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

Planting zone for 59003 — Ashland, MT

ZIP code 59003 (Ashland, Rosebud County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 25 and the first fall frost September 19.

Where ZIP 59003 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 25

First frostSep 19

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 Ashland, 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 Ashland, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 25median — 50% chance of a later frost

Safe for tender plantsJune 7only 10% chance of frost after

First fall frostSeptember 19median — 10% chance by Sep 1

Growing season115 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 14 and returns around September 29.

From the NOAA station Sonnette 7 Sw, MT — 18 miles away, elevation 3,914 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 59003

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 13 – Apr 27

SpinachSow outdoors · Apr 13 – May 4

Broccoli, cabbageStart indoors · Mar 16 – Mar 30

Broccoli, cabbageTransplant · May 4 – May 18

Onion setsPlant outdoors · Apr 27 – May 11

PotatoesPlant outdoors · May 4 – May 18

LettuceSow outdoors · Apr 27 – May 11

Carrots, beetsSow outdoors · May 4 – May 18

TomatoesStart indoors · Mar 30 – Apr 13

TomatoesTransplant · Jun 1 – Jun 15

Peppers, eggplantStart indoors · Mar 16 – Mar 30

Peppers, eggplantTransplant · Jun 8 – Jun 22

BeansSow outdoors · Jun 1 – Jun 15

Sweet cornSow outdoors · Jun 1 – Jun 15

Cucumbers, squashSow outdoors · Jun 1 – Jun 15

Fall lettuce, spinachSow outdoors · Jul 25 – Aug 8

GarlicPlant cloves · Sep 5 – Oct 10

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 25) and first fall frost (Sep 19) 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 59003 came on Mar 23 — 15 days earlier than the 1991–2020 average (Apr 7).

average
Apr 72026
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 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 Ashland, MT.

Soil in Ashland, MT

The soil mapped at the center of ZIP 59003 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 and Bainville rocky soils, 35 to 75 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 59003; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ashland, MT

Summer high87 °Faverage high, July

Winter low10 °Faverage low, January

Hot days24days a year at 90 °F or more

Freezing nights199nights a year at 32 °F or less

Growing degree days2,068base 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)

Precipitation17 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: Sonnette 7 Sw, MT (18 mi away); precipitation: Ashland 11.9 E, MT (11 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.

590044b

Ashland, MT · 8 mi

590435a

Lame Deer, MT · 23 mi

All 2 ZIP codes in Ashland → · Montana planting zones →

Questions about 59003

What planting zone is ZIP code 59003?

ZIP code 59003 (Ashland, 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 Ashland, MT?

The median last spring frost (32 °F) near 59003 is May 25; after June 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sonnette 7 Sw station.

When is the first frost in Ashland, MT?

The median first fall frost near 59003 is September 19, giving a median frost-free growing season of 115 days.

When should I plant tomatoes in 59003?

Start tomato seeds indoors around Mar 30 – Apr 13 and set transplants outside around Jun 1 – Jun 15, one to three weeks after the median last frost.

How much rain and snow does 59003 get?

About 17 inches of precipitation a year (NOAA 1991–2020 normals, Ashland 11.9 E station).

How hot do summers get in Ashland, MT?

The average high peaks at 87 °F in July, with about 24 days a year at 90 °F or more.

What kind of soil does 59003 have?

The USDA soil survey maps Midway at the center of ZIP 59003: clay loam, well drained, pH about 7.2 (neutral).

Did spring come early in Ashland, MT in 2026?

Spring leaf-out near 59003 came on Mar 23 in 2026, 15 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ashland, MT?

Long-day onions: the longest day near 59003 is 15 h 41 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59003 change?

Yes. The 2012 USDA map put 59003 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.