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

Planting zone for 59746 — Polaris, MT

ZIP code 59746 (Polaris, Beaverhead County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is June 5 and the first fall frost September 13.

Where ZIP 59746 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 frostJun 5

First frostSep 13

2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Polaris, 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 Polaris, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 5median — 50% chance of a later frost

Safe for tender plantsJune 23only 10% chance of frost after

First fall frostSeptember 13median — 10% chance by Aug 29

Growing season98 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 16 and returns around September 25.

From the NOAA station Dillon U Of Montana Western, MT — 24 miles away, elevation 5,128 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 59746

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 24 – May 8

SpinachSow outdoors · Apr 24 – May 15

Broccoli, cabbageStart indoors · Mar 27 – Apr 10

Broccoli, cabbageTransplant · May 15 – May 29

Onion setsPlant outdoors · May 8 – May 22

PotatoesPlant outdoors · May 15 – May 29

LettuceSow outdoors · May 8 – May 22

Carrots, beetsSow outdoors · May 15 – May 29

TomatoesStart indoors · Apr 10 – Apr 24

TomatoesTransplant · Jun 12 – Jun 26

Peppers, eggplantStart indoors · Mar 27 – Apr 10

Peppers, eggplantTransplant · Jun 19 – Jul 3

BeansSow outdoors · Jun 12 – Jun 26

Sweet cornSow outdoors · Jun 12 – Jun 26

Cucumbers, squashSow outdoors · Jun 12 – Jun 26

Fall lettuce, spinachSow outdoors · Jul 19 – Aug 2

GarlicPlant cloves · Aug 30 – Oct 4

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 5) and first fall frost (Sep 13) 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 59746 came on May 12 — 11 days earlier than the 1991–2020 average (May 23).

average
May 232026
May 12

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 Polaris, MT.

Soil in Polaris, MT

The soil mapped at the center of ZIP 59746 is Como — slightly decomposed plant material, somewhat excessively drained.

TextureSlightly decomposed plant materialtop layer

pH5.5moderately acidic; most vegetables like 6.0–7.0

DrainageSomewhat excessively drainednatural drainage class

Organic matter75%high

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Como-Comad-Garlet families, complex, moderately steep mountain 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 59746; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Polaris, MT

Summer high81 °Faverage high, July

Winter low7 °Faverage low, December

Hot days4days a year at 90 °F or more

Freezing nights230nights a year at 32 °F or less

Growing degree days1,053base 50 °F — the season’s usable heat

Longest day15 h 40 mindaylight on June 21

Shortest day8 h 43 mindaylight on December 21

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

Precipitation30.5 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: Dillon 18 Wsw, MT (16 mi away); precipitation: Mule Creek, MT (5 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.

Wise River, MT · 41 mi

Montana planting zones →

Questions about 59746

What planting zone is ZIP code 59746?

ZIP code 59746 (Polaris, 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 Polaris, MT?

The median last spring frost (32 °F) near 59746 is June 5; after June 23 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Dillon U Of Montana Western station.

When is the first frost in Polaris, MT?

The median first fall frost near 59746 is September 13, giving a median frost-free growing season of 98 days.

When should I plant tomatoes in 59746?

Start tomato seeds indoors around Apr 10 – Apr 24 and set transplants outside around Jun 12 – Jun 26, one to three weeks after the median last frost.

How much rain and snow does 59746 get?

About 30.5 inches of precipitation a year (NOAA 1991–2020 normals, Mule Creek station).

How hot do summers get in Polaris, MT?

The average high peaks at 81 °F in July, with about 4 days a year at 90 °F or more.

What kind of soil does 59746 have?

The USDA soil survey maps Como at the center of ZIP 59746: slightly decomposed plant material, somewhat excessively drained, pH about 5.5 (moderately acidic).

Did spring come early in Polaris, MT in 2026?

Spring leaf-out near 59746 came on May 12 in 2026, 11 days earlier than the 1991–2020 average (May 23), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Polaris, MT?

Long-day onions: the longest day near 59746 is 15 h 40 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59746 change?

Yes. The 2012 USDA map put 59746 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.