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

Planting zone for 59873 — Thompson Falls, MT

ZIP code 59873 (Thompson Falls, Sanders County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 7 and the first fall frost October 4.

Where ZIP 59873 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.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 7
First frostOct 4
2012 zone6a

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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Thompson Falls, 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 Thompson Falls, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 7median — 50% chance of a later frost
Safe for tender plantsMay 19only 10% chance of frost after
First fall frostOctober 4median — 10% chance by Sep 21
Growing season150 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 22 and returns around October 18.

From the NOAA station Thompson Falls Ph, MT — 6 miles away, elevation 2,379 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 59873

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 26 – Apr 9
SpinachSow outdoors · Mar 26 – Apr 16
Broccoli, cabbageStart indoors · Feb 26 – Mar 12
Broccoli, cabbageTransplant · Apr 16 – Apr 30
Onion setsPlant outdoors · Apr 9 – Apr 23
PotatoesPlant outdoors · Apr 16 – Apr 30
LettuceSow outdoors · Apr 9 – Apr 23
Carrots, beetsSow outdoors · Apr 16 – Apr 30
TomatoesStart indoors · Mar 12 – Mar 26
TomatoesTransplant · May 14 – May 28
Peppers, eggplantStart indoors · Feb 26 – Mar 12
Peppers, eggplantTransplant · May 21 – Jun 4
BeansSow outdoors · May 14 – May 28
Sweet cornSow outdoors · May 14 – May 28
Cucumbers, squashSow outdoors · May 14 – May 28
Fall lettuce, spinachSow outdoors · Aug 9 – Aug 23
GarlicPlant cloves · Sep 20 – Oct 25
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 7) and first fall frost (Oct 4) 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 59873 came on May 2 — 9 days earlier than the 1991–2020 average (May 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 6a in Montana

572 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 28

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 100

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 266

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 164

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 Thompson Falls, MT.

Soil in Thompson Falls, MT

The soil mapped at the center of ZIP 59873 is McCay — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer
pH5.0strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter70%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: McCay, cold-McCay families, complex, broadly convex ridges.

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 59873; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Thompson Falls, MT

Summer high86 °Faverage high, July
Winter low24 °Faverage low, January
Hot days39days a year at 90 °F or more
Freezing nights148nights a year at 32 °F or less
Growing degree days2,106base 50 °F — the season’s usable heat
Longest day16 h 00 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)
Precipitation22.1 inper year, rain and melted snow
Snowfall15 inper year

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 34 °F, low 24 °F 34°24° JanFebruary: average high 40 °F, low 25 °F 40°25° FebMarch: average high 49 °F, low 29 °F 49°29° MarApril: average high 58 °F, low 34 °F 58°34° AprMay: average high 68 °F, low 41 °F 68°41° MayJune: average high 75 °F, low 48 °F 75°48° JunJuly: average high 86 °F, low 53 °F 86°53° JulAugust: average high 86 °F, low 52 °F 86°52° AugSeptember: average high 75 °F, low 44 °F 75°44° SepOctober: average high 58 °F, low 36 °F 58°36° OctNovember: average high 41 °F, low 29 °F 41°29° NovDecember: average high 33 °F, low 25 °F 33°25° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 2.34 in precipitation, 2.5 in snowfall 2.3❄3 JanFebruary: 1.94 in precipitation, 0.6 in snowfall 1.9❄1 FebMarch: 1.99 in precipitation, 1.2 in snowfall 2.0❄1 MarApril: 1.65 in precipitation, 0.3 in snowfall 1.6 AprMay: 2.09 in precipitation 2.1 MayJune: 2.19 in precipitation 2.2 JunJuly: 0.88 in precipitation 0.9 JulAugust: 0.89 in precipitation 0.9 AugSeptember: 0.97 in precipitation 1.0 SepOctober: 2.16 in precipitation, 0.7 in snowfall 2.2❄1 OctNovember: 2.64 in precipitation, 2.5 in snowfall 2.6❄3 NovDecember: 2.31 in precipitation, 7.5 in snowfall 2.3❄8 Dec

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

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

598306a
De Borgia, MT · 18 mi
598746a
Trout Creek, MT · 18 mi
598676a
Saltese, MT · 23 mi
598666a
Saint Regis, MT · 23 mi
598426a
Haugan, MT · 24 mi
598596a
Plains, MT · 24 mi
838466a
Mullan, ID · 25 mi
838746a
Murray, ID · 25 mi

Montana planting zones →

Questions about 59873

What planting zone is ZIP code 59873?

ZIP code 59873 (Thompson Falls, MT) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Thompson Falls, MT?

The median last spring frost (32 °F) near 59873 is May 7; after May 19 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Thompson Falls Ph station.

When is the first frost in Thompson Falls, MT?

The median first fall frost near 59873 is October 4, giving a median frost-free growing season of 150 days.

When should I plant tomatoes in 59873?

Start tomato seeds indoors around Mar 12 – Mar 26 and set transplants outside around May 14 – May 28, one to three weeks after the median last frost.

How much rain and snow does 59873 get?

About 22.1 inches of precipitation a year and 15 inches of snowfall (NOAA 1991–2020 normals, Thompson Falls Ph station).

How hot do summers get in Thompson Falls, MT?

The average high peaks at 86 °F in July, with about 39 days a year at 90 °F or more.

What kind of soil does 59873 have?

The USDA soil survey maps McCay at the center of ZIP 59873: moderately decomposed plant material, well drained, pH about 5.0 (strongly acidic).

Did spring come early in Thompson Falls, MT in 2026?

Spring leaf-out near 59873 came on May 2 in 2026, 9 days earlier than the 1991–2020 average (May 11), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Thompson Falls, MT?

Long-day onions: the longest day near 59873 is 16 h 00 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).