Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 59421 — Cascade, MT

ZIP code 59421 (Cascade, Cascade 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 12.

Where ZIP 59421 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 12

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 Cascade, 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 Cascade, 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 22only 10% chance of frost after

First fall frostSeptember 12median — 10% chance by Aug 26

Growing season98 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 16 and returns around September 27.

From the NOAA station Adel, MT — 4 miles away, elevation 5,017 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 59421

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 18 – Aug 1

GarlicPlant cloves · Aug 29 – Oct 3

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 4) and first fall frost (Sep 12) 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 59421 came on Apr 27 — 7 days earlier than the 1991–2020 average (May 4).

average
May 42026
Apr 27

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.

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 Cascade, MT.

Soil in Cascade, MT

The soil mapped at the center of ZIP 59421 is Loberg — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter75%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Loberg-Cheadle complex, 20 to 60 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 59421; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cascade, MT

Summer high78 °Faverage high, July

Winter low14 °Faverage low, January

Hot days3days a year at 90 °F or more

Freezing nights191nights a year at 32 °F or less

Growing degree days1,204base 50 °F — the season’s usable heat

Longest day15 h 54 mindaylight on June 21

Shortest day8 h 30 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation14.9 inper year, rain and melted snow

Snowfall63 inper year

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Adel, MT (4 mi away); precipitation: Cascade 20 Sse, MT (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

594054b

Great Falls, MT · 23 mi

596484b

Wolf Creek, MT · 24 mi

Sun River, MT · 27 mi

594774b

Simms, MT · 29 mi

594724b

Sand Coulee, MT · 29 mi

594804b

Stockett, MT · 30 mi

Montana planting zones →

Questions about 59421

What planting zone is ZIP code 59421?

ZIP code 59421 (Cascade, 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 Cascade, MT?

The median last spring frost (32 °F) near 59421 is June 4; after June 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Adel station.

When is the first frost in Cascade, MT?

The median first fall frost near 59421 is September 12, giving a median frost-free growing season of 98 days.

When should I plant tomatoes in 59421?

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 59421 get?

About 14.9 inches of precipitation a year and 63 inches of snowfall (NOAA 1991–2020 normals, Cascade 20 Sse station).

How hot do summers get in Cascade, MT?

The average high peaks at 78 °F in July, with about 3 days a year at 90 °F or more.

What kind of soil does 59421 have?

The USDA soil survey maps Loberg at the center of ZIP 59421: slightly decomposed plant material, well drained, pH about 5.0 (strongly acidic).

Did spring come early in Cascade, MT in 2026?

Spring leaf-out near 59421 came on Apr 27 in 2026, 7 days earlier than the 1991–2020 average (May 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Cascade, MT?

Long-day onions: the longest day near 59421 is 15 h 54 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59421 change?

Yes. The 2012 USDA map put 59421 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.