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

Planting zone for 59523 — Chinook, MT

ZIP code 59523 (Chinook, Blaine County) is in USDA zone 3b: the coldest winter night averages −35 to −30 °F. The median last spring frost is May 14 and the first fall frost September 23.

Where ZIP 59523 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.

Zone3b−35 to −30 °F

Coldest night−37.2 to −34.4 °C

Last frostMay 14

First frostSep 23

2012 zone3b

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 3b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Chinook, 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 Chinook, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 14median — 50% chance of a later frost

Safe for tender plantsMay 27only 10% chance of frost after

First fall frostSeptember 23median — 10% chance by Sep 11

Growing season130 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around October 1.

From the NOAA station Chinook, MT — 4 miles away, elevation 2,421 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 59523

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 2 – Apr 16

SpinachSow outdoors · Apr 2 – Apr 23

Broccoli, cabbageStart indoors · Mar 5 – Mar 19

Broccoli, cabbageTransplant · Apr 23 – May 7

Onion setsPlant outdoors · Apr 16 – Apr 30

PotatoesPlant outdoors · Apr 23 – May 7

LettuceSow outdoors · Apr 16 – Apr 30

Carrots, beetsSow outdoors · Apr 23 – May 7

TomatoesStart indoors · Mar 19 – Apr 2

TomatoesTransplant · May 21 – Jun 4

Peppers, eggplantStart indoors · Mar 5 – Mar 19

Peppers, eggplantTransplant · May 28 – Jun 11

BeansSow outdoors · May 21 – Jun 4

Sweet cornSow outdoors · May 21 – Jun 4

Cucumbers, squashSow outdoors · May 21 – Jun 4

Fall lettuce, spinachSow outdoors · Jul 29 – Aug 12

GarlicPlant cloves · Sep 9 – Oct 14

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 14) and first fall frost (Sep 23) 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 59523 came on Mar 23 — 22 days earlier than the 1991–2020 average (Apr 14).

average
Apr 142026
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).

Soil in Chinook, MT

The soil mapped at the center of ZIP 59523 is Zahill — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up

pH8.0alkaline; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.5%low — add compost

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Zahill-Vida clay loams, 8 to 25 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 59523; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Chinook, MT

Summer high84 °Faverage high, July

Winter low4 °Faverage low, January

Hot days24days a year at 90 °F or more

Freezing nights195nights a year at 32 °F or less

Growing degree days1,979base 50 °F — the season’s usable heat

Longest day16 h 08 mindaylight on June 21

Shortest day8 h 18 mindaylight on December 21

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

Precipitation13.4 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: Chinook, MT (4 mi away); precipitation: Chinook, MT (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Box Elder, MT · 38 mi

Montana planting zones →

Questions about 59523

What planting zone is ZIP code 59523?

ZIP code 59523 (Chinook, MT) is in USDA hardiness zone 3b on the 2023 map: the coldest night of an average winter reaches −35 to −30 °F (−37.2 to −34.4 °C).

When is the last frost in Chinook, MT?

The median last spring frost (32 °F) near 59523 is May 14; after May 27 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Chinook station.

When is the first frost in Chinook, MT?

The median first fall frost near 59523 is September 23, giving a median frost-free growing season of 130 days.

When should I plant tomatoes in 59523?

Start tomato seeds indoors around Mar 19 – Apr 2 and set transplants outside around May 21 – Jun 4, one to three weeks after the median last frost.

How much rain and snow does 59523 get?

About 13.4 inches of precipitation a year (NOAA 1991–2020 normals, Chinook station).

How hot do summers get in Chinook, MT?

The average high peaks at 84 °F in July, with about 24 days a year at 90 °F or more.

What kind of soil does 59523 have?

The USDA soil survey maps Zahill at the center of ZIP 59523: clay loam, well drained, pH about 8.0 (alkaline).

Did spring come early in Chinook, MT in 2026?

Spring leaf-out near 59523 came on Mar 23 in 2026, 22 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Chinook, MT?

Long-day onions: the longest day near 59523 is 16 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).