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

Planting zone for 59640 — Marysville, MT

ZIP code 59640 (Marysville, Lewis and Clark County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is June 4 and the first fall frost September 14.

Where ZIP 59640 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.

Zone4b−25 to −20 °F

Coldest night−31.7 to −28.9 °C

Last frostJun 4

First frostSep 14

2012 zone4b

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 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Marysville, 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 Marysville, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 4median — 50% chance of a later frost

Safe for tender plantsJune 18only 10% chance of frost after

First fall frostSeptember 14median — 10% chance by Aug 30

Growing season100 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 14 and returns around September 26.

From the NOAA station Austin 1 W, MT — 10 miles away, elevation 4,853 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 59640

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 23 – May 7

SpinachSow outdoors · Apr 23 – May 14

Broccoli, cabbageStart indoors · Mar 26 – Apr 9

Broccoli, cabbageTransplant · May 14 – May 28

Onion setsPlant outdoors · May 7 – May 21

PotatoesPlant outdoors · May 14 – May 28

LettuceSow outdoors · May 7 – May 21

Carrots, beetsSow outdoors · May 14 – May 28

TomatoesStart indoors · Apr 9 – Apr 23

TomatoesTransplant · Jun 11 – Jun 25

Peppers, eggplantStart indoors · Mar 26 – Apr 9

Peppers, eggplantTransplant · Jun 18 – Jul 2

BeansSow outdoors · Jun 11 – Jun 25

Sweet cornSow outdoors · Jun 11 – Jun 25

Cucumbers, squashSow outdoors · Jun 11 – Jun 25

Fall lettuce, spinachSow outdoors · Jul 20 – Aug 3

GarlicPlant cloves · Aug 31 – Oct 5

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 4) and first fall frost (Sep 14) 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 59640 came on Apr 19 — 14 days earlier than the 1991–2020 average (May 3).

average
May 32026
Apr 19

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 Marysville, MT

The soil mapped at the center of ZIP 59640 is Helmville — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH6.5neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter50%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Helmville channery loam, warm, 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 59640; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Marysville, MT

Summer high78 °Faverage high, July

Winter low13 °Faverage low, January

Hot days4days a year at 90 °F or more

Freezing nights204nights a year at 32 °F or less

Growing degree days1,244base 50 °F — the season’s usable heat

Longest day15 h 52 mindaylight on June 21

Shortest day8 h 32 mindaylight on December 21

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

Precipitation28.6 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: Austin 1 W, MT (10 mi away); precipitation: Nevada Ridge, MT (8 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.

596334b

Canyon Creek, MT · 4 mi

597134b

Avon, MT · 14 mi

596364b

Fort Harrison, MT · 16 mi

Montana planting zones →

Questions about 59640

What planting zone is ZIP code 59640?

ZIP code 59640 (Marysville, MT) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Marysville, MT?

The median last spring frost (32 °F) near 59640 is June 4; after June 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Austin 1 W station.

When is the first frost in Marysville, MT?

The median first fall frost near 59640 is September 14, giving a median frost-free growing season of 100 days.

When should I plant tomatoes in 59640?

Start tomato seeds indoors around Apr 9 – Apr 23 and set transplants outside around Jun 11 – Jun 25, one to three weeks after the median last frost.

How much rain and snow does 59640 get?

About 28.6 inches of precipitation a year (NOAA 1991–2020 normals, Nevada Ridge station).

How hot do summers get in Marysville, MT?

The average high peaks at 78 °F in July, with about 4 days a year at 90 °F or more.

What kind of soil does 59640 have?

The USDA soil survey maps Helmville at the center of ZIP 59640: slightly decomposed plant material, well drained, pH about 6.5 (neutral).

Did spring come early in Marysville, MT in 2026?

Spring leaf-out near 59640 came on Apr 19 in 2026, 14 days earlier than the 1991–2020 average (May 3), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Marysville, MT?

Long-day onions: the longest day near 59640 is 15 h 52 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).