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

Planting zone for 59336 — Ismay, MT

ZIP code 59336 (Ismay, Custer County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 22 and the first fall frost September 15.

Where ZIP 59336 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.

Zone4a−30 to −25 °F

Coldest night−34.4 to −31.7 °C

Last frostMay 22

First frostSep 15

2012 zone4b

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

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Ismay, 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 Ismay, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 22median — 50% chance of a later frost

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

First fall frostSeptember 15median — 10% chance by Sep 2

Growing season117 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around September 25.

From the NOAA station Mizpah 4 Nnw, MT — 17 miles away, elevation 2,480 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 59336

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 10 – Apr 24

SpinachSow outdoors · Apr 10 – May 1

Broccoli, cabbageStart indoors · Mar 13 – Mar 27

Broccoli, cabbageTransplant · May 1 – May 15

Onion setsPlant outdoors · Apr 24 – May 8

PotatoesPlant outdoors · May 1 – May 15

LettuceSow outdoors · Apr 24 – May 8

Carrots, beetsSow outdoors · May 1 – May 15

TomatoesStart indoors · Mar 27 – Apr 10

TomatoesTransplant · May 29 – Jun 12

Peppers, eggplantStart indoors · Mar 13 – Mar 27

Peppers, eggplantTransplant · Jun 5 – Jun 19

BeansSow outdoors · May 29 – Jun 12

Sweet cornSow outdoors · May 29 – Jun 12

Cucumbers, squashSow outdoors · May 29 – Jun 12

Fall lettuce, spinachSow outdoors · Jul 21 – Aug 4

GarlicPlant cloves · Sep 1 – Oct 6

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 22) and first fall frost (Sep 15) 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 59336 came on Mar 23 — 20 days earlier than the 1991–2020 average (Apr 12).

average
Apr 122026
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 4a in Montana

439 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −30 °F or colder — the bottom of zone 4a. 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 Ismay, MT.

Soil in Ismay, MT

The soil mapped at the center of ZIP 59336 is Cambeth — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH7.9alkaline; 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: Cambeth, calcareous-Cabbart-Kirby complex, 8 to 45 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 59336; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ismay, MT

Summer high91 °Faverage high, July

Winter low6 °Faverage low, January

Hot days47days a year at 90 °F or more

Freezing nights191nights a year at 32 °F or less

Growing degree days2,567base 50 °F — the season’s usable heat

Longest day15 h 48 mindaylight on June 21

Shortest day8 h 35 mindaylight on December 21

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

Precipitation14.5 inper year, rain and melted snow

Snowfall30 inper year; 64 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: Mizpah 4 Nnw, MT (17 mi away); precipitation: Mizpah 4 Nnw, MT (17 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.

Powderville, MT · 36 mi

Montana planting zones →

Questions about 59336

What planting zone is ZIP code 59336?

ZIP code 59336 (Ismay, MT) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Ismay, MT?

The median last spring frost (32 °F) near 59336 is May 22; after June 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mizpah 4 Nnw station.

When is the first frost in Ismay, MT?

The median first fall frost near 59336 is September 15, giving a median frost-free growing season of 117 days.

When should I plant tomatoes in 59336?

Start tomato seeds indoors around Mar 27 – Apr 10 and set transplants outside around May 29 – Jun 12, one to three weeks after the median last frost.

How much rain and snow does 59336 get?

About 14.5 inches of precipitation a year and 30 inches of snowfall (NOAA 1991–2020 normals, Mizpah 4 Nnw station).

How hot do summers get in Ismay, MT?

The average high peaks at 91 °F in July, with about 47 days a year at 90 °F or more.

What kind of soil does 59336 have?

The USDA soil survey maps Cambeth at the center of ZIP 59336: silt loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Ismay, MT in 2026?

Spring leaf-out near 59336 came on Mar 23 in 2026, 20 days earlier than the 1991–2020 average (Apr 12), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ismay, MT?

Long-day onions: the longest day near 59336 is 15 h 48 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59336 change?

Yes. The 2012 USDA map put 59336 in zone 4b; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.