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

Planting zone for 59829 — Darby, MT

ZIP code 59829 (Darby, Ravalli County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is June 1 and the first fall frost September 17.

Where ZIP 59829 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 frostJun 1

First frostSep 17

2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Darby, 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 Darby, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 1median — 50% chance of a later frost

Safe for tender plantsJune 19only 10% chance of frost after

First fall frostSeptember 17median — 10% chance by Sep 2

Growing season107 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 10 and returns around September 30.

From the NOAA station Gibbonsville #2, ID — 19 miles away, elevation 4,482 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 59829

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 20 – May 4

SpinachSow outdoors · Apr 20 – May 11

Broccoli, cabbageStart indoors · Mar 23 – Apr 6

Broccoli, cabbageTransplant · May 11 – May 25

Onion setsPlant outdoors · May 4 – May 18

PotatoesPlant outdoors · May 11 – May 25

LettuceSow outdoors · May 4 – May 18

Carrots, beetsSow outdoors · May 11 – May 25

TomatoesStart indoors · Apr 6 – Apr 20

TomatoesTransplant · Jun 8 – Jun 22

Peppers, eggplantStart indoors · Mar 23 – Apr 6

Peppers, eggplantTransplant · Jun 15 – Jun 29

BeansSow outdoors · Jun 8 – Jun 22

Sweet cornSow outdoors · Jun 8 – Jun 22

Cucumbers, squashSow outdoors · Jun 8 – Jun 22

Fall lettuce, spinachSow outdoors · Jul 23 – Aug 6

GarlicPlant cloves · Sep 3 – Oct 8

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 1) and first fall frost (Sep 17) 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 59829 came on May 3 — 11 days earlier than the 1991–2020 average (May 14).

average
May 142026
May 3

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 Darby, MT.

Soil in Darby, MT

The soil mapped at the center of ZIP 59829 is Priestlake family — moderately decomposed plant material, excessively drained.

TextureModerately decomposed plant materialtop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageExcessively drainednatural drainage class

Organic matter70%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Priestlake family-Rubycreek family, complex, trough walls, extremely bouldery.

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 59829; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Darby, MT

Summer high82 °Faverage high, July

Winter low12 °Faverage low, December

Hot days10days a year at 90 °F or more

Freezing nights230nights a year at 32 °F or less

Growing degree days1,144base 50 °F — the season’s usable heat

Longest day15 h 43 mindaylight on June 21

Shortest day8 h 40 mindaylight on December 21

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

Precipitation35.5 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: Sula 3 Ene, MT (14 mi away); precipitation: Saddle Mtn., MT (11 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

598275b

Conner, MT · 11 mi

834635b

Gibbonsville, ID · 16 mi

598715a

Sula, MT · 20 mi

834666a

North Fork, ID · 24 mi

598405b

Hamilton, MT · 29 mi

598355b

Grantsdale, MT · 31 mi

Montana planting zones →

Questions about 59829

What planting zone is ZIP code 59829?

ZIP code 59829 (Darby, 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 Darby, MT?

The median last spring frost (32 °F) near 59829 is June 1; after June 19 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Gibbonsville #2 station.

When is the first frost in Darby, MT?

The median first fall frost near 59829 is September 17, giving a median frost-free growing season of 107 days.

When should I plant tomatoes in 59829?

Start tomato seeds indoors around Apr 6 – Apr 20 and set transplants outside around Jun 8 – Jun 22, one to three weeks after the median last frost.

How much rain and snow does 59829 get?

About 35.5 inches of precipitation a year (NOAA 1991–2020 normals, Saddle Mtn. station).

How hot do summers get in Darby, MT?

The average high peaks at 82 °F in July, with about 10 days a year at 90 °F or more.

What kind of soil does 59829 have?

The USDA soil survey maps Priestlake family at the center of ZIP 59829: moderately decomposed plant material, excessively drained, pH about 5.0 (strongly acidic).

Did spring come early in Darby, MT in 2026?

Spring leaf-out near 59829 came on May 3 in 2026, 11 days earlier than the 1991–2020 average (May 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Darby, MT?

Long-day onions: the longest day near 59829 is 15 h 43 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59829 change?

Yes. The 2012 USDA map put 59829 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.