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

Planting zone for 59546 — Zortman, MT

ZIP code 59546 (Zortman, Phillips County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 18 and the first fall frost September 23.

Where ZIP 59546 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 18
First frostSep 23
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 Zortman, 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 Zortman, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 18median — 50% chance of a later frost
Safe for tender plantsJune 1only 10% chance of frost after
First fall frostSeptember 23median — 10% chance by Sep 7
Growing season126 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 5 and returns around October 2.

From the NOAA station Zortman, MT — within 1 mile, elevation 4,036 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 59546

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 6 – Apr 20
SpinachSow outdoors · Apr 6 – Apr 27
Broccoli, cabbageStart indoors · Mar 9 – Mar 23
Broccoli, cabbageTransplant · Apr 27 – May 11
Onion setsPlant outdoors · Apr 20 – May 4
PotatoesPlant outdoors · Apr 27 – May 11
LettuceSow outdoors · Apr 20 – May 4
Carrots, beetsSow outdoors · Apr 27 – May 11
TomatoesStart indoors · Mar 23 – Apr 6
TomatoesTransplant · May 25 – Jun 8
Peppers, eggplantStart indoors · Mar 9 – Mar 23
Peppers, eggplantTransplant · Jun 1 – Jun 15
BeansSow outdoors · May 25 – Jun 8
Sweet cornSow outdoors · May 25 – Jun 8
Cucumbers, squashSow outdoors · May 25 – Jun 8
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 18) 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 59546 came on Mar 21 — 25 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 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 Zortman, MT.

Soil in Zortman, MT

The soil mapped at the center of ZIP 59546 is Warneke — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Warneke-Whitecow-Rock outcrop complex, 25 to 70 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 59546; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Zortman, MT

Summer high79 °Faverage high, July
Winter low14 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights186nights a year at 32 °F or less
Growing degree days1,675base 50 °F — the season’s usable heat
Longest day16 h 02 mindaylight on June 21
Shortest day8 h 23 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation19.5 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 34 °F, low 14 °F 34°14° JanFebruary: average high 34 °F, low 15 °F 34°15° FebMarch: average high 43 °F, low 22 °F 43°22° MarApril: average high 51 °F, low 30 °F 51°30° AprMay: average high 61 °F, low 39 °F 61°39° MayJune: average high 69 °F, low 47 °F 69°47° JunJuly: average high 79 °F, low 54 °F 79°54° JulAugust: average high 79 °F, low 52 °F 79°52° AugSeptember: average high 68 °F, low 43 °F 68°43° SepOctober: average high 54 °F, low 33 °F 54°33° OctNovember: average high 42 °F, low 24 °F 42°24° NovDecember: average high 35 °F, low 16 °F 35°16° Dec

Precipitation by month inches

0″1″2″3″4″January: 0.92 in precipitation 0.9 JanFebruary: 0.63 in precipitation 0.6 FebMarch: 0.83 in precipitation 0.8 MarApril: 1.77 in precipitation 1.8 AprMay: 3.18 in precipitation 3.2 MayJune: 4.00 in precipitation 4.0 JunJuly: 2.32 in precipitation 2.3 JulAugust: 1.45 in precipitation 1.4 AugSeptember: 1.37 in precipitation 1.4 SepOctober: 1.29 in precipitation 1.3 OctNovember: 0.99 in precipitation 1.0 NovDecember: 0.71 in precipitation 0.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Zortman, MT (within 1 mile); precipitation: Zortman, MT (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

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

595274b
Hays, MT · 15 mi
595244a
Dodson, MT · 18 mi
595354b
Lloyd, MT · 33 mi
595384a
Malta, MT · 34 mi
594714b
Roy, MT · 34 mi
594894b
Winifred, MT · 37 mi
595264a
Harlem, MT · 39 mi
595233b
Chinook, MT · 53 mi

Montana planting zones →

Questions about 59546

What planting zone is ZIP code 59546?

ZIP code 59546 (Zortman, 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 Zortman, MT?

The median last spring frost (32 °F) near 59546 is May 18; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Zortman station.

When is the first frost in Zortman, MT?

The median first fall frost near 59546 is September 23, giving a median frost-free growing season of 126 days.

When should I plant tomatoes in 59546?

Start tomato seeds indoors around Mar 23 – Apr 6 and set transplants outside around May 25 – Jun 8, one to three weeks after the median last frost.

How much rain and snow does 59546 get?

About 19.5 inches of precipitation a year (NOAA 1991–2020 normals, Zortman station).

How hot do summers get in Zortman, MT?

The average high peaks at 79 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 59546 have?

The USDA soil survey maps Warneke at the center of ZIP 59546: gravelly loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Zortman, MT in 2026?

Spring leaf-out near 59546 came on Mar 21 in 2026, 25 days earlier than the 1991–2020 average (Apr 15), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Zortman, MT?

Long-day onions: the longest day near 59546 is 16 h 02 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).