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

Planting zone for 59721 — Cardwell, MT

ZIP code 59721 (Cardwell, Jefferson County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 9 and the first fall frost September 27.

Where ZIP 59721 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.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostMay 9
First frostSep 27
2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Cardwell, 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 Cardwell, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 9median — 50% chance of a later frost
Safe for tender plantsMay 24only 10% chance of frost after
First fall frostSeptember 27median — 10% chance by Sep 12
Growing season139 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 29 and returns around October 6.

From the NOAA station Trident, MT — 20 miles away, elevation 4,036 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 59721

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 28 – Apr 11
SpinachSow outdoors · Mar 28 – Apr 18
Broccoli, cabbageStart indoors · Feb 28 – Mar 14
Broccoli, cabbageTransplant · Apr 18 – May 2
Onion setsPlant outdoors · Apr 11 – Apr 25
PotatoesPlant outdoors · Apr 18 – May 2
LettuceSow outdoors · Apr 11 – Apr 25
Carrots, beetsSow outdoors · Apr 18 – May 2
TomatoesStart indoors · Mar 14 – Mar 28
TomatoesTransplant · May 16 – May 30
Peppers, eggplantStart indoors · Feb 28 – Mar 14
Peppers, eggplantTransplant · May 23 – Jun 6
BeansSow outdoors · May 16 – May 30
Sweet cornSow outdoors · May 16 – May 30
Cucumbers, squashSow outdoors · May 16 – May 30
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 9) 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 59721 came on Mar 23 — 24 days earlier than the 1991–2020 average (Apr 16).

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 5a in Montana

548 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 26

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 96

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 253

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 161

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 Cardwell, MT.

Soil in Cardwell, MT

The soil mapped at the center of ZIP 59721 is Whitlash — very channery coarse sandy loam, well drained.

TextureVery channery coarse sandy loamdrains and warms fast; dries out and needs more feeding
pH6.7neutral; 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: Whitlash, very stony-Brickner, stony-Rock outcrop complex, 4 to 25 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 59721; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cardwell, MT

Summer high85 °Faverage high, July
Winter low15 °Faverage low, December
Hot days25days a year at 90 °F or more
Freezing nights174nights a year at 32 °F or less
Growing degree days1,997base 50 °F — the season’s usable heat
Longest day15 h 44 mindaylight on June 21
Shortest day8 h 39 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation38.3 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 33 °F, low 16 °F 33°16° JanFebruary: average high 37 °F, low 18 °F 37°18° FebMarch: average high 48 °F, low 26 °F 48°26° MarApril: average high 56 °F, low 33 °F 56°33° AprMay: average high 66 °F, low 42 °F 66°42° MayJune: average high 74 °F, low 49 °F 74°49° JunJuly: average high 85 °F, low 54 °F 85°54° JulAugust: average high 84 °F, low 51 °F 84°51° AugSeptember: average high 73 °F, low 43 °F 73°43° SepOctober: average high 58 °F, low 33 °F 58°33° OctNovember: average high 42 °F, low 23 °F 42°23° NovDecember: average high 33 °F, low 15 °F 33°15° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 2.43 in precipitation 2.4 JanFebruary: 2.73 in precipitation 2.7 FebMarch: 3.69 in precipitation 3.7 MarApril: 5.09 in precipitation 5.1 AprMay: 5.35 in precipitation 5.3 MayJune: 4.23 in precipitation 4.2 JunJuly: 1.43 in precipitation 1.4 JulAugust: 1.66 in precipitation 1.7 AugSeptember: 2.27 in precipitation 2.3 SepOctober: 3.55 in precipitation 3.5 OctNovember: 2.89 in precipitation 2.9 NovDecember: 3.00 in precipitation 3.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Trident, MT (20 mi away); precipitation: Albro Lake, MT (18 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

597475a
Pony, MT · 12 mi
597355a
Harrison, MT · 14 mi
597595a
Whitehall, MT · 15 mi
597605a
Willow Creek, MT · 15 mi
597525a
Three Forks, MT · 17 mi
597455a
Norris, MT · 21 mi
596325a
Boulder, MT · 23 mi
596435a
Toston, MT · 24 mi

Montana planting zones →

Questions about 59721

What planting zone is ZIP code 59721?

ZIP code 59721 (Cardwell, MT) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Cardwell, MT?

The median last spring frost (32 °F) near 59721 is May 9; after May 24 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Trident station.

When is the first frost in Cardwell, MT?

The median first fall frost near 59721 is September 27, giving a median frost-free growing season of 139 days.

When should I plant tomatoes in 59721?

Start tomato seeds indoors around Mar 14 – Mar 28 and set transplants outside around May 16 – May 30, one to three weeks after the median last frost.

How much rain and snow does 59721 get?

About 38.3 inches of precipitation a year (NOAA 1991–2020 normals, Albro Lake station).

How hot do summers get in Cardwell, MT?

The average high peaks at 85 °F in July, with about 25 days a year at 90 °F or more.

What kind of soil does 59721 have?

The USDA soil survey maps Whitlash at the center of ZIP 59721: very channery coarse sandy loam, well drained, pH about 6.7 (neutral).

Did spring come early in Cardwell, MT in 2026?

Spring leaf-out near 59721 came on Mar 23 in 2026, 24 days earlier than the 1991–2020 average (Apr 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Cardwell, MT?

Long-day onions: the longest day near 59721 is 15 h 44 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59721 change?

Yes. The 2012 USDA map put 59721 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.