Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 30, 2026

Planting zone for 83428 — Irwin, ID

ZIP code 83428 (Irwin, Bonneville County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is June 13 and the first fall frost September 9.

Where ZIP 83428 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 frostJun 13

First frostSep 9

2012 zone5a

Was 5a on the 2012 map — a full zone warmer now. 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 Irwin, 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 Irwin, ID

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 13median — 50% chance of a later frost

Safe for tender plantsJune 28only 10% chance of frost after

First fall frostSeptember 9median — 10% chance by Aug 26

Growing season86 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 22 and returns around September 20.

From the NOAA station Driggs, ID — 24 miles away, elevation 6,119 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 83428

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · May 2 – May 16

SpinachSow outdoors · May 2 – May 23

Broccoli, cabbageStart indoors · Apr 4 – Apr 18

Broccoli, cabbageTransplant · May 23 – Jun 6

Onion setsPlant outdoors · May 16 – May 30

PotatoesPlant outdoors · May 23 – Jun 6

LettuceSow outdoors · May 16 – May 30

Carrots, beetsSow outdoors · May 23 – Jun 6

TomatoesStart indoors · Apr 18 – May 2

TomatoesTransplant · Jun 20 – Jul 4

Peppers, eggplantStart indoors · Apr 4 – Apr 18

Peppers, eggplantTransplant · Jun 27 – Jul 11

BeansSow outdoors · Jun 20 – Jul 4

Sweet cornSow outdoors · Jun 20 – Jul 4

Cucumbers, squashSow outdoors · Jun 20 – Jul 4

Fall lettuce, spinachSow outdoors · Jul 15 – Jul 29

GarlicPlant cloves · Aug 26 – Sep 30

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 13) and first fall frost (Sep 9) 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 83428 came on May 12 — 7 days earlier than the 1991–2020 average (May 19).

average
May 192026
May 12

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 Idaho

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

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 Irwin, ID.

Soil in Irwin, ID

The soil mapped at the center of ZIP 83428 is Yodal — gravelly loam, well drained.

TextureGravelly loama good balance for most vegetables

pH6.1slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter4.5%moderate

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Yodal gravelly loam, 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 83428; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Irwin, ID

Summer high85 °Faverage high, July

Winter low11 °Faverage low, January

Hot days14days a year at 90 °F or more

Freezing nights198nights a year at 32 °F or less

Growing degree days1,519base 50 °F — the season’s usable heat

Longest day15 h 25 mindaylight on June 21

Shortest day8 h 57 mindaylight on December 21

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

Precipitation20.1 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: Swan Valley, ID (9 mi away); precipitation: Swan Valley, ID (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

830145b

Wilson, WY · 9 mi

834496a

Swan Valley, ID · 12 mi

Teton Village, WY · 20 mi

Idaho planting zones →

Questions about 83428

What planting zone is ZIP code 83428?

ZIP code 83428 (Irwin, ID) 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 Irwin, ID?

The median last spring frost (32 °F) near 83428 is June 13; after June 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Driggs station.

When is the first frost in Irwin, ID?

The median first fall frost near 83428 is September 9, giving a median frost-free growing season of 86 days.

When should I plant tomatoes in 83428?

Start tomato seeds indoors around Apr 18 – May 2 and set transplants outside around Jun 20 – Jul 4, one to three weeks after the median last frost.

How much rain and snow does 83428 get?

About 20.1 inches of precipitation a year (NOAA 1991–2020 normals, Swan Valley station).

How hot do summers get in Irwin, ID?

The average high peaks at 85 °F in July, with about 14 days a year at 90 °F or more.

What kind of soil does 83428 have?

The USDA soil survey maps Yodal at the center of ZIP 83428: gravelly loam, well drained, pH about 6.1 (slightly acidic).

Did spring come early in Irwin, ID in 2026?

Spring leaf-out near 83428 came on May 12 in 2026, 7 days earlier than the 1991–2020 average (May 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Irwin, ID?

Long-day onions: the longest day near 83428 is 15 h 25 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 83428 change?

Yes. The 2012 USDA map put 83428 in zone 5a; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.