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

Planting zone for 82604 — Casper, WY

ZIP code 82604 (Casper, Natrona County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 26 and the first fall frost September 22.

Where ZIP 82604 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostMay 26

First frostSep 22

2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Casper, 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 Casper, WY

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 26median — 50% chance of a later frost

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

First fall frostSeptember 22median — 10% chance by Sep 5

Growing season117 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around October 2.

From the NOAA station Casper Natrona Co. Airport, WY — 12 miles away, elevation 5,338 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 82604

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 14 – Apr 28

SpinachSow outdoors · Apr 14 – May 5

Broccoli, cabbageStart indoors · Mar 17 – Mar 31

Broccoli, cabbageTransplant · May 5 – May 19

Onion setsPlant outdoors · Apr 28 – May 12

PotatoesPlant outdoors · May 5 – May 19

LettuceSow outdoors · Apr 28 – May 12

Carrots, beetsSow outdoors · May 5 – May 19

TomatoesStart indoors · Mar 31 – Apr 14

TomatoesTransplant · Jun 2 – Jun 16

Peppers, eggplantStart indoors · Mar 17 – Mar 31

Peppers, eggplantTransplant · Jun 9 – Jun 23

BeansSow outdoors · Jun 2 – Jun 16

Sweet cornSow outdoors · Jun 2 – Jun 16

Cucumbers, squashSow outdoors · Jun 2 – Jun 16

Fall lettuce, spinachSow outdoors · Jul 28 – Aug 11

GarlicPlant cloves · Sep 8 – Oct 13

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 26) and first fall frost (Sep 22) 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 82604 came on Mar 18 — 26 days earlier than the 1991–2020 average (Apr 13).

average
Apr 132026
Mar 18

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 5a in Wyoming

542 plants native to the lower 48 states, recorded in Wyoming, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Casper, WY.

Soil in Casper, WY

The soil mapped at the center of ZIP 82604 is Cushman — very fine sandy loam, well drained.

TextureVery fine sandy loamdrains and warms fast; dries out and needs more feeding

pH7.2neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.5%low — add compost

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Cushman-Forkwood complex, 3 to 15 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 82604; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Casper, WY

Summer high89 °Faverage high, July

Winter low15 °Faverage low, January

Hot days38days a year at 90 °F or more

Freezing nights183nights a year at 32 °F or less

Growing degree days2,156base 50 °F — the season’s usable heat

Longest day15 h 21 mindaylight on June 21

Shortest day9 h 01 mindaylight on December 21

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

Precipitation16.6 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: Casper Natrona Co. Airport, WY (12 mi away); precipitation: Casper 10.9 Wsw, WY (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

826465a

Natrona, WY · 5 mi

826485a

Powder River, WY · 16 mi

Evansville, WY · 28 mi

All 5 ZIP codes in Casper → · Wyoming planting zones →

Questions about 82604

What planting zone is ZIP code 82604?

ZIP code 82604 (Casper, WY) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Casper, WY?

The median last spring frost (32 °F) near 82604 is May 26; after June 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Casper Natrona Co. Airport station.

When is the first frost in Casper, WY?

The median first fall frost near 82604 is September 22, giving a median frost-free growing season of 117 days.

When should I plant tomatoes in 82604?

Start tomato seeds indoors around Mar 31 – Apr 14 and set transplants outside around Jun 2 – Jun 16, one to three weeks after the median last frost.

How much rain and snow does 82604 get?

About 16.6 inches of precipitation a year (NOAA 1991–2020 normals, Casper 10.9 Wsw station).

How hot do summers get in Casper, WY?

The average high peaks at 89 °F in July, with about 38 days a year at 90 °F or more.

What kind of soil does 82604 have?

The USDA soil survey maps Cushman at the center of ZIP 82604: very fine sandy loam, well drained, pH about 7.2 (neutral).

Did spring come early in Casper, WY in 2026?

Spring leaf-out near 82604 came on Mar 18 in 2026, 26 days earlier than the 1991–2020 average (Apr 13), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Casper, WY?

Long-day onions: the longest day near 82604 is 15 h 21 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).