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

Planting zone for 59436 — Fairfield, MT

ZIP code 59436 (Fairfield, Teton County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 13 and the first fall frost September 27.

Where ZIP 59436 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 13
First frostSep 27
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 Fairfield, 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 Fairfield, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 13median — 50% chance of a later frost
Safe for tender plantsJune 1only 10% chance of frost after
First fall frostSeptember 27median — 10% chance by Sep 14
Growing season135 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 30 and returns around October 7.

From the NOAA station Fairfield, MT — 6 miles away, elevation 3,983 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 59436

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 1 – Apr 15
SpinachSow outdoors · Apr 1 – Apr 22
Broccoli, cabbageStart indoors · Mar 4 – Mar 18
Broccoli, cabbageTransplant · Apr 22 – May 6
Onion setsPlant outdoors · Apr 15 – Apr 29
PotatoesPlant outdoors · Apr 22 – May 6
LettuceSow outdoors · Apr 15 – Apr 29
Carrots, beetsSow outdoors · Apr 22 – May 6
TomatoesStart indoors · Mar 18 – Apr 1
TomatoesTransplant · May 20 – Jun 3
Peppers, eggplantStart indoors · Mar 4 – Mar 18
Peppers, eggplantTransplant · May 27 – Jun 10
BeansSow outdoors · May 20 – Jun 3
Sweet cornSow outdoors · May 20 – Jun 3
Cucumbers, squashSow outdoors · May 20 – Jun 3
Fall lettuce, spinachSow outdoors · Aug 2 – Aug 16
GarlicPlant cloves · Sep 13 – Oct 18
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 13) and first fall frost (Sep 27) 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 59436 came on Mar 17 — 25 days earlier than the 1991–2020 average (Apr 11).

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 Fairfield, MT.

Soil in Fairfield, MT

The soil mapped at the center of ZIP 59436 is Marmarth — clay loam, well drained.

TextureClay 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 groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Marmarth-Evanston-Delpoint complex, 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 59436; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Fairfield, MT

Summer high80 °Faverage high, July
Winter low17 °Faverage low, January
Hot days8days a year at 90 °F or more
Freezing nights160nights a year at 32 °F or less
Growing degree days1,732base 50 °F — the season’s usable heat
Longest day15 h 59 mindaylight on June 21
Shortest day8 h 25 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation12.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 36 °F, low 17 °F 36°17° JanFebruary: average high 36 °F, low 17 °F 36°17° FebMarch: average high 45 °F, low 24 °F 45°24° MarApril: average high 53 °F, low 32 °F 53°32° AprMay: average high 62 °F, low 41 °F 62°41° MayJune: average high 70 °F, low 48 °F 70°48° JunJuly: average high 80 °F, low 53 °F 80°53° JulAugust: average high 79 °F, low 52 °F 79°52° AugSeptember: average high 69 °F, low 44 °F 69°44° SepOctober: average high 55 °F, low 34 °F 55°34° OctNovember: average high 43 °F, low 25 °F 43°25° NovDecember: average high 35 °F, low 18 °F 35°18° Dec

Precipitation by month inches

0″1″2″3″January: 0.34 in precipitation 0.3 JanFebruary: 0.43 in precipitation 0.4 FebMarch: 0.60 in precipitation 0.6 MarApril: 1.36 in precipitation 1.4 AprMay: 2.12 in precipitation 2.1 MayJune: 2.63 in precipitation 2.6 JunJuly: 1.08 in precipitation 1.1 JulAugust: 1.05 in precipitation 1.1 AugSeptember: 1.23 in precipitation 1.2 SepOctober: 0.74 in precipitation 0.7 OctNovember: 0.46 in precipitation 0.5 NovDecember: 0.33 in precipitation 0.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Fairfield, MT (6 mi away); precipitation: Fairfield, MT (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

594774b
Simms, MT · 14 mi
594434b
Fort Shaw, MT · 14 mi
594834a
Sun River, MT · 21 mi
594874a
Vaughn, MT · 22 mi
594224b
Choteau, MT · 23 mi
594684b
Power, MT · 24 mi
594104b
Augusta, MT · 26 mi
594194b
Bynum, MT · 26 mi

Montana planting zones →

Questions about 59436

What planting zone is ZIP code 59436?

ZIP code 59436 (Fairfield, 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 Fairfield, MT?

The median last spring frost (32 °F) near 59436 is May 13; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Fairfield station.

When is the first frost in Fairfield, MT?

The median first fall frost near 59436 is September 27, giving a median frost-free growing season of 135 days.

When should I plant tomatoes in 59436?

Start tomato seeds indoors around Mar 18 – Apr 1 and set transplants outside around May 20 – Jun 3, one to three weeks after the median last frost.

How much rain and snow does 59436 get?

About 12.4 inches of precipitation a year (NOAA 1991–2020 normals, Fairfield station).

How hot do summers get in Fairfield, MT?

The average high peaks at 80 °F in July, with about 8 days a year at 90 °F or more.

What kind of soil does 59436 have?

The USDA soil survey maps Marmarth at the center of ZIP 59436: clay loam, well drained, pH about 6.7 (neutral).

Did spring come early in Fairfield, MT in 2026?

Spring leaf-out near 59436 came on Mar 17 in 2026, 25 days earlier than the 1991–2020 average (Apr 11), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Fairfield, MT?

Long-day onions: the longest day near 59436 is 15 h 59 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).