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

Planting zone for 82430 — Kirby, WY

ZIP code 82430 (Kirby, Hot Springs County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 24 and the first fall frost September 16.

Where ZIP 82430 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 frostMay 24
First frostSep 16
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 Kirby, WY…

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 Kirby, WY

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 24median — 50% chance of a later frost
Safe for tender plantsJune 9only 10% chance of frost after
First fall frostSeptember 16median — 10% chance by Sep 4
Growing season112 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around September 24.

From the NOAA station Thermopolis 9ne, WY — 4 miles away, elevation 4,282 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 82430

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 12 – Apr 26
SpinachSow outdoors · Apr 12 – May 3
Broccoli, cabbageStart indoors · Mar 15 – Mar 29
Broccoli, cabbageTransplant · May 3 – May 17
Onion setsPlant outdoors · Apr 26 – May 10
PotatoesPlant outdoors · May 3 – May 17
LettuceSow outdoors · Apr 26 – May 10
Carrots, beetsSow outdoors · May 3 – May 17
TomatoesStart indoors · Mar 29 – Apr 12
TomatoesTransplant · May 31 – Jun 14
Peppers, eggplantStart indoors · Mar 15 – Mar 29
Peppers, eggplantTransplant · Jun 7 – Jun 21
BeansSow outdoors · May 31 – Jun 14
Sweet cornSow outdoors · May 31 – Jun 14
Cucumbers, squashSow outdoors · May 31 – Jun 14
Fall lettuce, spinachSow outdoors · Jul 22 – Aug 5
GarlicPlant cloves · Sep 2 – Oct 7
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 24) and first fall frost (Sep 16) 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 82430 came on Mar 21 — 18 days earlier than the 1991–2020 average (Apr 8).

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 Wyoming

495 plants native to the lower 48 states, recorded in Wyoming, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 22

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 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °FDouglas-fir200 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 83

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 226

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 152

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 Kirby, WY.

Soil in Kirby, WY

The center of ZIP 82430 is mapped as No Digital Data Available: built-over ground without natural soil data. Garden soil here is usually imported or disturbed — test before you plant.

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 82430; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Kirby, WY

Summer high88 °Faverage high, July
Winter low0 °Faverage low, January
Hot days34days a year at 90 °F or more
Freezing nights211nights a year at 32 °F or less
Growing degree days1,890base 50 °F — the season’s usable heat
Longest day15 h 28 mindaylight on June 21
Shortest day8 h 54 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation12.6 inper year, rain and melted snow
Snowfall51 inper year; 88 days with snow on the ground

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 31 °F, low 0 °F 31°0° JanFebruary: average high 38 °F, low 8 °F 38°8° FebMarch: average high 50 °F, low 19 °F 50°19° MarApril: average high 59 °F, low 27 °F 59°27° AprMay: average high 68 °F, low 37 °F 68°37° MayJune: average high 78 °F, low 45 °F 78°45° JunJuly: average high 88 °F, low 51 °F 88°51° JulAugust: average high 86 °F, low 48 °F 86°48° AugSeptember: average high 75 °F, low 38 °F 75°38° SepOctober: average high 60 °F, low 26 °F 60°26° OctNovember: average high 46 °F, low 14 °F 46°14° NovDecember: average high 32 °F, low 0 °F 32°0° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.37 in precipitation, 8 in snowfall 0.4❄8 JanFebruary: 0.50 in precipitation, 7 in snowfall 0.5❄7 FebMarch: 0.89 in precipitation, 8.5 in snowfall 0.9❄9 MarApril: 1.85 in precipitation, 7.8 in snowfall 1.9❄8 AprMay: 2.43 in precipitation, 0.8 in snowfall 2.4❄1 MayJune: 1.34 in precipitation 1.3 JunJuly: 0.75 in precipitation 0.8 JulAugust: 0.73 in precipitation 0.7 AugSeptember: 1.23 in precipitation, 0.3 in snowfall 1.2 SepOctober: 1.34 in precipitation, 3.6 in snowfall 1.3❄4 OctNovember: 0.67 in precipitation, 6.4 in snowfall 0.7❄6 NovDecember: 0.51 in precipitation, 8.4 in snowfall 0.5❄8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Thermopolis 9ne, WY (4 mi away); precipitation: Thermopolis 9ne, WY (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

824014b
Worland, WY · 14 mi
824435a
Thermopolis, WY · 16 mi
824324b
Manderson, WY · 33 mi
826494b
Shoshoni, WY · 37 mi
824104b
Basin, WY · 38 mi
824344b
Otto, WY · 38 mi
826425a
Lysite, WY · 45 mi
824285a
Hyattville, WY · 45 mi

Wyoming planting zones →

Questions about 82430

What planting zone is ZIP code 82430?

ZIP code 82430 (Kirby, WY) 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 Kirby, WY?

The median last spring frost (32 °F) near 82430 is May 24; after June 9 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Thermopolis 9ne station.

When is the first frost in Kirby, WY?

The median first fall frost near 82430 is September 16, giving a median frost-free growing season of 112 days.

When should I plant tomatoes in 82430?

Start tomato seeds indoors around Mar 29 – Apr 12 and set transplants outside around May 31 – Jun 14, one to three weeks after the median last frost.

How much rain and snow does 82430 get?

About 12.6 inches of precipitation a year and 51 inches of snowfall (NOAA 1991–2020 normals, Thermopolis 9ne station).

How hot do summers get in Kirby, WY?

The average high peaks at 88 °F in July, with about 34 days a year at 90 °F or more.

Did spring come early in Kirby, WY in 2026?

Spring leaf-out near 82430 came on Mar 21 in 2026, 18 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Kirby, WY?

Long-day onions: the longest day near 82430 is 15 h 28 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).