Helena Valley Northwest, Montana, sits in USDA hardiness zone 4b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Well-matched crops include cabbage, cranberry, turkish rocket, and collard greens, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Even in Helena Valley Northwest, 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 Helena Valley Northwest 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 Helena Valley Northwest — soil, climate, flood, and parcel records. How we handle your address.
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Helena Valley Northwest — the short answer
Helena Valley Northwest, Montana: USDA zone 4b, about 159 days between hard freezes, across 10K acres of town.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 3
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 9
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~159
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 10K 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 4b is Helena Valley Northwest's average, not your lot's — a low corner or a tree line moves it. Against Helena Valley Northwest's 159-day season, see what your own ground reads.
Your town runs its own season
Helena Valley Northwest's own 30-year record measures about 159 days between 28°F killing freezes — 35 days longer than Lewis and Clark County's ~124. Both are measured records, not estimates.
That gap is the whole reason a county average can mislead here. Plant against Helena Valley Northwest's ~159-day season rather than the county figure — and the sun, slope and cold-air drainage on your specific lot move it again.
NOAA Regional Climate Centers ACIS (1991–2020), 30-year daily minimum record. Both figures are measured records — this town’s own and its county’s. A town with no record of its own is absent here rather than estimated.
Soil varies lot by lot — soil types explained.
What this means for growing in Helena Valley Northwest
Each reading below is measured for Helena Valley Northwest itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredHelena Valley Northwest runs about 159 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredHelena Valley Northwest sits in USDA hardiness zone 4b.
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 Helena Valley Northwest is in
Helena Valley Northwest sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Helena Valley Northwest's own centroid rather than borrowed from Lewis and Clark County.
What Grows in Helena Valley Northwest
Every plant below cleared Helena Valley Northwest's own zone 4b and its 159-day season. Each card opens that plant's Montana profile. How we score.
Is it too late to plant in Helena Valley Northwest?
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 5; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 3 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 9 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
What's on the federal record near Helena Valley Northwest
Closest first, within ~10 miles of Helena Valley Northwest. Listing isn't leaking, and distance isn't exposure.
- 11N04W12CDDD01Nitrate · 0.7 mi
- AL ROSE AUTO WRECKINGBrownfields · 0.8 mi
- 11N04W01DADB01Nitrate · 1.0 mi
- 11N03W07BDBB01Nitrate · 1.0 mi
- 11N04W13AAAD01Nitrate · 1.1 mi
- 11N03W18BCCB01Nitrate · 1.4 mi
- 11N04W10AABA01Nitrate · 1.4 mi
- FREDDY L & BARBARA J SHEPHERDUnderground Storage Tanks · 1.5 mi
- Miljour-Violet Jane MineMining · 1.6 mi
- 11N04W13CCC 01Nitrate · 1.7 mi
- 11N04W13CCCC01Nitrate · 1.7 mi
- 11N04W14DCCA01Nitrate · 1.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Helena Valley Northwest'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 Helena Valley Northwest.
Total Sites
968
within ~10 miles of Helena Valley Northwest
Risk Level
High
Highest-severity
5 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Helena Valley Northwest
Severity Distribution
within ~10 miles of Helena Valley Northwest
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Helena Valley Northwest, two things run higher than the national average within ~10 miles of Helena Valley Northwest — Nitrate (600 sites) and Mining (84 sites). That's not a problem with your land — it's information about it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
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 well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Helena Valley Northwest
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 Helena Valley Northwest average
Your land is one point inside Helena Valley Northwest
Everything above resolves to Helena Valley Northwest as a whole — and this is a town whose own 30-year record already runs a season its county’s does not. Your parcel sits at one point inside even that. 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 Helena Valley Northwest Average
Helena Valley Northwest Average
- ●USDA Zones 4b, averaged across Helena Valley Northwest
- ●One soil character for all of Helena Valley Northwest
- ●Frost dates read at Helena Valley Northwest's scale: May 3 to Oct 9
YOUR Parcel
- ✓Your exact zone, not Helena Valley Northwest's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Helena Valley Northwest
Pull a site-specific report for your exact address in Helena Valley Northwest, Montana — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Helena Valley Northwest averages can't show:
We read public map data around Helena Valley Northwest — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Helena Valley Northwest average
How we know this about Helena Valley Northwest
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 Helena Valley Northwest’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 Helena Valley Northwest
When does frost risk typically end in Helena Valley Northwest?
The last hard freeze (28°F) in Helena Valley Northwest typically lands around May 3, 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 May 24.
When is the first frost in Helena Valley Northwest?
The first hard freeze (28°F) in Helena Valley Northwest typically arrives around Oct 9, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 25, so the watching starts about Sep 9 — about 159 days after the spring freeze cleared.
How long is the growing season in Helena Valley Northwest?
Measured between 28°F hard freezes, Helena Valley Northwest sees about 159 frost-free days — roughly May 3 through Oct 9, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 24 to Sep 25, about 124 days.
Is the soil safe to grow vegetables in Helena Valley Northwest?
The federal record around Helena Valley Northwest runs heavier than most — 968 documented sites, mostly Nitrate entries (600), the nearest Nitrate record about 0.7 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 I protect my plants from frost in Helena Valley Northwest?
From about Sep 9 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 9 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 9. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Helena Valley Northwest's scale — its 4b band and its 159-day season. Your yard writes its own version of Helena Valley Northwest'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 Helena Valley Northwest’s own scale
6 of the readings below were taken at Helena Valley Northwest's own scale — its own ~159-day season between 28°F freezes, the 10,481 acres it covers and 968 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Helena Valley Northwest's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Helena Valley Northwest's own 28°F hard-freeze dates, about May 3 and Oct 9 and the ~159-day span between themNOAA 1991–2020 Climate Normals
- 968 documented contamination sites on the federal record near Helena Valley Northwest, the closest Nitrate record about 0.7 miles out from the town centreFederal environmental registers
- Helena Valley Northwest's boundary and the 10,481 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~159-day seasonGrowable Ground crop-matching engine
- The ecoregion at Helena Valley Northwest's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Helena Valley Northwest's 10,481 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 Helena Valley Northwest's 10,481 acreswhy one lot differs from the next →
- Which side of Helena Valley Northwest you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 10,481 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 0.7 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 Helena Valley Northwest-wide figureread your own land →
More in Montana
Wider growing context
What grows across MontanaHelena Valley Northwest sits outside our named growing regions, so Montana as a whole is its closest context here.