Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 59601 — Helena, MT

ZIP code 59601 (Helena, Lewis and Clark County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is June 4 and the first fall frost September 14.

Where ZIP 59601 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone4b−25 to −20 °F
Coldest night−31.7 to −28.9 °C
Last frostJun 4
First frostSep 14
2012 zone4b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Helena, MT…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Helena, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJune 4median — 50% chance of a later frost
Safe for tender plantsJune 18only 10% chance of frost after
First fall frostSeptember 14median — 10% chance by Aug 30
Growing season100 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 14 and returns around September 26.

From the NOAA station Austin 1 W, MT — 9 miles away, elevation 4,853 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 59601

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 23 – May 7
SpinachSow outdoors · Apr 23 – May 14
Broccoli, cabbageStart indoors · Mar 26 – Apr 9
Broccoli, cabbageTransplant · May 14 – May 28
Onion setsPlant outdoors · May 7 – May 21
PotatoesPlant outdoors · May 14 – May 28
LettuceSow outdoors · May 7 – May 21
Carrots, beetsSow outdoors · May 14 – May 28
TomatoesStart indoors · Apr 9 – Apr 23
TomatoesTransplant · Jun 11 – Jun 25
Peppers, eggplantStart indoors · Mar 26 – Apr 9
Peppers, eggplantTransplant · Jun 18 – Jul 2
BeansSow outdoors · Jun 11 – Jun 25
Sweet cornSow outdoors · Jun 11 – Jun 25
Cucumbers, squashSow outdoors · Jun 11 – Jun 25
Fall lettuce, spinachSow outdoors · Jul 20 – Aug 3
GarlicPlant cloves · Aug 31 – Oct 5
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 4) and first fall frost (Sep 14) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 59601 came on Apr 16 — 12 days earlier than the 1991–2020 average (Apr 28).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 4b in Montana

506 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 23

American elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °FDouglas-fir200 ft · blooms mid spring · medium shade tolerance · to −33 °Feastern cottonwood190 ft · blooms spring · high shade tolerance · to −43 °F

Shrubs 87

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °Falderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °F

Wildflowers & perennials 229

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °F

Grasses 155

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 3

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Helena, MT.

Soil in Helena, MT

The soil mapped at the center of ZIP 59601 is Typic Cryoboralfs — slightly decomposed plant material.

TextureSlightly decomposed plant materialtop layer
pH6.5neutral; most vegetables like 6.0–7.0
Organic matter50%high
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Typic Cryoboralfs and Mollic Cryoboralfs, steep.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 59601; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Helena, MT

Summer high78 °Faverage high, July
Winter low13 °Faverage low, January
Hot days4days a year at 90 °F or more
Freezing nights204nights a year at 32 °F or less
Growing degree days1,244base 50 °F — the season’s usable heat
Longest day15 h 50 mindaylight on June 21
Shortest day8 h 34 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation24.1 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 30 °F, low 13 °F 30°13° JanFebruary: average high 32 °F, low 13 °F 32°13° FebMarch: average high 42 °F, low 19 °F 42°19° MarApril: average high 50 °F, low 26 °F 50°26° AprMay: average high 60 °F, low 35 °F 60°35° MayJune: average high 68 °F, low 42 °F 68°42° JunJuly: average high 78 °F, low 49 °F 78°49° JulAugust: average high 78 °F, low 47 °F 78°47° AugSeptember: average high 67 °F, low 39 °F 67°39° SepOctober: average high 51 °F, low 30 °F 51°30° OctNovember: average high 37 °F, low 20 °F 37°20° NovDecember: average high 29 °F, low 13 °F 29°13° Dec

Precipitation by month inches

0″1″2″3″4″January: 1.46 in precipitation 1.5 JanFebruary: 1.57 in precipitation 1.6 FebMarch: 1.72 in precipitation 1.7 MarApril: 2.53 in precipitation 2.5 AprMay: 3.43 in precipitation 3.4 MayJune: 3.27 in precipitation 3.3 JunJuly: 1.68 in precipitation 1.7 JulAugust: 1.49 in precipitation 1.5 AugSeptember: 1.63 in precipitation 1.6 SepOctober: 1.97 in precipitation 2.0 OctNovember: 1.73 in precipitation 1.7 NovDecember: 1.62 in precipitation 1.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Austin 1 W, MT (9 mi away); precipitation: Frohner Meadow, MT (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

3 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

596364b
Fort Harrison, MT · 7 mi
596235a
Helena, MT · 9 mi
596205a
Helena, MT · 9 mi
596245a
Helena, MT · 9 mi
596264b
Helena, MT · 9 mi
596344b
Clancy, MT · 10 mi
597284b
Elliston, MT · 11 mi
596044b
Helena, MT · 14 mi

All 7 ZIP codes in Helena → · Montana planting zones →

Questions about 59601

What planting zone is ZIP code 59601?

ZIP code 59601 (Helena, MT) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Helena, MT?

The median last spring frost (32 °F) near 59601 is June 4; after June 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Austin 1 W station.

When is the first frost in Helena, MT?

The median first fall frost near 59601 is September 14, giving a median frost-free growing season of 100 days.

When should I plant tomatoes in 59601?

Start tomato seeds indoors around Apr 9 – Apr 23 and set transplants outside around Jun 11 – Jun 25, one to three weeks after the median last frost.

How much rain and snow does 59601 get?

About 24.1 inches of precipitation a year (NOAA 1991–2020 normals, Frohner Meadow station).

How hot do summers get in Helena, MT?

The average high peaks at 78 °F in July, with about 4 days a year at 90 °F or more.

What kind of soil does 59601 have?

The USDA soil survey maps Typic Cryoboralfs at the center of ZIP 59601: slightly decomposed plant material, pH about 6.5 (neutral).

Did spring come early in Helena, MT in 2026?

Spring leaf-out near 59601 came on Apr 16 in 2026, 12 days earlier than the 1991–2020 average (Apr 28), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Helena, MT?

Long-day onions: the longest day near 59601 is 15 h 50 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).