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

Planting zone for 59851 — Milltown, MT

ZIP code 59851 (Milltown, Missoula County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 10 and the first fall frost October 1.

Where ZIP 59851 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 10
First frostOct 1
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 Milltown, 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 Milltown, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 10median — 50% chance of a later frost
Safe for tender plantsMay 28only 10% chance of frost after
First fall frostOctober 1median — 10% chance by Sep 16
Growing season143 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 28 and returns around October 12.

From the NOAA station Missoula 2 Ne, MT — 5 miles away, elevation 3,419 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 59851

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 29 – Apr 12
SpinachSow outdoors · Mar 29 – Apr 19
Broccoli, cabbageStart indoors · Mar 1 – Mar 15
Broccoli, cabbageTransplant · Apr 19 – May 3
Onion setsPlant outdoors · Apr 12 – Apr 26
PotatoesPlant outdoors · Apr 19 – May 3
LettuceSow outdoors · Apr 12 – Apr 26
Carrots, beetsSow outdoors · Apr 19 – May 3
TomatoesStart indoors · Mar 15 – Mar 29
TomatoesTransplant · May 17 – May 31
Peppers, eggplantStart indoors · Mar 1 – Mar 15
Peppers, eggplantTransplant · May 24 – Jun 7
BeansSow outdoors · May 17 – May 31
Sweet cornSow outdoors · May 17 – May 31
Cucumbers, squashSow outdoors · May 17 – May 31
Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20
GarlicPlant cloves · Sep 17 – Oct 22
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 10) and first fall frost (Oct 1) 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 59851 came on Apr 3 — 12 days earlier than the 1991–2020 average (Apr 15).

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.

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 97

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 259

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 Milltown, MT.

Soil in Milltown, MT

The center of ZIP 59851 is mapped as Orthents, 0 to 4 percent slopes: built-over ground without natural soil data. Garden soil here is usually imported or disturbed — test before you plant.

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 59851; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Milltown, MT

Summer high85 °Faverage high, July
Winter low20 °Faverage low, January
Hot days22days a year at 90 °F or more
Freezing nights163nights a year at 32 °F or less
Growing degree days1,932base 50 °F — the season’s usable heat
Longest day15 h 53 mindaylight on June 21
Shortest day8 h 31 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation20.9 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 34 °F, low 20 °F 34°20° JanFebruary: average high 39 °F, low 22 °F 39°22° FebMarch: average high 49 °F, low 27 °F 49°27° MarApril: average high 57 °F, low 33 °F 57°33° AprMay: average high 67 °F, low 41 °F 67°41° MayJune: average high 73 °F, low 47 °F 73°47° JunJuly: average high 85 °F, low 52 °F 85°52° JulAugust: average high 84 °F, low 51 °F 84°51° AugSeptember: average high 73 °F, low 44 °F 73°44° SepOctober: average high 57 °F, low 34 °F 57°34° OctNovember: average high 41 °F, low 26 °F 41°26° NovDecember: average high 33 °F, low 20 °F 33°20° Dec

Precipitation by month inches

0″1″2″3″January: 1.72 in precipitation 1.7 JanFebruary: 1.53 in precipitation 1.5 FebMarch: 1.54 in precipitation 1.5 MarApril: 1.90 in precipitation 1.9 AprMay: 2.59 in precipitation 2.6 MayJune: 2.33 in precipitation 2.3 JunJuly: 1.07 in precipitation 1.1 JulAugust: 1.13 in precipitation 1.1 AugSeptember: 1.49 in precipitation 1.5 SepOctober: 1.89 in precipitation 1.9 OctNovember: 2.00 in precipitation 2.0 NovDecember: 1.73 in precipitation 1.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Missoula 2 Ne, MT (5 mi away); precipitation: Bonner-West Riverside 4.0 Se, 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.

598025b
Missoula, MT · 3 mi
598076a
Missoula, MT · 5 mi
598125b
Missoula, MT · 5 mi
598065b
Missoula, MT · 6 mi
598015b
Missoula, MT · 6 mi
598035b
Missoula, MT · 7 mi
598085b
Missoula, MT · 12 mi
598235b
Bonner, MT · 14 mi

Montana planting zones →

Questions about 59851

What planting zone is ZIP code 59851?

ZIP code 59851 (Milltown, 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 Milltown, MT?

The median last spring frost (32 °F) near 59851 is May 10; after May 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Missoula 2 Ne station.

When is the first frost in Milltown, MT?

The median first fall frost near 59851 is October 1, giving a median frost-free growing season of 143 days.

When should I plant tomatoes in 59851?

Start tomato seeds indoors around Mar 15 – Mar 29 and set transplants outside around May 17 – May 31, one to three weeks after the median last frost.

How much rain and snow does 59851 get?

About 20.9 inches of precipitation a year (NOAA 1991–2020 normals, Bonner-West Riverside 4.0 Se station).

How hot do summers get in Milltown, MT?

The average high peaks at 85 °F in July, with about 22 days a year at 90 °F or more.

Did spring come early in Milltown, MT in 2026?

Spring leaf-out near 59851 came on Apr 3 in 2026, 12 days earlier than the 1991–2020 average (Apr 15), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Milltown, MT?

Long-day onions: the longest day near 59851 is 15 h 53 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).