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

Planting zone for 59031 — Garryowen, MT

ZIP code 59031 (Garryowen, Big Horn County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 13 and the first fall frost September 29.

Where ZIP 59031 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 frostMay 13

First frostSep 29

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 Garryowen, 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 Garryowen, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 13median — 50% chance of a later frost

Safe for tender plantsMay 26only 10% chance of frost after

First fall frostSeptember 29median — 10% chance by Sep 14

Growing season135 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 1 and returns around October 7.

From the NOAA station Hardin, MT — 20 miles away, elevation 2,881 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 59031

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 1 – Apr 15

SpinachSow outdoors · Apr 1 – Apr 22

Broccoli, cabbageStart indoors · Mar 4 – Mar 18

Broccoli, cabbageTransplant · Apr 22 – May 6

Onion setsPlant outdoors · Apr 15 – Apr 29

PotatoesPlant outdoors · Apr 22 – May 6

LettuceSow outdoors · Apr 15 – Apr 29

Carrots, beetsSow outdoors · Apr 22 – May 6

TomatoesStart indoors · Mar 18 – Apr 1

TomatoesTransplant · May 20 – Jun 3

Peppers, eggplantStart indoors · Mar 4 – Mar 18

Peppers, eggplantTransplant · May 27 – Jun 10

BeansSow outdoors · May 20 – Jun 3

Sweet cornSow outdoors · May 20 – Jun 3

Cucumbers, squashSow outdoors · May 20 – Jun 3

Fall lettuce, spinachSow outdoors · Aug 4 – Aug 18

GarlicPlant cloves · Sep 15 – Oct 20

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 13) and first fall frost (Sep 29) 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 59031 came on Mar 16 — 20 days earlier than the 1991–2020 average (Apr 5).

average
Apr 52026
Mar 16

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 Garryowen, MT.

Soil in Garryowen, MT

The soil mapped at the center of ZIP 59031 is Marias — clay, well drained.

TextureClayholds water and nutrients; slow to drain and warm up

pH7.9alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.25%low — add compost

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Marias clay, 8 to 15 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 59031; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Garryowen, MT

Summer high91 °Faverage high, July

Winter low11 °Faverage low, January

Hot days52days a year at 90 °F or more

Freezing nights166nights a year at 32 °F or less

Growing degree days2,597base 50 °F — the season’s usable heat

Longest day15 h 41 mindaylight on June 21

Shortest day8 h 42 mindaylight on December 21

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

Precipitation13.8 inper year, rain and melted snow

Snowfall28 inper year; 40 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

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

Nearby ZIP codes

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

590224b

Crow Agency, MT · 7 mi

590505a

Lodge Grass, MT · 17 mi

590165a

Busby, MT · 21 mi

590755a

Saint Xavier, MT · 24 mi

Fort Smith, MT · 31 mi

590104b

Bighorn, MT · 32 mi

Montana planting zones →

Questions about 59031

What planting zone is ZIP code 59031?

ZIP code 59031 (Garryowen, 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 Garryowen, MT?

The median last spring frost (32 °F) near 59031 is May 13; after May 26 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Hardin station.

When is the first frost in Garryowen, MT?

The median first fall frost near 59031 is September 29, giving a median frost-free growing season of 135 days.

When should I plant tomatoes in 59031?

Start tomato seeds indoors around Mar 18 – Apr 1 and set transplants outside around May 20 – Jun 3, one to three weeks after the median last frost.

How much rain and snow does 59031 get?

About 13.8 inches of precipitation a year and 28 inches of snowfall (NOAA 1991–2020 normals, Hardin station).

How hot do summers get in Garryowen, MT?

The average high peaks at 91 °F in July, with about 52 days a year at 90 °F or more.

What kind of soil does 59031 have?

The USDA soil survey maps Marias at the center of ZIP 59031: clay, well drained, pH about 7.9 (alkaline).

Did spring come early in Garryowen, MT in 2026?

Spring leaf-out near 59031 came on Mar 16 in 2026, 20 days earlier than the 1991–2020 average (Apr 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Garryowen, MT?

Long-day onions: the longest day near 59031 is 15 h 41 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59031 change?

Yes. The 2012 USDA map put 59031 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.