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

Planting zone for 99623 — Wasilla, AK

ZIP code 99623 (Wasilla, Matanuska-Susitna Borough) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 9 and the first fall frost September 26.

Where ZIP 99623 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 9
First frostSep 26
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 Wasilla, AK…

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 Wasilla, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 9median — 50% chance of a later frost
Safe for tender plantsMay 22only 10% chance of frost after
First fall frostSeptember 26median — 10% chance by Sep 12
Growing season139 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 26 and returns around October 7.

From the NOAA station Eagle Rvr Gakona Circle, AK — 15 miles away, elevation 568 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 99623

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 28 – Apr 11
SpinachSow outdoors · Mar 28 – Apr 18
Broccoli, cabbageStart indoors · Feb 28 – Mar 14
Broccoli, cabbageTransplant · Apr 18 – May 2
Onion setsPlant outdoors · Apr 11 – Apr 25
PotatoesPlant outdoors · Apr 18 – May 2
LettuceSow outdoors · Apr 11 – Apr 25
Carrots, beetsSow outdoors · Apr 18 – May 2
TomatoesStart indoors · Mar 14 – Mar 28
TomatoesTransplant · May 16 – May 30
Peppers, eggplantStart indoors · Feb 28 – Mar 14
Peppers, eggplantTransplant · May 23 – Jun 6
BeansSow outdoors · May 16 – May 30
Sweet cornSow outdoors · May 16 – May 30
Cucumbers, squashSow outdoors · May 16 – May 30
Fall lettuce, spinachSow outdoors · Aug 1 – Aug 15
GarlicPlant cloves · Sep 12 – Oct 17
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Sep 26) 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.

Native plants for zone 4b in Alaska

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

Trees 11

balsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack spruce65 ft · blooms late spring · low shade tolerance · to −79 °Flodgepole pine99 ft · blooms mid summer · high shade tolerance · to −70 °FPacific silver fir165 ft · blooms late spring · low shade tolerance · to −28 °Fpaper birch70 ft · blooms mid spring · high shade tolerance · to −62 °Fquaking aspen65 ft · blooms mid spring · high shade tolerance · to −70 °F

Shrubs 44

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FBarclay's willow15 ft · high shade tolerance · to −43 °Fblack crowberry1 ft · blooms mid summer · high shade tolerance · to −43 °Fblack hawthorn15 ft · blooms mid spring · medium shade tolerance · to −47 °Fbog blueberry2 ft · blooms early summer · medium shade tolerance · to −38 °F

Wildflowers & perennials 112

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine aster0.3 ft · blooms early summer · medium shade tolerance · to −28 °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 °F

Grasses 84

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °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 °Farctic bluegrass2 ft · high shade tolerance · to −62 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °Fbeaked sedge4 ft · blooms late spring · low 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 Wasilla, AK.

Soil in Wasilla, AK

The soil mapped at the center of ZIP 99623 is Estelle — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH3.9strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter85%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Estelle silt loam, rolling.

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 99623; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Wasilla, AK

Summer high67 °Faverage high, July
Winter low9 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights191nights a year at 32 °F or less
Growing degree days662base 50 °F — the season’s usable heat
Longest day19 h 29 mindaylight on June 21
Shortest day5 h 22 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation17.7 inper year, rain and melted snow
Snowfall71 inper year; 158 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 20 °F, low 9 °F 20°9° JanFebruary: average high 27 °F, low 13 °F 27°13° FebMarch: average high 33 °F, low 16 °F 33°16° MarApril: average high 46 °F, low 29 °F 46°29° AprMay: average high 58 °F, low 38 °F 58°38° MayJune: average high 64 °F, low 46 °F 64°46° JunJuly: average high 67 °F, low 50 °F 67°50° JulAugust: average high 63 °F, low 48 °F 63°48° AugSeptember: average high 54 °F, low 40 °F 54°40° SepOctober: average high 40 °F, low 28 °F 40°28° OctNovember: average high 26 °F, low 16 °F 26°16° NovDecember: average high 22 °F, low 12 °F 22°12° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.97 in precipitation, 12.5 in snowfall 1.0❄13 JanFebruary: 1.13 in precipitation, 11.7 in snowfall 1.1❄12 FebMarch: 0.85 in precipitation, 8.9 in snowfall 0.8❄9 MarApril: 0.55 in precipitation, 4.5 in snowfall 0.6❄5 AprMay: 0.90 in precipitation, 0.4 in snowfall 0.9 MayJune: 1.14 in precipitation 1.1 JunJuly: 2.09 in precipitation 2.1 JulAugust: 2.82 in precipitation 2.8 AugSeptember: 2.67 in precipitation, 0.4 in snowfall 2.7 SepOctober: 1.74 in precipitation, 3.5 in snowfall 1.7❄4 OctNovember: 1.58 in precipitation, 12.3 in snowfall 1.6❄12 NovDecember: 1.23 in precipitation, 16.3 in snowfall 1.2❄16 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Eagle Rvr Gakona Circle, AK (15 mi away); precipitation: Eagle Rvr Gakona Circle, AK (15 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

996524a
Big Lake, AK · 6 mi
995065a
Jber, AK · 12 mi
996944a
Houston, AK · 13 mi
995055a
Jber, AK · 14 mi
995095a
Anchorage, AK · 15 mi
995145a
Anchorage, AK · 15 mi
995205b
Anchorage, AK · 15 mi
995215a
Anchorage, AK · 15 mi

All 4 ZIP codes in Wasilla → · Alaska planting zones →

Questions about 99623

What planting zone is ZIP code 99623?

ZIP code 99623 (Wasilla, AK) 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 Wasilla, AK?

The median last spring frost (32 °F) near 99623 is May 9; after May 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Eagle Rvr Gakona Circle station.

When is the first frost in Wasilla, AK?

The median first fall frost near 99623 is September 26, giving a median frost-free growing season of 139 days.

When should I plant tomatoes in 99623?

Start tomato seeds indoors around Mar 14 – Mar 28 and set transplants outside around May 16 – May 30, one to three weeks after the median last frost.

How much rain and snow does 99623 get?

About 17.7 inches of precipitation a year and 71 inches of snowfall (NOAA 1991–2020 normals, Eagle Rvr Gakona Circle station).

How hot do summers get in Wasilla, AK?

The average high peaks at 67 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99623 have?

The USDA soil survey maps Estelle at the center of ZIP 99623: slightly decomposed plant material, well drained, pH about 3.9 (strongly acidic).

What kind of onions grow in Wasilla, AK?

Long-day onions: the longest day near 99623 is 19 h 29 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).