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

Planting zone for 59073 — Roundup, MT

ZIP code 59073 (Roundup, Musselshell County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 20 and the first fall frost September 21.

Where ZIP 59073 is

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 20
First frostSep 21
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 Roundup, 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 Roundup, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 20median — 50% chance of a later frost
Safe for tender plantsJune 2only 10% chance of frost after
First fall frostSeptember 21median — 10% chance by Sep 5
Growing season124 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 7 and returns around October 1.

From the NOAA station Roundup, MT — within 1 mile, elevation 3,199 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 59073

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 8 – Apr 22
SpinachSow outdoors · Apr 8 – Apr 29
Broccoli, cabbageStart indoors · Mar 11 – Mar 25
Broccoli, cabbageTransplant · Apr 29 – May 13
Onion setsPlant outdoors · Apr 22 – May 6
PotatoesPlant outdoors · Apr 29 – May 13
LettuceSow outdoors · Apr 22 – May 6
Carrots, beetsSow outdoors · Apr 29 – May 13
TomatoesStart indoors · Mar 25 – Apr 8
TomatoesTransplant · May 27 – Jun 10
Peppers, eggplantStart indoors · Mar 11 – Mar 25
Peppers, eggplantTransplant · Jun 3 – Jun 17
BeansSow outdoors · May 27 – Jun 10
Sweet cornSow outdoors · May 27 – Jun 10
Cucumbers, squashSow outdoors · May 27 – Jun 10
Fall lettuce, spinachSow outdoors · Jul 27 – Aug 10
GarlicPlant cloves · Sep 7 – Oct 12
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 20) and first fall frost (Sep 21) 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 59073 came on Mar 11 — 24 days earlier than the 1991–2020 average (Apr 4).

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 Roundup, MT.

Soil in Roundup, MT

The center of ZIP 59073 is mapped as Urban land: 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 59073; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Roundup, MT

Summer high89 °Faverage high, July
Winter low13 °Faverage low, January
Hot days44days a year at 90 °F or more
Freezing nights163nights a year at 32 °F or less
Growing degree days2,260base 50 °F — the season’s usable heat
Longest day15 h 49 mindaylight on June 21
Shortest day8 h 35 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation14.9 inper year, rain and melted snow
Snowfall24 inper year; 31 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 37 °F, low 13 °F 37°13° JanFebruary: average high 41 °F, low 15 °F 41°15° FebMarch: average high 51 °F, low 22 °F 51°22° MarApril: average high 60 °F, low 30 °F 60°30° AprMay: average high 69 °F, low 39 °F 69°39° MayJune: average high 78 °F, low 48 °F 78°48° JunJuly: average high 89 °F, low 54 °F 89°54° JulAugust: average high 88 °F, low 51 °F 88°51° AugSeptember: average high 77 °F, low 42 °F 77°42° SepOctober: average high 61 °F, low 32 °F 61°32° OctNovember: average high 47 °F, low 22 °F 47°22° NovDecember: average high 37 °F, low 14 °F 37°14° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.37 in precipitation, 5.2 in snowfall 0.4❄5 JanFebruary: 0.42 in precipitation, 3.9 in snowfall 0.4❄4 FebMarch: 0.71 in precipitation, 4.4 in snowfall 0.7❄4 MarApril: 1.71 in precipitation, 1.4 in snowfall 1.7❄1 AprMay: 2.55 in precipitation, 0.1 in snowfall 2.5 MayJune: 2.89 in precipitation 2.9 JunJuly: 1.70 in precipitation 1.7 JulAugust: 1.21 in precipitation 1.2 AugSeptember: 1.20 in precipitation 1.2 SepOctober: 1.22 in precipitation, 1 in snowfall 1.2❄1 OctNovember: 0.49 in precipitation, 2.8 in snowfall 0.5❄3 NovDecember: 0.41 in precipitation, 5.6 in snowfall 0.4❄6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Roundup, MT (within 1 mile); precipitation: Roundup, MT (within 1 mile). 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.

590724b
Roundup, MT · 6 mi
590464b
Lavina, MT · 20 mi
590594b
Musselshell, MT · 23 mi
590794b
Shepherd, MT · 28 mi
590154b
Broadview, MT · 28 mi
590025a
Acton, MT · 30 mi
590884b
Worden, MT · 32 mi
594414b
Forest Grove, MT · 36 mi

All 2 ZIP codes in Roundup → · Montana planting zones →

Questions about 59073

What planting zone is ZIP code 59073?

ZIP code 59073 (Roundup, 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 Roundup, MT?

The median last spring frost (32 °F) near 59073 is May 20; after June 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Roundup station.

When is the first frost in Roundup, MT?

The median first fall frost near 59073 is September 21, giving a median frost-free growing season of 124 days.

When should I plant tomatoes in 59073?

Start tomato seeds indoors around Mar 25 – Apr 8 and set transplants outside around May 27 – Jun 10, one to three weeks after the median last frost.

How much rain and snow does 59073 get?

About 14.9 inches of precipitation a year and 24 inches of snowfall (NOAA 1991–2020 normals, Roundup station).

How hot do summers get in Roundup, MT?

The average high peaks at 89 °F in July, with about 44 days a year at 90 °F or more.

Did spring come early in Roundup, MT in 2026?

Spring leaf-out near 59073 came on Mar 11 in 2026, 24 days earlier than the 1991–2020 average (Apr 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Roundup, MT?

Long-day onions: the longest day near 59073 is 15 h 49 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).