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

Planting zone for 59010 — Bighorn, MT

ZIP code 59010 (Bighorn, Treasure County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 26 and the first fall frost September 16.

Where ZIP 59010 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 26

First frostSep 16

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 Bighorn, 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 Bighorn, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 26median — 50% chance of a later frost

Safe for tender plantsJune 13only 10% chance of frost after

First fall frostSeptember 16median — 10% chance by Sep 1

Growing season111 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 14 and returns around September 27.

From the NOAA station Hysham 25 Sse, MT — 8 miles away, elevation 3,101 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 59010

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 14 – Apr 28

SpinachSow outdoors · Apr 14 – May 5

Broccoli, cabbageStart indoors · Mar 17 – Mar 31

Broccoli, cabbageTransplant · May 5 – May 19

Onion setsPlant outdoors · Apr 28 – May 12

PotatoesPlant outdoors · May 5 – May 19

LettuceSow outdoors · Apr 28 – May 12

Carrots, beetsSow outdoors · May 5 – May 19

TomatoesStart indoors · Mar 31 – Apr 14

TomatoesTransplant · Jun 2 – Jun 16

Peppers, eggplantStart indoors · Mar 17 – Mar 31

Peppers, eggplantTransplant · Jun 9 – Jun 23

BeansSow outdoors · Jun 2 – Jun 16

Sweet cornSow outdoors · Jun 2 – Jun 16

Cucumbers, squashSow outdoors · Jun 2 – Jun 16

Fall lettuce, spinachSow outdoors · Jul 22 – Aug 5

GarlicPlant cloves · Sep 2 – Oct 7

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 26) and first fall frost (Sep 16) 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 59010 came on Mar 16 — 22 days earlier than the 1991–2020 average (Apr 7).

average
Apr 72026
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 Bighorn, MT.

Soil in Bighorn, MT

The soil mapped at the center of ZIP 59010 is Midway — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up

pH7.2neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter0.75%low — add compost

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Midway-Bainville complex.

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 59010; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Bighorn, MT

Summer high88 °Faverage high, July

Winter low9 °Faverage low, January

Hot days39days a year at 90 °F or more

Freezing nights194nights a year at 32 °F or less

Growing degree days2,114base 50 °F — the season’s usable heat

Longest day15 h 45 mindaylight on June 21

Shortest day8 h 38 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

Snowfall47 inper year; 62 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: Hysham 25 Sse, MT (8 mi away); precipitation: Hysham 25 Sse, MT (8 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.

Crow Agency, MT · 27 mi

590644b

Pompeys Pillar, MT · 28 mi

590344b

Hardin, MT · 30 mi

590314b

Garryowen, MT · 32 mi

Montana planting zones →

Questions about 59010

What planting zone is ZIP code 59010?

ZIP code 59010 (Bighorn, 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 Bighorn, MT?

The median last spring frost (32 °F) near 59010 is May 26; after June 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Hysham 25 Sse station.

When is the first frost in Bighorn, MT?

The median first fall frost near 59010 is September 16, giving a median frost-free growing season of 111 days.

When should I plant tomatoes in 59010?

Start tomato seeds indoors around Mar 31 – Apr 14 and set transplants outside around Jun 2 – Jun 16, one to three weeks after the median last frost.

How much rain and snow does 59010 get?

About 14.9 inches of precipitation a year and 47 inches of snowfall (NOAA 1991–2020 normals, Hysham 25 Sse station).

How hot do summers get in Bighorn, MT?

The average high peaks at 88 °F in July, with about 39 days a year at 90 °F or more.

What kind of soil does 59010 have?

The USDA soil survey maps Midway at the center of ZIP 59010: clay loam, well drained, pH about 7.2 (neutral).

Did spring come early in Bighorn, MT in 2026?

Spring leaf-out near 59010 came on Mar 16 in 2026, 22 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Bighorn, MT?

Long-day onions: the longest day near 59010 is 15 h 45 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59010 change?

Yes. The 2012 USDA map put 59010 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.