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

Planting zone for 59828 — Corvallis, MT

ZIP code 59828 (Corvallis, Ravalli County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 23 and the first fall frost September 21.

Where ZIP 59828 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 23

First frostSep 21

2012 zone5b

Same zone as on the 2012 map. 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 Corvallis, 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 Corvallis, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 23median — 50% chance of a later frost

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

First fall frostSeptember 21median — 10% chance by Sep 5

Growing season118 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 5 and returns around October 2.

From the NOAA station Western Ag Rsch Center, MT — 6 miles away, elevation 3,609 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 59828

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 11 – Apr 25

SpinachSow outdoors · Apr 11 – May 2

Broccoli, cabbageStart indoors · Mar 14 – Mar 28

Broccoli, cabbageTransplant · May 2 – May 16

Onion setsPlant outdoors · Apr 25 – May 9

PotatoesPlant outdoors · May 2 – May 16

LettuceSow outdoors · Apr 25 – May 9

Carrots, beetsSow outdoors · May 2 – May 16

TomatoesStart indoors · Mar 28 – Apr 11

TomatoesTransplant · May 30 – Jun 13

Peppers, eggplantStart indoors · Mar 14 – Mar 28

Peppers, eggplantTransplant · Jun 6 – Jun 20

BeansSow outdoors · May 30 – Jun 13

Sweet cornSow outdoors · May 30 – Jun 13

Cucumbers, squashSow outdoors · May 30 – Jun 13

Fall lettuce, spinachSow outdoors · Jul 27 – Aug 10

GarlicPlant cloves · Sep 7 – Oct 12

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 23) and first fall frost (Sep 21) 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 59828 came on Apr 7 — 28 days earlier than the 1991–2020 average (May 5).

average
May 52026
Apr 7

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 Corvallis, MT.

Soil in Corvallis, MT

The soil mapped at the center of ZIP 59828 is Holter — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables

pH7.2neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Holter-Tolman families, complex, dissected 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 59828; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Corvallis, MT

Summer high86 °Faverage high, July

Winter low18 °Faverage low, December

Hot days23days a year at 90 °F or more

Freezing nights165nights a year at 32 °F or less

Growing degree days1,789base 50 °F — the season’s usable heat

Longest day15 h 48 mindaylight on June 21

Shortest day8 h 36 mindaylight on December 21

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

Precipitation15.8 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: Western Ag Rsch Center, MT (6 mi away); precipitation: Corvallis 4.2 Ene, MT (3 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.

598355b

Grantsdale, MT · 12 mi

598415b

Pinesdale, MT · 13 mi

598405b

Hamilton, MT · 13 mi

598705b

Stevensville, MT · 14 mi

Philipsburg, MT · 24 mi

598255b

Clinton, MT · 25 mi

Montana planting zones →

Questions about 59828

What planting zone is ZIP code 59828?

ZIP code 59828 (Corvallis, 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 Corvallis, MT?

The median last spring frost (32 °F) near 59828 is May 23; after June 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Western Ag Rsch Center station.

When is the first frost in Corvallis, MT?

The median first fall frost near 59828 is September 21, giving a median frost-free growing season of 118 days.

When should I plant tomatoes in 59828?

Start tomato seeds indoors around Mar 28 – Apr 11 and set transplants outside around May 30 – Jun 13, one to three weeks after the median last frost.

How much rain and snow does 59828 get?

About 15.8 inches of precipitation a year (NOAA 1991–2020 normals, Corvallis 4.2 Ene station).

How hot do summers get in Corvallis, MT?

The average high peaks at 86 °F in July, with about 23 days a year at 90 °F or more.

What kind of soil does 59828 have?

The USDA soil survey maps Holter at the center of ZIP 59828: gravelly loam, well drained, pH about 7.2 (neutral).

Did spring come early in Corvallis, MT in 2026?

Spring leaf-out near 59828 came on Apr 7 in 2026, 28 days earlier than the 1991–2020 average (May 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Corvallis, MT?

Long-day onions: the longest day near 59828 is 15 h 48 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).