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

Planting zone for 59315 — Bloomfield, MT

ZIP code 59315 (Bloomfield, Dawson County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 12 and the first fall frost September 25.

Where ZIP 59315 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.

Zone4a−30 to −25 °F
Coldest night−34.4 to −31.7 °C
Last frostMay 12
First frostSep 25
2012 zone4a

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 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Bloomfield, 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 Bloomfield, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 12median — 50% chance of a later frost
Safe for tender plantsMay 26only 10% chance of frost after
First fall frostSeptember 25median — 10% chance by Sep 12
Growing season135 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around October 4.

From the NOAA station Savage, MT — 25 miles away, elevation 1,978 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 59315

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 31 – Apr 14
SpinachSow outdoors · Mar 31 – Apr 21
Broccoli, cabbageStart indoors · Mar 3 – Mar 17
Broccoli, cabbageTransplant · Apr 21 – May 5
Onion setsPlant outdoors · Apr 14 – Apr 28
PotatoesPlant outdoors · Apr 21 – May 5
LettuceSow outdoors · Apr 14 – Apr 28
Carrots, beetsSow outdoors · Apr 21 – May 5
TomatoesStart indoors · Mar 17 – Mar 31
TomatoesTransplant · May 19 – Jun 2
Peppers, eggplantStart indoors · Mar 3 – Mar 17
Peppers, eggplantTransplant · May 26 – Jun 9
BeansSow outdoors · May 19 – Jun 2
Sweet cornSow outdoors · May 19 – Jun 2
Cucumbers, squashSow outdoors · May 19 – Jun 2
Fall lettuce, spinachSow outdoors · Jul 31 – Aug 14
GarlicPlant cloves · Sep 11 – Oct 16
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 12) and first fall frost (Sep 25) 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 59315 came on Apr 8 — 9 days earlier than the 1991–2020 average (Apr 17).

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 4a in Montana

439 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −30 °F or colder — the bottom of zone 4a. Each links to its USDA PLANTS profile.

Trees 21

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 77

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °Falderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °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 °FBarclay's willow15 ft · high shade tolerance · to −43 °F

Wildflowers & perennials 189

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 bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °F

Grasses 141

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 Bloomfield, MT.

Soil in Bloomfield, MT

The soil mapped at the center of ZIP 59315 is Lonna — silt loam, well drained.

TextureSilt loama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2%moderate
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Lonna-Cambeth silt loams, 2 to 8 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 59315; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Bloomfield, MT

Summer high88 °Faverage high, July
Winter low7 °Faverage low, January
Hot days33days a year at 90 °F or more
Freezing nights176nights a year at 32 °F or less
Growing degree days2,610base 50 °F — the season’s usable heat
Longest day15 h 58 mindaylight on June 21
Shortest day8 h 27 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation14.6 inper year, rain and melted snow
Snowfall24 inper year

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 29 °F, low 7 °F 29°7° JanFebruary: average high 34 °F, low 11 °F 34°11° FebMarch: average high 47 °F, low 21 °F 47°21° MarApril: average high 61 °F, low 32 °F 61°32° AprMay: average high 72 °F, low 43 °F 72°43° MayJune: average high 80 °F, low 52 °F 80°52° JunJuly: average high 88 °F, low 57 °F 88°57° JulAugust: average high 88 °F, low 55 °F 88°55° AugSeptember: average high 77 °F, low 45 °F 77°45° SepOctober: average high 60 °F, low 34 °F 60°34° OctNovember: average high 44 °F, low 21 °F 44°21° NovDecember: average high 32 °F, low 11 °F 32°11° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.38 in precipitation, 4.8 in snowfall 0.4❄5 JanFebruary: 0.53 in precipitation, 4.7 in snowfall 0.5❄5 FebMarch: 0.46 in precipitation, 3.5 in snowfall 0.5❄4 MarApril: 1.44 in precipitation, 2.4 in snowfall 1.4❄2 AprMay: 2.72 in precipitation, 0.3 in snowfall 2.7 MayJune: 2.35 in precipitation 2.4 JunJuly: 2.11 in precipitation 2.1 JulAugust: 1.16 in precipitation 1.2 AugSeptember: 1.42 in precipitation 1.4 SepOctober: 1.07 in precipitation, 0.8 in snowfall 1.1❄1 OctNovember: 0.45 in precipitation, 3 in snowfall 0.5❄3 NovDecember: 0.51 in precipitation, 4.2 in snowfall 0.5❄4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Savage, MT (25 mi away); precipitation: Lindsay, MT (20 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.

592624a
Savage, MT · 18 mi
592594a
Richey, MT · 19 mi
592434a
Lambert, MT · 23 mi
593304a
Glendive, MT · 23 mi
593394b
Lindsay, MT · 25 mi
592174a
Crane, MT · 31 mi
592744a
Vida, MT · 37 mi
592704a
Sidney, MT · 38 mi

Montana planting zones →

Questions about 59315

What planting zone is ZIP code 59315?

ZIP code 59315 (Bloomfield, MT) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Bloomfield, MT?

The median last spring frost (32 °F) near 59315 is May 12; after May 26 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Savage station.

When is the first frost in Bloomfield, MT?

The median first fall frost near 59315 is September 25, giving a median frost-free growing season of 135 days.

When should I plant tomatoes in 59315?

Start tomato seeds indoors around Mar 17 – Mar 31 and set transplants outside around May 19 – Jun 2, one to three weeks after the median last frost.

How much rain and snow does 59315 get?

About 14.6 inches of precipitation a year and 24 inches of snowfall (NOAA 1991–2020 normals, Lindsay station).

How hot do summers get in Bloomfield, MT?

The average high peaks at 88 °F in July, with about 33 days a year at 90 °F or more.

What kind of soil does 59315 have?

The USDA soil survey maps Lonna at the center of ZIP 59315: silt loam, well drained, pH about 7.9 (alkaline).

Did spring come early in Bloomfield, MT in 2026?

Spring leaf-out near 59315 came on Apr 8 in 2026, 9 days earlier than the 1991–2020 average (Apr 17), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Bloomfield, MT?

Long-day onions: the longest day near 59315 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).