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

Planting zone for 99653 — Port Alsworth, AK

ZIP code 99653 (Port Alsworth, Lake and Peninsula County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is June 2 and the first fall frost September 12.

Where ZIP 99653 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.

Zone4a−30 to −25 °F
Coldest night−34.4 to −31.7 °C
Last frostJun 2
First frostSep 12
2012 zone3a

Was 3a 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 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Port Alsworth, 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 Port Alsworth, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJune 2median — 50% chance of a later frost
Safe for tender plantsJune 13only 10% chance of frost after
First fall frostSeptember 12median — 10% chance by Aug 29
Growing season101 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 19 and returns around September 25.

From the NOAA station Port Alsworth 1 Sw, AK — 2 miles away, elevation 322 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 99653

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 21 – May 5
SpinachSow outdoors · Apr 21 – May 12
Broccoli, cabbageStart indoors · Mar 24 – Apr 7
Broccoli, cabbageTransplant · May 12 – May 26
Onion setsPlant outdoors · May 5 – May 19
PotatoesPlant outdoors · May 12 – May 26
LettuceSow outdoors · May 5 – May 19
Carrots, beetsSow outdoors · May 12 – May 26
TomatoesStart indoors · Apr 7 – Apr 21
TomatoesTransplant · Jun 9 – Jun 23
Peppers, eggplantStart indoors · Mar 24 – Apr 7
Peppers, eggplantTransplant · Jun 16 – Jun 30
BeansSow outdoors · Jun 9 – Jun 23
Sweet cornSow outdoors · Jun 9 – Jun 23
Cucumbers, squashSow outdoors · Jun 9 – Jun 23
Fall lettuce, spinachSow outdoors · Jul 18 – Aug 1
GarlicPlant cloves · Aug 29 – Oct 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 2) and first fall frost (Sep 12) 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 4a in Alaska

240 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −30 °F or colder — the bottom of zone 4a. Each links to its USDA PLANTS profile.

Trees 10

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 °Fpaper birch70 ft · blooms mid spring · high shade tolerance · to −62 °Fquaking aspen65 ft · blooms mid spring · high shade tolerance · to −70 °FSitka spruce200 ft · blooms late spring · low shade tolerance · to −33 °F

Shrubs 42

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °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 °Fbog Labrador tea3 ft · blooms late spring · medium shade tolerance · to −33 °F

Wildflowers & perennials 102

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 speedwell0.8 ft · blooms mid summer · low shade tolerance · to −38 °FAmerican vetch1.3 ft · blooms late spring · high shade tolerance · to −38 °F

Grasses 78

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 Port Alsworth, AK.

Soil in Port Alsworth, AK

The soil mapped at the center of ZIP 99653 is E28-boreal taiga-silty frozen till slopes — peat, poorly drained.

TexturePeattop layer
DrainagePoorly drainedconsider raised beds
Organic matter75%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Interior Alaska Mountains-Boreal Upland and Subalpine-Mountain Valleys, Ash Influenced.

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 99653; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Port Alsworth, AK

Summer high67 °Faverage high, July
Winter low5 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights209nights a year at 32 °F or less
Growing degree days497base 50 °F — the season’s usable heat
Longest day18 h 56 mindaylight on June 21
Shortest day5 h 49 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation23.6 inper year, rain and melted snow

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 24 °F, low 5 °F 24°5° JanFebruary: average high 29 °F, low 10 °F 29°10° FebMarch: average high 32 °F, low 11 °F 32°11° MarApril: average high 46 °F, low 24 °F 46°24° AprMay: average high 58 °F, low 32 °F 58°32° MayJune: average high 65 °F, low 41 °F 65°41° JunJuly: average high 67 °F, low 46 °F 67°46° JulAugust: average high 63 °F, low 45 °F 63°45° AugSeptember: average high 55 °F, low 38 °F 55°38° SepOctober: average high 42 °F, low 25 °F 42°25° OctNovember: average high 30 °F, low 15 °F 30°15° NovDecember: average high 25 °F, low 9 °F 25°9° Dec

Precipitation by month inches

0″1″2″3″4″January: 1.55 in precipitation 1.6 JanFebruary: 1.48 in precipitation 1.5 FebMarch: 1.17 in precipitation 1.2 MarApril: 0.91 in precipitation 0.9 AprMay: 0.84 in precipitation 0.8 MayJune: 1.24 in precipitation 1.2 JunJuly: 2.15 in precipitation 2.1 JulAugust: 3.32 in precipitation 3.3 AugSeptember: 3.48 in precipitation 3.5 SepOctober: 2.25 in precipitation 2.3 OctNovember: 3.03 in precipitation 3.0 NovDecember: 2.17 in precipitation 2.2 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Port Alsworth 1 Sw, AK (2 mi away); precipitation: Port Alsworth 1 Sw, AK (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

4 of the 6 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996474b
Pedro Bay, AK · 21 mi
996064b
Iliamna, AK · 35 mi
996404a
Nondalton, AK · 57 mi
996354b
Nikiski, AK · 78 mi
996134a
King Salmon, AK · 83 mi
995573a
Aniak, AK · 95 mi

Alaska planting zones →

Questions about 99653

What planting zone is ZIP code 99653?

ZIP code 99653 (Port Alsworth, AK) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Port Alsworth, AK?

The median last spring frost (32 °F) near 99653 is June 2; after June 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Port Alsworth 1 Sw station.

When is the first frost in Port Alsworth, AK?

The median first fall frost near 99653 is September 12, giving a median frost-free growing season of 101 days.

When should I plant tomatoes in 99653?

Start tomato seeds indoors around Apr 7 – Apr 21 and set transplants outside around Jun 9 – Jun 23, one to three weeks after the median last frost.

How much rain and snow does 99653 get?

About 23.6 inches of precipitation a year (NOAA 1991–2020 normals, Port Alsworth 1 Sw station).

How hot do summers get in Port Alsworth, 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 99653 have?

The USDA soil survey maps E28-boreal taiga-silty frozen till slopes at the center of ZIP 99653: peat, poorly drained.

What kind of onions grow in Port Alsworth, AK?

Long-day onions: the longest day near 99653 is 18 h 56 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99653 change?

Yes. The 2012 USDA map put 99653 in zone 3a; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.