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

Planting zone for 83539 — Kooskia, ID

ZIP code 83539 (Kooskia, Idaho County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 31 and the first fall frost September 12.

Where ZIP 83539 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.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostMay 31
First frostSep 12
2012 zone6b

Was 6b on the 2012 map — a full zone colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Kooskia, ID…

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 Kooskia, ID

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 31median — 50% chance of a later frost
Safe for tender plantsJune 26only 10% chance of frost after
First fall frostSeptember 12median — 10% chance by Aug 28
Growing season102 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 9 and returns around September 30.

From the NOAA station Powell, ID — 19 miles away, elevation 3,530 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 83539

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 19 – May 3
SpinachSow outdoors · Apr 19 – May 10
Broccoli, cabbageStart indoors · Mar 22 – Apr 5
Broccoli, cabbageTransplant · May 10 – May 24
Onion setsPlant outdoors · May 3 – May 17
PotatoesPlant outdoors · May 10 – May 24
LettuceSow outdoors · May 3 – May 17
Carrots, beetsSow outdoors · May 10 – May 24
TomatoesStart indoors · Apr 5 – Apr 19
TomatoesTransplant · Jun 7 – Jun 21
Peppers, eggplantStart indoors · Mar 22 – Apr 5
Peppers, eggplantTransplant · Jun 14 – Jun 28
BeansSow outdoors · Jun 7 – Jun 21
Sweet cornSow outdoors · Jun 7 – Jun 21
Cucumbers, squashSow outdoors · Jun 7 – Jun 21
Fall lettuce, spinachSow outdoors · Jul 18 – Aug 1
GarlicPlant cloves · Aug 29 – Oct 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 31) and first fall frost (Sep 12) 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 83539 came on May 3 — about the same time as the 1991–2020 average (May 1).

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).

Soil in Kooskia, ID

The soil mapped at the center of ZIP 83539 is Vitrandic Haplocryepts — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH5.0strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Vitrandic Haplocryepts, granitics-Andic Haplocryepts, glaciated association.

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 83539; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Kooskia, ID

Summer high83 °Faverage high, July
Winter low18 °Faverage low, January
Hot days18days a year at 90 °F or more
Freezing nights219nights a year at 32 °F or less
Growing degree days1,325base 50 °F — the season’s usable heat
Longest day15 h 47 mindaylight on June 21
Shortest day8 h 36 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation46.2 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 32 °F, low 18 °F 32°18° JanFebruary: average high 37 °F, low 18 °F 37°18° FebMarch: average high 46 °F, low 24 °F 46°24° MarApril: average high 53 °F, low 29 °F 53°29° AprMay: average high 64 °F, low 35 °F 64°35° MayJune: average high 71 °F, low 42 °F 71°42° JunJuly: average high 83 °F, low 46 °F 83°46° JulAugust: average high 82 °F, low 44 °F 82°44° AugSeptember: average high 71 °F, low 37 °F 71°37° SepOctober: average high 54 °F, low 30 °F 54°30° OctNovember: average high 38 °F, low 24 °F 38°24° NovDecember: average high 30 °F, low 18 °F 30°18° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 5.32 in precipitation 5.3 JanFebruary: 4.65 in precipitation 4.7 FebMarch: 5.07 in precipitation 5.1 MarApril: 4.04 in precipitation 4.0 AprMay: 3.44 in precipitation 3.4 MayJune: 3.16 in precipitation 3.2 JunJuly: 1.30 in precipitation 1.3 JulAugust: 1.43 in precipitation 1.4 AugSeptember: 2.03 in precipitation 2.0 SepOctober: 4.08 in precipitation 4.1 OctNovember: 5.69 in precipitation 5.7 NovDecember: 5.99 in precipitation 6.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Powell, ID (19 mi away); precipitation: Savage Pass, ID (18 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

598755b
Victor, MT · 28 mi
598415b
Pinesdale, MT · 30 mi
598355b
Grantsdale, MT · 34 mi
598405b
Hamilton, MT · 36 mi
598475b
Lolo, MT · 39 mi
598705b
Stevensville, MT · 41 mi
598275b
Conner, MT · 44 mi
835255b
Elk City, ID · 44 mi

Idaho planting zones →

Questions about 83539

What planting zone is ZIP code 83539?

ZIP code 83539 (Kooskia, ID) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Kooskia, ID?

The median last spring frost (32 °F) near 83539 is May 31; after June 26 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Powell station.

When is the first frost in Kooskia, ID?

The median first fall frost near 83539 is September 12, giving a median frost-free growing season of 102 days.

When should I plant tomatoes in 83539?

Start tomato seeds indoors around Apr 5 – Apr 19 and set transplants outside around Jun 7 – Jun 21, one to three weeks after the median last frost.

How much rain and snow does 83539 get?

About 46.2 inches of precipitation a year (NOAA 1991–2020 normals, Savage Pass station).

How hot do summers get in Kooskia, ID?

The average high peaks at 83 °F in July, with about 18 days a year at 90 °F or more.

What kind of soil does 83539 have?

The USDA soil survey maps Vitrandic Haplocryepts at the center of ZIP 83539: slightly decomposed plant material, well drained, pH about 5.0 (strongly acidic).

Did spring come early in Kooskia, ID in 2026?

Spring leaf-out near 83539 came on May 3 in 2026, about the same as the 1991–2020 average (May 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Kooskia, ID?

Long-day onions: the longest day near 83539 is 15 h 47 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 83539 change?

Yes. The 2012 USDA map put 83539 in zone 6b; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.