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

Planting zone for 59058 — Mosby, MT

ZIP code 59058 (Mosby, Garfield County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 5 and the first fall frost October 4.

Where ZIP 59058 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 frostMay 5
First frostOct 4
2012 zone4a

Was 4a on the 2012 map — half a zone warmer now. 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 Mosby, 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 Mosby, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 5median — 50% chance of a later frost
Safe for tender plantsMay 26only 10% chance of frost after
First fall frostOctober 4median — 10% chance by Sep 22
Growing season151 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 14.

From the NOAA station Mosby 4 Ene, MT — 4 miles away, elevation 2,910 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 59058

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 24 – Apr 7
SpinachSow outdoors · Mar 24 – Apr 14
Broccoli, cabbageStart indoors · Feb 24 – Mar 10
Broccoli, cabbageTransplant · Apr 14 – Apr 28
Onion setsPlant outdoors · Apr 7 – Apr 21
PotatoesPlant outdoors · Apr 14 – Apr 28
LettuceSow outdoors · Apr 7 – Apr 21
Carrots, beetsSow outdoors · Apr 14 – Apr 28
TomatoesStart indoors · Mar 10 – Mar 24
TomatoesTransplant · May 12 – May 26
Peppers, eggplantStart indoors · Feb 24 – Mar 10
Peppers, eggplantTransplant · May 19 – Jun 2
BeansSow outdoors · May 12 – May 26
Sweet cornSow outdoors · May 12 – May 26
Cucumbers, squashSow outdoors · May 12 – May 26
Fall lettuce, spinachSow outdoors · Aug 9 – Aug 23
GarlicPlant cloves · Sep 20 – Oct 25
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 5) and first fall frost (Oct 4) 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 59058 came on Mar 23 — 15 days earlier than the 1991–2020 average (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 4b in Montana

506 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 23

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 87

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 229

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 155

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 Mosby, MT.

Soil in Mosby, MT

The soil mapped at the center of ZIP 59058 is Neldore — silty clay loam, well drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Neldore-Abor silty clays, 2 to 15 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 59058; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mosby, MT

Summer high88 °Faverage high, July
Winter low14 °Faverage low, January
Hot days35days a year at 90 °F or more
Freezing nights159nights a year at 32 °F or less
Growing degree days2,704base 50 °F — the season’s usable heat
Longest day15 h 54 mindaylight on June 21
Shortest day8 h 30 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation14.5 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 34 °F, low 14 °F 34°14° JanFebruary: average high 38 °F, low 17 °F 38°17° FebMarch: average high 49 °F, low 26 °F 49°26° MarApril: average high 59 °F, low 35 °F 59°35° AprMay: average high 68 °F, low 44 °F 68°44° MayJune: average high 78 °F, low 53 °F 78°53° JunJuly: average high 88 °F, low 60 °F 88°60° JulAugust: average high 87 °F, low 58 °F 87°58° AugSeptember: average high 76 °F, low 48 °F 76°48° SepOctober: average high 60 °F, low 37 °F 60°37° OctNovember: average high 46 °F, low 25 °F 46°25° NovDecember: average high 37 °F, low 17 °F 37°17° Dec

Precipitation by month inches

0″1″2″3″January: 0.43 in precipitation 0.4 JanFebruary: 0.39 in precipitation 0.4 FebMarch: 0.56 in precipitation 0.6 MarApril: 1.33 in precipitation 1.3 AprMay: 2.63 in precipitation 2.6 MayJune: 2.85 in precipitation 2.9 JunJuly: 1.87 in precipitation 1.9 JulAugust: 1.18 in precipitation 1.2 AugSeptember: 1.23 in precipitation 1.2 SepOctober: 1.17 in precipitation 1.2 OctNovember: 0.47 in precipitation 0.5 NovDecember: 0.39 in precipitation 0.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Mosby 4 Ene, MT (4 mi away); precipitation: Mosby 4 Ene, MT (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 4b.

590774b
Sand Springs, MT · 19 mi
590544b
Melstone, MT · 22 mi
590874b
Winnett, MT · 24 mi
590394b
Ingomar, MT · 30 mi
590834b
Sumatra, MT · 31 mi
590594b
Musselshell, MT · 36 mi
593184b
Brusett, MT · 37 mi
590844b
Teigen, MT · 40 mi

Montana planting zones →

Questions about 59058

What planting zone is ZIP code 59058?

ZIP code 59058 (Mosby, 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 Mosby, MT?

The median last spring frost (32 °F) near 59058 is May 5; after May 26 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mosby 4 Ene station.

When is the first frost in Mosby, MT?

The median first fall frost near 59058 is October 4, giving a median frost-free growing season of 151 days.

When should I plant tomatoes in 59058?

Start tomato seeds indoors around Mar 10 – Mar 24 and set transplants outside around May 12 – May 26, one to three weeks after the median last frost.

How much rain and snow does 59058 get?

About 14.5 inches of precipitation a year (NOAA 1991–2020 normals, Mosby 4 Ene station).

How hot do summers get in Mosby, MT?

The average high peaks at 88 °F in July, with about 35 days a year at 90 °F or more.

What kind of soil does 59058 have?

The USDA soil survey maps Neldore at the center of ZIP 59058: silty clay loam, well drained, pH about 6.7 (neutral).

Did spring come early in Mosby, MT in 2026?

Spring leaf-out near 59058 came on Mar 23 in 2026, 15 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mosby, MT?

Long-day onions: the longest day near 59058 is 15 h 54 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59058 change?

Yes. The 2012 USDA map put 59058 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.