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

Planting zone for 59025 — Decker, MT

ZIP code 59025 (Decker, Big Horn County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 18 and the first fall frost September 24.

Where ZIP 59025 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostMay 18

First frostSep 24

2012 zone4a

Was 4a on the 2012 map — a full zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Decker, 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 Decker, MT

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 18median — 50% chance of a later frost

Safe for tender plantsJune 2only 10% chance of frost after

First fall frostSeptember 24median — 10% chance by Sep 9

Growing season127 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 5 and returns around October 3.

From the NOAA station Sheridan Field Stn, WY — 18 miles away, elevation 3,750 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 59025

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 6 – Apr 20

SpinachSow outdoors · Apr 6 – Apr 27

Broccoli, cabbageStart indoors · Mar 9 – Mar 23

Broccoli, cabbageTransplant · Apr 27 – May 11

Onion setsPlant outdoors · Apr 20 – May 4

PotatoesPlant outdoors · Apr 27 – May 11

LettuceSow outdoors · Apr 20 – May 4

Carrots, beetsSow outdoors · Apr 27 – May 11

TomatoesStart indoors · Mar 23 – Apr 6

TomatoesTransplant · May 25 – Jun 8

Peppers, eggplantStart indoors · Mar 9 – Mar 23

Peppers, eggplantTransplant · Jun 1 – Jun 15

BeansSow outdoors · May 25 – Jun 8

Sweet cornSow outdoors · May 25 – Jun 8

Cucumbers, squashSow outdoors · May 25 – Jun 8

Fall lettuce, spinachSow outdoors · Jul 30 – Aug 13

GarlicPlant cloves · Sep 10 – Oct 15

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 18) and first fall frost (Sep 24) 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 59025 came on Mar 23 — 16 days earlier than the 1991–2020 average (Apr 8).

average
Apr 82026
Mar 23

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 5a in Montana

548 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Decker, MT.

Soil in Decker, MT

The soil mapped at the center of ZIP 59025 is Thedalund — loam, well drained.

TextureLoama good balance for most vegetables

pH7.5slightly alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Thedalund-Midway complex, rolling.

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 59025; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Decker, MT

Summer high87 °Faverage high, July

Winter low10 °Faverage low, January

Hot days39days a year at 90 °F or more

Freezing nights200nights a year at 32 °F or less

Growing degree days2,157base 50 °F — the season’s usable heat

Longest day15 h 38 mindaylight on June 21

Shortest day8 h 45 mindaylight on December 21

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

Precipitation10.5 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Sheridan Field Stn, WY (18 mi away); precipitation: Decker, MT (9 mi away). 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.

Ranchester, WY · 24 mi

590165a

Busby, MT · 28 mi

828355a

Clearmont, WY · 28 mi

828445a

Wolf, WY · 31 mi

Montana planting zones →

Questions about 59025

What planting zone is ZIP code 59025?

ZIP code 59025 (Decker, MT) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Decker, MT?

The median last spring frost (32 °F) near 59025 is May 18; after June 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sheridan Field Stn station.

When is the first frost in Decker, MT?

The median first fall frost near 59025 is September 24, giving a median frost-free growing season of 127 days.

When should I plant tomatoes in 59025?

Start tomato seeds indoors around Mar 23 – Apr 6 and set transplants outside around May 25 – Jun 8, one to three weeks after the median last frost.

How much rain and snow does 59025 get?

About 10.5 inches of precipitation a year (NOAA 1991–2020 normals, Decker station).

How hot do summers get in Decker, MT?

The average high peaks at 87 °F in July, with about 39 days a year at 90 °F or more.

What kind of soil does 59025 have?

The USDA soil survey maps Thedalund at the center of ZIP 59025: loam, well drained, pH about 7.5 (slightly alkaline).

Did spring come early in Decker, MT in 2026?

Spring leaf-out near 59025 came on Mar 23 in 2026, 16 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Decker, MT?

Long-day onions: the longest day near 59025 is 15 h 38 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59025 change?

Yes. The 2012 USDA map put 59025 in zone 4a; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.