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

Planting zone for 59859 — Plains, MT

ZIP code 59859 (Plains, Sanders County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 17 and the first fall frost September 23.

Where ZIP 59859 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.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 17
First frostSep 23
2012 zone6a

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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Plains, 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 Plains, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 17median — 50% chance of a later frost
Safe for tender plantsJune 8only 10% chance of frost after
First fall frostSeptember 23median — 10% chance by Sep 6
Growing season125 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 1 and returns around October 6.

From the NOAA station Superior, MT — 23 miles away, elevation 2,710 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 59859

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 5 – Apr 19
SpinachSow outdoors · Apr 5 – Apr 26
Broccoli, cabbageStart indoors · Mar 8 – Mar 22
Broccoli, cabbageTransplant · Apr 26 – May 10
Onion setsPlant outdoors · Apr 19 – May 3
PotatoesPlant outdoors · Apr 26 – May 10
LettuceSow outdoors · Apr 19 – May 3
Carrots, beetsSow outdoors · Apr 26 – May 10
TomatoesStart indoors · Mar 22 – Apr 5
TomatoesTransplant · May 24 – Jun 7
Peppers, eggplantStart indoors · Mar 8 – Mar 22
Peppers, eggplantTransplant · May 31 – Jun 14
BeansSow outdoors · May 24 – Jun 7
Sweet cornSow outdoors · May 24 – Jun 7
Cucumbers, squashSow outdoors · May 24 – Jun 7
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 17) 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 59859 came on Apr 12 — 15 days earlier than the 1991–2020 average (Apr 27).

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 6a in Montana

572 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 28

American elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °FDouglas-fir200 ft · blooms mid spring · medium shade tolerance · to −33 °Feastern cottonwood190 ft · blooms spring · high shade tolerance · to −43 °F

Shrubs 100

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °Falderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °F

Wildflowers & perennials 266

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °F

Grasses 164

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 3

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

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 Plains, MT.

Soil in Plains, MT

The soil mapped at the center of ZIP 59859 is Doglake — extremely cobbly loam, excessively drained.

TextureExtremely cobbly loama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageExcessively drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Doglake extremely cobbly loam, 2 to 12 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 59859; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Plains, MT

Summer high87 °Faverage high, August
Winter low21 °Faverage low, February
Hot days29days a year at 90 °F or more
Freezing nights191nights a year at 32 °F or less
Growing degree days1,792base 50 °F — the season’s usable heat
Longest day15 h 58 mindaylight on June 21
Shortest day8 h 26 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation16.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 35 °F, low 22 °F 35°22° JanFebruary: average high 41 °F, low 21 °F 41°21° FebMarch: average high 51 °F, low 26 °F 51°26° MarApril: average high 59 °F, low 32 °F 59°32° AprMay: average high 69 °F, low 38 °F 69°38° MayJune: average high 77 °F, low 44 °F 77°44° JunJuly: average high 86 °F, low 47 °F 86°47° JulAugust: average high 87 °F, low 45 °F 87°45° AugSeptember: average high 76 °F, low 39 °F 76°39° SepOctober: average high 59 °F, low 32 °F 59°32° OctNovember: average high 42 °F, low 26 °F 42°26° NovDecember: average high 33 °F, low 21 °F 33°21° Dec

Precipitation by month inches

0″1″2″3″January: 1.19 in precipitation 1.2 JanFebruary: 1.29 in precipitation 1.3 FebMarch: 1.11 in precipitation 1.1 MarApril: 1.36 in precipitation 1.4 AprMay: 1.80 in precipitation 1.8 MayJune: 2.03 in precipitation 2.0 JunJuly: 0.93 in precipitation 0.9 JulAugust: 1.05 in precipitation 1.1 AugSeptember: 0.99 in precipitation 1.0 SepOctober: 1.34 in precipitation 1.3 OctNovember: 1.95 in precipitation 1.9 NovDecember: 1.38 in precipitation 1.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Saint Regis 1 Ne, MT (20 mi away); precipitation: Superior, MT (23 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.

598566a
Paradise, MT · 10 mi
598486a
Lonepine, MT · 14 mi
598456a
Hot Springs, MT · 16 mi
598666a
Saint Regis, MT · 20 mi
598736a
Thompson Falls, MT · 24 mi
598316a
Dixon, MT · 27 mi
599156a
Elmo, MT · 27 mi
598465b
Huson, MT · 29 mi

Montana planting zones →

Questions about 59859

What planting zone is ZIP code 59859?

ZIP code 59859 (Plains, MT) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Plains, MT?

The median last spring frost (32 °F) near 59859 is May 17; after June 8 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Superior station.

When is the first frost in Plains, MT?

The median first fall frost near 59859 is September 23, giving a median frost-free growing season of 125 days.

When should I plant tomatoes in 59859?

Start tomato seeds indoors around Mar 22 – Apr 5 and set transplants outside around May 24 – Jun 7, one to three weeks after the median last frost.

How much rain and snow does 59859 get?

About 16.4 inches of precipitation a year (NOAA 1991–2020 normals, Superior station).

How hot do summers get in Plains, MT?

The average high peaks at 87 °F in August, with about 29 days a year at 90 °F or more.

What kind of soil does 59859 have?

The USDA soil survey maps Doglake at the center of ZIP 59859: extremely cobbly loam, excessively drained, pH about 6.7 (neutral).

Did spring come early in Plains, MT in 2026?

Spring leaf-out near 59859 came on Apr 12 in 2026, 15 days earlier than the 1991–2020 average (Apr 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Plains, MT?

Long-day onions: the longest day near 59859 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).