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

Planting zone for 59441 — Forest Grove, MT

ZIP code 59441 (Forest Grove, Fergus County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 19 and the first fall frost September 25.

Where ZIP 59441 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 19
First frostSep 25
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 Forest Grove, 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 Forest Grove, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 19median — 50% chance of a later frost
Safe for tender plantsJune 1only 10% chance of frost after
First fall frostSeptember 25median — 10% chance by Sep 11
Growing season128 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 7 and returns around October 5.

From the NOAA station Lewistown 11ese, MT — 14 miles away, elevation 5,030 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 59441

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 7 – Apr 21
SpinachSow outdoors · Apr 7 – Apr 28
Broccoli, cabbageStart indoors · Mar 10 – Mar 24
Broccoli, cabbageTransplant · Apr 28 – May 12
Onion setsPlant outdoors · Apr 21 – May 5
PotatoesPlant outdoors · Apr 28 – May 12
LettuceSow outdoors · Apr 21 – May 5
Carrots, beetsSow outdoors · Apr 28 – May 12
TomatoesStart indoors · Mar 24 – Apr 7
TomatoesTransplant · May 26 – Jun 9
Peppers, eggplantStart indoors · Mar 10 – Mar 24
Peppers, eggplantTransplant · Jun 2 – Jun 16
BeansSow outdoors · May 26 – Jun 9
Sweet cornSow outdoors · May 26 – Jun 9
Cucumbers, squashSow outdoors · May 26 – Jun 9
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 19) 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 59441 came on Mar 24 — 26 days earlier than the 1991–2020 average (Apr 19).

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 Forest Grove, MT.

Soil in Forest Grove, MT

The soil mapped at the center of ZIP 59441 is Kildor — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH7.0neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3.5%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Kildor-Skaggs-Hanson complex, 15 to 45 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 59441; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Forest Grove, MT

Summer high78 °Faverage high, August
Winter low15 °Faverage low, January
Hot days4days a year at 90 °F or more
Freezing nights172nights a year at 32 °F or less
Growing degree days1,598base 50 °F — the season’s usable heat
Longest day15 h 52 mindaylight on June 21
Shortest day8 h 32 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation20.9 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 15 °F 33°15° JanFebruary: average high 33 °F, low 15 °F 33°15° FebMarch: average high 41 °F, low 22 °F 41°22° MarApril: average high 49 °F, low 29 °F 49°29° AprMay: average high 59 °F, low 38 °F 59°38° MayJune: average high 67 °F, low 46 °F 67°46° JunJuly: average high 77 °F, low 54 °F 77°54° JulAugust: average high 78 °F, low 53 °F 78°53° AugSeptember: average high 67 °F, low 44 °F 67°44° SepOctober: average high 53 °F, low 34 °F 53°34° OctNovember: average high 39 °F, low 24 °F 39°24° NovDecember: average high 34 °F, low 17 °F 34°17° Dec

Precipitation by month inches

0″1″2″3″4″January: 0.76 in precipitation 0.8 JanFebruary: 0.88 in precipitation 0.9 FebMarch: 1.19 in precipitation 1.2 MarApril: 2.07 in precipitation 2.1 AprMay: 3.78 in precipitation 3.8 MayJune: 3.55 in precipitation 3.5 JunJuly: 1.87 in precipitation 1.9 JulAugust: 1.75 in precipitation 1.8 AugSeptember: 1.68 in precipitation 1.7 SepOctober: 1.54 in precipitation 1.5 OctNovember: 1.03 in precipitation 1.0 NovDecember: 0.85 in precipitation 0.8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Lewistown 11ese, MT (14 mi away); precipitation: Lewistown 11ese, MT (14 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 4b.

590324b
Grass Range, MT · 22 mi
594574b
Lewistown, MT · 24 mi
594644b
Moore, MT · 26 mi
590844b
Teigen, MT · 27 mi
594534b
Judith Gap, MT · 32 mi
590724b
Roundup, MT · 32 mi
590464b
Lavina, MT · 33 mi
590744b
Ryegate, MT · 34 mi

Montana planting zones →

Questions about 59441

What planting zone is ZIP code 59441?

ZIP code 59441 (Forest Grove, 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 Forest Grove, MT?

The median last spring frost (32 °F) near 59441 is May 19; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lewistown 11ese station.

When is the first frost in Forest Grove, MT?

The median first fall frost near 59441 is September 25, giving a median frost-free growing season of 128 days.

When should I plant tomatoes in 59441?

Start tomato seeds indoors around Mar 24 – Apr 7 and set transplants outside around May 26 – Jun 9, one to three weeks after the median last frost.

How much rain and snow does 59441 get?

About 20.9 inches of precipitation a year (NOAA 1991–2020 normals, Lewistown 11ese station).

How hot do summers get in Forest Grove, MT?

The average high peaks at 78 °F in August, with about 4 days a year at 90 °F or more.

What kind of soil does 59441 have?

The USDA soil survey maps Kildor at the center of ZIP 59441: clay loam, well drained, pH about 7.0 (neutral).

Did spring come early in Forest Grove, MT in 2026?

Spring leaf-out near 59441 came on Mar 24 in 2026, 26 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Forest Grove, MT?

Long-day onions: the longest day near 59441 is 15 h 52 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).