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

Planting zone for 59403 — Great Falls, MT

ZIP code 59403 (Great Falls, Cascade County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 6 and the first fall frost October 1.

Where ZIP 59403 is

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 frostMay 6
First frostOct 1
2012 zone4a

Was 4a on the 2012 map — half a zone warmer now. 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 Great Falls, 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 Great Falls, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 6median — 50% chance of a later frost
Safe for tender plantsMay 19only 10% chance of frost after
First fall frostOctober 1median — 10% chance by Sep 17
Growing season147 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 24 and returns around October 11.

From the NOAA station Great Falls 16st, MT — within 1 mile, elevation 3,504 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 59403

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 25 – Apr 8
SpinachSow outdoors · Mar 25 – Apr 15
Broccoli, cabbageStart indoors · Feb 25 – Mar 11
Broccoli, cabbageTransplant · Apr 15 – Apr 29
Onion setsPlant outdoors · Apr 8 – Apr 22
PotatoesPlant outdoors · Apr 15 – Apr 29
LettuceSow outdoors · Apr 8 – Apr 22
Carrots, beetsSow outdoors · Apr 15 – Apr 29
TomatoesStart indoors · Mar 11 – Mar 25
TomatoesTransplant · May 13 – May 27
Peppers, eggplantStart indoors · Feb 25 – Mar 11
Peppers, eggplantTransplant · May 20 – Jun 3
BeansSow outdoors · May 13 – May 27
Sweet cornSow outdoors · May 13 – May 27
Cucumbers, squashSow outdoors · May 13 – May 27
Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20
GarlicPlant cloves · Sep 17 – Oct 22
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 6) and first fall frost (Oct 1) 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 59403 came on Mar 5 — 33 days earlier than the 1991–2020 average (Apr 7).

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 Great Falls, MT.

Soil in Great Falls, MT

The soil mapped at the center of ZIP 59403 is Tally — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH7.0neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupAwater soaks in fast
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Tally fine sandy loam, 0 to 2 percent slopes.

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 59403; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Great Falls, MT

Summer high86 °Faverage high, July
Winter low18 °Faverage low, January
Hot days25days a year at 90 °F or more
Freezing nights143nights a year at 32 °F or less
Growing degree days2,214base 50 °F — the season’s usable heat
Longest day15 h 58 mindaylight on June 21
Shortest day8 h 26 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation15.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 37 °F, low 18 °F 37°18° JanFebruary: average high 39 °F, low 19 °F 39°19° FebMarch: average high 48 °F, low 25 °F 48°25° MarApril: average high 58 °F, low 33 °F 58°33° AprMay: average high 67 °F, low 42 °F 67°42° MayJune: average high 75 °F, low 50 °F 75°50° JunJuly: average high 86 °F, low 55 °F 86°55° JulAugust: average high 84 °F, low 53 °F 84°53° AugSeptember: average high 73 °F, low 45 °F 73°45° SepOctober: average high 59 °F, low 36 °F 59°36° OctNovember: average high 45 °F, low 26 °F 45°26° NovDecember: average high 37 °F, low 20 °F 37°20° Dec

Precipitation by month inches

0″1″2″3″January: 0.61 in precipitation 0.6 JanFebruary: 0.58 in precipitation 0.6 FebMarch: 0.63 in precipitation 0.6 MarApril: 1.79 in precipitation 1.8 AprMay: 2.66 in precipitation 2.7 MayJune: 2.74 in precipitation 2.7 JunJuly: 1.34 in precipitation 1.3 JulAugust: 1.30 in precipitation 1.3 AugSeptember: 1.39 in precipitation 1.4 SepOctober: 1.13 in precipitation 1.1 OctNovember: 0.70 in precipitation 0.7 NovDecember: 0.56 in precipitation 0.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Great Falls 16st, MT (within 1 mile); precipitation: Great Falls 16st, MT (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

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

594014b
Great Falls, MT · 1 mi
594144b
Black Eagle, MT · 3 mi
594064b
Great Falls, MT · 9 mi
594044b
Great Falls, MT · 9 mi
594724b
Sand Coulee, MT · 12 mi
594854a
Ulm, MT · 13 mi
594054b
Great Falls, MT · 15 mi
594404b
Floweree, MT · 16 mi

All 5 ZIP codes in Great Falls → · Montana planting zones →

Questions about 59403

What planting zone is ZIP code 59403?

ZIP code 59403 (Great Falls, 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 Great Falls, MT?

The median last spring frost (32 °F) near 59403 is May 6; after May 19 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Great Falls 16st station.

When is the first frost in Great Falls, MT?

The median first fall frost near 59403 is October 1, giving a median frost-free growing season of 147 days.

When should I plant tomatoes in 59403?

Start tomato seeds indoors around Mar 11 – Mar 25 and set transplants outside around May 13 – May 27, one to three weeks after the median last frost.

How much rain and snow does 59403 get?

About 15.4 inches of precipitation a year (NOAA 1991–2020 normals, Great Falls 16st station).

How hot do summers get in Great Falls, MT?

The average high peaks at 86 °F in July, with about 25 days a year at 90 °F or more.

What kind of soil does 59403 have?

The USDA soil survey maps Tally at the center of ZIP 59403: fine sandy loam, well drained, pH about 7.0 (neutral).

Did spring come early in Great Falls, MT in 2026?

Spring leaf-out near 59403 came on Mar 5 in 2026, 33 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Great Falls, MT?

Long-day onions: the longest day near 59403 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59403 change?

Yes. The 2012 USDA map put 59403 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.