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

Planting zone for 59638 — Jefferson City, MT

ZIP code 59638 (Jefferson City, Jefferson County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is June 18 and the first fall frost September 5.

Where ZIP 59638 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 frostJun 18
First frostSep 5
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 Jefferson City, 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 Jefferson City, MT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJune 18median — 50% chance of a later frost
Safe for tender plantsJuly 3only 10% chance of frost after
First fall frostSeptember 5median — 10% chance by Aug 21
Growing season81 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 29 and returns around September 18.

From the NOAA station Tizer Gardens, MT — within 1 mile, elevation 4,672 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 59638

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · May 7 – May 21
SpinachSow outdoors · May 7 – May 28
Broccoli, cabbageStart indoors · Apr 9 – Apr 23
Broccoli, cabbageTransplant · May 28 – Jun 11
Onion setsPlant outdoors · May 21 – Jun 4
PotatoesPlant outdoors · May 28 – Jun 11
LettuceSow outdoors · May 21 – Jun 4
Carrots, beetsSow outdoors · May 28 – Jun 11
TomatoesStart indoors · Apr 23 – May 7
TomatoesTransplant · Jun 25 – Jul 9
Peppers, eggplantStart indoors · Apr 9 – Apr 23
Peppers, eggplantTransplant · Jul 2 – Jul 16
BeansSow outdoors · Jun 25 – Jul 9
Sweet cornSow outdoors · Jun 25 – Jul 9
Cucumbers, squashSow outdoors · Jun 25 – Jul 9
Fall lettuce, spinachSow outdoors · Jul 11 – Jul 25
GarlicPlant cloves · Aug 22 – Sep 26
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 18) and first fall frost (Sep 5) 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 59638 came on Mar 24 — 29 days earlier than the 1991–2020 average (Apr 22).

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 Jefferson City, MT.

Soil in Jefferson City, MT

The soil mapped at the center of ZIP 59638 is Kadygulch — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables
pH6.7neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Kadygulch-Roegulch, stony, complex, 35 to 60 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 59638; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Jefferson City, MT

Summer high82 °Faverage high, August
Winter low10 °Faverage low, January
Hot days11days a year at 90 °F or more
Freezing nights223nights a year at 32 °F or less
Growing degree days1,209base 50 °F — the season’s usable heat
Longest day15 h 48 mindaylight on June 21
Shortest day8 h 35 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation17.8 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 35 °F, low 10 °F 35°10° JanFebruary: average high 36 °F, low 11 °F 36°11° FebMarch: average high 46 °F, low 18 °F 46°18° MarApril: average high 54 °F, low 25 °F 54°25° AprMay: average high 62 °F, low 33 °F 62°33° MayJune: average high 71 °F, low 39 °F 71°39° JunJuly: average high 81 °F, low 44 °F 81°44° JulAugust: average high 82 °F, low 43 °F 82°43° AugSeptember: average high 71 °F, low 35 °F 71°35° SepOctober: average high 56 °F, low 26 °F 56°26° OctNovember: average high 43 °F, low 19 °F 43°19° NovDecember: average high 33 °F, low 10 °F 33°10° Dec

Precipitation by month inches

0″1″2″3″4″January: 0.80 in precipitation 0.8 JanFebruary: 0.81 in precipitation 0.8 FebMarch: 1.04 in precipitation 1.0 MarApril: 2.03 in precipitation 2.0 AprMay: 2.76 in precipitation 2.8 MayJune: 3.13 in precipitation 3.1 JunJuly: 1.39 in precipitation 1.4 JulAugust: 1.31 in precipitation 1.3 AugSeptember: 1.42 in precipitation 1.4 SepOctober: 1.34 in precipitation 1.3 OctNovember: 0.93 in precipitation 0.9 NovDecember: 0.86 in precipitation 0.9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Tizer Gardens, MT (within 1 mile); precipitation: Tizer Gardens, MT (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

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

596344b
Clancy, MT · 6 mi
596325a
Boulder, MT · 13 mi
596014b
Helena, MT · 14 mi
596235a
Helena, MT · 16 mi
596205a
Helena, MT · 16 mi
596245a
Helena, MT · 16 mi
596264b
Helena, MT · 16 mi
596355a
East Helena, MT · 17 mi

Montana planting zones →

Questions about 59638

What planting zone is ZIP code 59638?

ZIP code 59638 (Jefferson City, 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 Jefferson City, MT?

The median last spring frost (32 °F) near 59638 is June 18; after July 3 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Tizer Gardens station.

When is the first frost in Jefferson City, MT?

The median first fall frost near 59638 is September 5, giving a median frost-free growing season of 81 days.

When should I plant tomatoes in 59638?

Start tomato seeds indoors around Apr 23 – May 7 and set transplants outside around Jun 25 – Jul 9, one to three weeks after the median last frost.

How much rain and snow does 59638 get?

About 17.8 inches of precipitation a year (NOAA 1991–2020 normals, Tizer Gardens station).

How hot do summers get in Jefferson City, MT?

The average high peaks at 82 °F in August, with about 11 days a year at 90 °F or more.

What kind of soil does 59638 have?

The USDA soil survey maps Kadygulch at the center of ZIP 59638: gravelly loam, well drained, pH about 6.7 (neutral).

Did spring come early in Jefferson City, MT in 2026?

Spring leaf-out near 59638 came on Mar 24 in 2026, 29 days earlier than the 1991–2020 average (Apr 22), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Jefferson City, MT?

Long-day onions: the longest day near 59638 is 15 h 48 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).