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

Planting zone for 59823 — Bonner, MT

ZIP code 59823 (Bonner, Missoula County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 10 and the first fall frost October 1.

Where ZIP 59823 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.

Zone5b−15 to −10 °F

Coldest night−26.1 to −23.3 °C

Last frostMay 10

First frostOct 1

2012 zone4b

Was 4b on the 2012 map — a full zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Bonner, 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 Bonner, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 10median — 50% chance of a later frost

Safe for tender plantsMay 28only 10% chance of frost after

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

Growing season143 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 28 and returns around October 12.

From the NOAA station Missoula 2 Ne, MT — 18 miles away, elevation 3,419 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 59823

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 29 – Apr 12

SpinachSow outdoors · Mar 29 – Apr 19

Broccoli, cabbageStart indoors · Mar 1 – Mar 15

Broccoli, cabbageTransplant · Apr 19 – May 3

Onion setsPlant outdoors · Apr 12 – Apr 26

PotatoesPlant outdoors · Apr 19 – May 3

LettuceSow outdoors · Apr 12 – Apr 26

Carrots, beetsSow outdoors · Apr 19 – May 3

TomatoesStart indoors · Mar 15 – Mar 29

TomatoesTransplant · May 17 – May 31

Peppers, eggplantStart indoors · Mar 1 – Mar 15

Peppers, eggplantTransplant · May 24 – Jun 7

BeansSow outdoors · May 17 – May 31

Sweet cornSow outdoors · May 17 – May 31

Cucumbers, squashSow outdoors · May 17 – May 31

Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20

GarlicPlant cloves · Sep 17 – Oct 22

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 10) and first fall frost (Oct 1) 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 59823 came on Apr 12 — 9 days earlier than the 1991–2020 average (Apr 21).

average
Apr 212026
Apr 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 5b in Montana

561 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. 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 Bonner, MT.

Soil in Bonner, MT

The soil mapped at the center of ZIP 59823 is Winkler — slightly decomposed plant material, somewhat excessively drained.

TextureSlightly decomposed plant materialtop layer

pH5.0strongly 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: Winkler very gravelly sandy loam, 30 to 60 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 59823; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Bonner, MT

Summer high82 °Faverage high, July

Winter low8 °Faverage low, January

Hot days16days a year at 90 °F or more

Freezing nights247nights a year at 32 °F or less

Growing degree days1,019base 50 °F — the season’s usable heat

Longest day15 h 53 mindaylight on June 21

Shortest day8 h 31 mindaylight on December 21

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

Precipitation15.1 inper year, rain and melted snow

Snowfall52 inper year; 102 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: Potomac, MT (7 mi away); precipitation: Potomac, MT (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Seeley Lake, MT · 18 mi

Montana planting zones →

Questions about 59823

What planting zone is ZIP code 59823?

ZIP code 59823 (Bonner, MT) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Bonner, MT?

The median last spring frost (32 °F) near 59823 is May 10; after May 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Missoula 2 Ne station.

When is the first frost in Bonner, MT?

The median first fall frost near 59823 is October 1, giving a median frost-free growing season of 143 days.

When should I plant tomatoes in 59823?

Start tomato seeds indoors around Mar 15 – Mar 29 and set transplants outside around May 17 – May 31, one to three weeks after the median last frost.

How much rain and snow does 59823 get?

About 15.1 inches of precipitation a year and 52 inches of snowfall (NOAA 1991–2020 normals, Potomac station).

How hot do summers get in Bonner, MT?

The average high peaks at 82 °F in July, with about 16 days a year at 90 °F or more.

What kind of soil does 59823 have?

The USDA soil survey maps Winkler at the center of ZIP 59823: slightly decomposed plant material, somewhat excessively drained, pH about 5.0 (strongly acidic).

Did spring come early in Bonner, MT in 2026?

Spring leaf-out near 59823 came on Apr 12 in 2026, 9 days earlier than the 1991–2020 average (Apr 21), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Bonner, MT?

Long-day onions: the longest day near 59823 is 15 h 53 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59823 change?

Yes. The 2012 USDA map put 59823 in zone 4b; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.