●Frost dates read at Mammoth's scale: Jun 5 to Sep 18
YOUR Parcel
- ✓Your exact zone, not Mammoth's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Mammoth
Pull a site-specific report for your exact address in Mammoth, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Mammoth averages can't show:
We read public map data around Mammoth — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Mammoth average
How we know this about Mammoth
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 Mammoth’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 Mammoth
When does frost risk typically end in Mammoth?
The last hard freeze (28°F) in Mammoth typically lands around Jun 5, 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 26.
When is the first frost in Mammoth?
The first hard freeze (28°F) in Mammoth typically arrives around Sep 18, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 4, so the watching starts about Aug 19 — about 105 days after the spring freeze cleared.
How long is the growing season in Mammoth?
Measured between 28°F hard freezes, Mammoth sees about 105 frost-free days — roughly Jun 5 through Sep 18, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 26 to Sep 4, about 70 days.
Is the soil safe to grow vegetables in Mammoth?
The federal record around Mammoth runs heavier than most — 125 documented sites, mostly Mining entries (112), the nearest Mining 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 Mammoth?
With about 105 frost-free days between hard freezes, Mammoth 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 5 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Mammoth's scale — its 5a band and its 105-day season. Your yard writes its own version of Mammoth'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 Mammoth’s own scale
6 of the readings below were taken at Mammoth's own scale — its own ~105-day season between 28°F freezes, the 224 acres it covers and 125 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Mammoth's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Mammoth's own 28°F hard-freeze dates, about Jun 5 and Sep 18 and the ~105-day span between themNOAA 1991–2020 Climate Normals
- 125 documented contamination sites on the federal record near Mammoth, the closest Mining record about 0.2 miles out from the town centreFederal environmental registers
- Mammoth's boundary and the 224 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~105-day seasonGrowable Ground crop-matching engine
- The ecoregion at Mammoth's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Mammoth's 224 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 Mammoth's 224 acreswhy one lot differs from the next →
- Which side of Mammoth you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 224 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Mining 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 Mammoth-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaMammoth sits outside our named growing regions, so Montana as a whole is its closest context here.
Nearby growing guides