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

Planting zone for 59645 — White Sulphur Springs, MT

ZIP code 59645 (White Sulphur Springs, Meagher County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is June 4 and the first fall frost September 11.

Where ZIP 59645 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 frostJun 4
First frostSep 11
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 White Sulphur Springs, 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 White Sulphur Springs, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJune 4median — 50% chance of a later frost
Safe for tender plantsJune 20only 10% chance of frost after
First fall frostSeptember 11median — 10% chance by Aug 27
Growing season97 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 18 and returns around September 25.

From the NOAA station White Sulphur Springs #2, MT — 12 miles away, elevation 5,040 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 59645

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 23 – May 7
SpinachSow outdoors · Apr 23 – May 14
Broccoli, cabbageStart indoors · Mar 26 – Apr 9
Broccoli, cabbageTransplant · May 14 – May 28
Onion setsPlant outdoors · May 7 – May 21
PotatoesPlant outdoors · May 14 – May 28
LettuceSow outdoors · May 7 – May 21
Carrots, beetsSow outdoors · May 14 – May 28
TomatoesStart indoors · Apr 9 – Apr 23
TomatoesTransplant · Jun 11 – Jun 25
Peppers, eggplantStart indoors · Mar 26 – Apr 9
Peppers, eggplantTransplant · Jun 18 – Jul 2
BeansSow outdoors · Jun 11 – Jun 25
Sweet cornSow outdoors · Jun 11 – Jun 25
Cucumbers, squashSow outdoors · Jun 11 – Jun 25
Fall lettuce, spinachSow outdoors · Jul 17 – Jul 31
GarlicPlant cloves · Aug 28 – Oct 2
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 4) and first fall frost (Sep 11) 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 59645 came on Apr 7 — 20 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 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 White Sulphur Springs, MT.

Soil in White Sulphur Springs, MT

The soil mapped at the center of ZIP 59645 is Tolbert — channery loam, well drained.

TextureChannery loama good balance for most vegetables
pH7.2neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Tolbert-Vershal-Absarook complex, 4 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 59645; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in White Sulphur Springs, MT

Summer high82 °Faverage high, July
Winter low13 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights199nights a year at 32 °F or less
Growing degree days1,429base 50 °F — the season’s usable heat
Longest day15 h 51 mindaylight on June 21
Shortest day8 h 33 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation13 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 33 °F, low 13 °F 33°13° JanFebruary: average high 35 °F, low 13 °F 35°13° FebMarch: average high 45 °F, low 21 °F 45°21° MarApril: average high 53 °F, low 27 °F 53°27° AprMay: average high 63 °F, low 35 °F 63°35° MayJune: average high 71 °F, low 42 °F 71°42° JunJuly: average high 82 °F, low 48 °F 82°48° JulAugust: average high 81 °F, low 47 °F 81°47° AugSeptember: average high 71 °F, low 39 °F 71°39° SepOctober: average high 56 °F, low 29 °F 56°29° OctNovember: average high 42 °F, low 20 °F 42°20° NovDecember: average high 33 °F, low 13 °F 33°13° Dec

Precipitation by month inches

0″1″2″3″January: 0.51 in precipitation 0.5 JanFebruary: 0.34 in precipitation 0.3 FebMarch: 0.71 in precipitation 0.7 MarApril: 1.44 in precipitation 1.4 AprMay: 2.08 in precipitation 2.1 MayJune: 2.52 in precipitation 2.5 JunJuly: 1.36 in precipitation 1.4 JulAugust: 1.21 in precipitation 1.2 AugSeptember: 1.04 in precipitation 1.0 SepOctober: 0.86 in precipitation 0.9 OctNovember: 0.44 in precipitation 0.4 NovDecember: 0.53 in precipitation 0.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: White Sulphur Springs #2, MT (12 mi away); precipitation: White Sulphur Springs #2, MT (12 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.

594654b
Neihart, MT · 24 mi
596444b
Townsend, MT · 26 mi
594634b
Monarch, MT · 26 mi
596424b
Ringling, MT · 32 mi
596475a
Winston, MT · 32 mi
594804b
Stockett, MT · 36 mi
594694b
Raynesford, MT · 39 mi
594214b
Cascade, MT · 40 mi

Montana planting zones →

Questions about 59645

What planting zone is ZIP code 59645?

ZIP code 59645 (White Sulphur Springs, 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 White Sulphur Springs, MT?

The median last spring frost (32 °F) near 59645 is June 4; after June 20 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, White Sulphur Springs #2 station.

When is the first frost in White Sulphur Springs, MT?

The median first fall frost near 59645 is September 11, giving a median frost-free growing season of 97 days.

When should I plant tomatoes in 59645?

Start tomato seeds indoors around Apr 9 – Apr 23 and set transplants outside around Jun 11 – Jun 25, one to three weeks after the median last frost.

How much rain and snow does 59645 get?

About 13 inches of precipitation a year (NOAA 1991–2020 normals, White Sulphur Springs #2 station).

How hot do summers get in White Sulphur Springs, MT?

The average high peaks at 82 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 59645 have?

The USDA soil survey maps Tolbert at the center of ZIP 59645: channery loam, well drained, pH about 7.2 (neutral).

Did spring come early in White Sulphur Springs, MT in 2026?

Spring leaf-out near 59645 came on Apr 7 in 2026, 20 days earlier than the 1991–2020 average (Apr 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in White Sulphur Springs, MT?

Long-day onions: the longest day near 59645 is 15 h 51 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59645 change?

Yes. The 2012 USDA map put 59645 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.