Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 83229 — Cobalt, ID

ZIP code 83229 (Cobalt, Lemhi County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 17 and the first fall frost September 24.

Where ZIP 83229 is

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 17

First frostSep 24

2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

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Loading the forecast for Cobalt, 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 Cobalt, ID

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 17median — 50% chance of a later frost

Safe for tender plantsJune 9only 10% chance of frost after

First fall frostSeptember 24median — 10% chance by Sep 9

Growing season127 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 2 and returns around October 5.

From the NOAA station Salmon-Ksra, ID — 18 miles away, elevation 3,954 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 83229

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 5 – Apr 19

SpinachSow outdoors · Apr 5 – Apr 26

Broccoli, cabbageStart indoors · Mar 8 – Mar 22

Broccoli, cabbageTransplant · Apr 26 – May 10

Onion setsPlant outdoors · Apr 19 – May 3

PotatoesPlant outdoors · Apr 26 – May 10

LettuceSow outdoors · Apr 19 – May 3

Carrots, beetsSow outdoors · Apr 26 – May 10

TomatoesStart indoors · Mar 22 – Apr 5

TomatoesTransplant · May 24 – Jun 7

Peppers, eggplantStart indoors · Mar 8 – Mar 22

Peppers, eggplantTransplant · May 31 – Jun 14

BeansSow outdoors · May 24 – Jun 7

Sweet cornSow outdoors · May 24 – Jun 7

Cucumbers, squashSow outdoors · May 24 – Jun 7

Fall lettuce, spinachSow outdoors · Jul 30 – Aug 13

GarlicPlant cloves · Sep 10 – Oct 15

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 17) and first fall frost (Sep 24) 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 83229 came on Apr 22 — 9 days earlier than the 1991–2020 average (May 1).

average
May 12026
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).

Soil in Cobalt, ID

The soil mapped at the center of ZIP 83229 is Bradshaw family — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables

pH7.2neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupBwater soaks in moderately

Farmland classPrime farmland if drained and either protected from flooding or not frequently flooded during the growing seasonUSDA classification

Map unit: Bradshaw family, stony surface-Oxyaquic Xerofluvents family, occasionally flooded-Fluventic Endoaquepts family, frequently flooded, complex, 0 to 4 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 83229; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cobalt, ID

Summer high86 °Faverage high, July

Winter low11 °Faverage low, January

Hot days25days a year at 90 °F or more

Freezing nights180nights a year at 32 °F or less

Growing degree days1,911base 50 °F — the season’s usable heat

Longest day15 h 38 mindaylight on June 21

Shortest day8 h 45 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation24.1 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Salmon-Ksra, ID (18 mi away); precipitation: Morgan Creek, ID (17 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

North Fork, ID · 24 mi

Gibbonsville, ID · 35 mi

Idaho planting zones →

Questions about 83229

What planting zone is ZIP code 83229?

ZIP code 83229 (Cobalt, 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 Cobalt, ID?

The median last spring frost (32 °F) near 83229 is May 17; after June 9 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Salmon-Ksra station.

When is the first frost in Cobalt, ID?

The median first fall frost near 83229 is September 24, giving a median frost-free growing season of 127 days.

When should I plant tomatoes in 83229?

Start tomato seeds indoors around Mar 22 – Apr 5 and set transplants outside around May 24 – Jun 7, one to three weeks after the median last frost.

How much rain and snow does 83229 get?

About 24.1 inches of precipitation a year (NOAA 1991–2020 normals, Morgan Creek station).

How hot do summers get in Cobalt, ID?

The average high peaks at 86 °F in July, with about 25 days a year at 90 °F or more.

What kind of soil does 83229 have?

The USDA soil survey maps Bradshaw family at the center of ZIP 83229: gravelly loam, well drained, pH about 7.2 (neutral).

Did spring come early in Cobalt, ID in 2026?

Spring leaf-out near 83229 came on Apr 22 in 2026, 9 days earlier than the 1991–2020 average (May 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Cobalt, ID?

Long-day onions: the longest day near 83229 is 15 h 38 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 83229 change?

Yes. The 2012 USDA map put 83229 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.