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

Planting zone for 82644 — Mills, WY

ZIP code 82644 (Mills, Natrona County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 10 and the first fall frost September 29.

Where ZIP 82644 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 10
First frostSep 29
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 Mills, 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 Mills, WY

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 10median — 50% chance of a later frost
Safe for tender plantsMay 24only 10% chance of frost after
First fall frostSeptember 29median — 10% chance by Sep 14
Growing season138 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 1 and returns around October 6.

From the NOAA station Casper Wwtp, WY — 4 miles away, elevation 5,099 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 82644

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 29 – Apr 12
SpinachSow outdoors · Mar 29 – Apr 19
Broccoli, cabbageStart indoors · Mar 1 – Mar 15
Broccoli, cabbageTransplant · Apr 19 – May 3
Onion setsPlant outdoors · Apr 12 – Apr 26
PotatoesPlant outdoors · Apr 19 – May 3
LettuceSow outdoors · Apr 12 – Apr 26
Carrots, beetsSow outdoors · Apr 19 – May 3
TomatoesStart indoors · Mar 15 – Mar 29
TomatoesTransplant · May 17 – May 31
Peppers, eggplantStart indoors · Mar 1 – Mar 15
Peppers, eggplantTransplant · May 24 – Jun 7
BeansSow outdoors · May 17 – May 31
Sweet cornSow outdoors · May 17 – May 31
Cucumbers, squashSow outdoors · May 17 – May 31
Fall lettuce, spinachSow outdoors · Aug 4 – Aug 18
GarlicPlant cloves · Sep 15 – Oct 20
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 10) and first fall frost (Sep 29) 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 82644 came on Mar 1 — 38 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 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.

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 98

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 249

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 161

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 Mills, WY.

Soil in Mills, WY

The soil mapped at the center of ZIP 82644 is Samday — very cobbly clay, well drained.

TextureVery cobbly clayholds water and nutrients; slow to drain and warm up
pH8.5alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Samday very cobbly clay, 20 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 82644; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mills, WY

Summer high88 °Faverage high, July
Winter low17 °Faverage low, January
Hot days36days a year at 90 °F or more
Freezing nights163nights a year at 32 °F or less
Growing degree days2,405base 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)
Precipitation16.2 inper year, rain and melted snow
Snowfall82 inper year; 84 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 38 °F, low 17 °F 38°17° JanFebruary: average high 40 °F, low 18 °F 40°18° FebMarch: average high 49 °F, low 25 °F 49°25° MarApril: average high 57 °F, low 31 °F 57°31° AprMay: average high 67 °F, low 41 °F 67°41° MayJune: average high 79 °F, low 50 °F 79°50° JunJuly: average high 88 °F, low 56 °F 88°56° JulAugust: average high 87 °F, low 55 °F 87°55° AugSeptember: average high 76 °F, low 44 °F 76°44° SepOctober: average high 61 °F, low 33 °F 61°33° OctNovember: average high 48 °F, low 25 °F 48°25° NovDecember: average high 38 °F, low 17 °F 38°17° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.76 in precipitation, 11.1 in snowfall 0.8❄11 JanFebruary: 0.89 in precipitation, 14.6 in snowfall 0.9❄15 FebMarch: 1.78 in precipitation, 12.3 in snowfall 1.8❄12 MarApril: 2.04 in precipitation, 10.7 in snowfall 2.0❄11 AprMay: 2.64 in precipitation, 3 in snowfall 2.6❄3 MayJune: 1.82 in precipitation 1.8 JunJuly: 1.00 in precipitation 1.0 JulAugust: 1.03 in precipitation 1.0 AugSeptember: 1.13 in precipitation, 0.4 in snowfall 1.1 SepOctober: 1.39 in precipitation, 5.9 in snowfall 1.4❄6 OctNovember: 0.76 in precipitation, 6.7 in snowfall 0.8❄7 NovDecember: 0.92 in precipitation, 17 in snowfall 0.9❄17 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Casper Wwtp, WY (4 mi away); precipitation: Casper 4.3 Wsw, WY (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

826025a
Casper, WY · 3 mi
826055a
Casper, WY · 3 mi
826095a
Casper, WY · 11 mi
826365a
Evansville, WY · 11 mi
826015a
Casper, WY · 16 mi
826045a
Casper, WY · 18 mi
826465a
Natrona, WY · 22 mi
826375a
Glenrock, WY · 27 mi

Wyoming planting zones →

Questions about 82644

What planting zone is ZIP code 82644?

ZIP code 82644 (Mills, 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 Mills, WY?

The median last spring frost (32 °F) near 82644 is May 10; after May 24 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Casper Wwtp station.

When is the first frost in Mills, WY?

The median first fall frost near 82644 is September 29, giving a median frost-free growing season of 138 days.

When should I plant tomatoes in 82644?

Start tomato seeds indoors around Mar 15 – Mar 29 and set transplants outside around May 17 – May 31, one to three weeks after the median last frost.

How much rain and snow does 82644 get?

About 16.2 inches of precipitation a year and 82 inches of snowfall (NOAA 1991–2020 normals, Casper 4.3 Wsw station).

How hot do summers get in Mills, WY?

The average high peaks at 88 °F in July, with about 36 days a year at 90 °F or more.

What kind of soil does 82644 have?

The USDA soil survey maps Samday at the center of ZIP 82644: very cobbly clay, well drained, pH about 8.5 (alkaline).

Did spring come early in Mills, WY in 2026?

Spring leaf-out near 82644 came on Mar 1 in 2026, 38 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mills, WY?

Long-day onions: the longest day near 82644 is 15 h 21 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).