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

Planting zone for 99640 — Nondalton, AK

ZIP code 99640 (Nondalton, Lake and Peninsula County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 12 and the first fall frost September 24.

Where ZIP 99640 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 frostMay 12
First frostSep 24
2012 zone4a

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 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Nondalton, 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 Nondalton, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 12median — 50% chance of a later frost
Safe for tender plantsMay 27only 10% chance of frost after
First fall frostSeptember 24median — 10% chance by Sep 8
Growing season134 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 29 and returns around October 4.

From the NOAA station Port Alsworth, AK — 56 miles away, elevation 259 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 99640

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 31 – Apr 14
SpinachSow outdoors · Mar 31 – Apr 21
Broccoli, cabbageStart indoors · Mar 3 – Mar 17
Broccoli, cabbageTransplant · Apr 21 – May 5
Onion setsPlant outdoors · Apr 14 – Apr 28
PotatoesPlant outdoors · Apr 21 – May 5
LettuceSow outdoors · Apr 14 – Apr 28
Carrots, beetsSow outdoors · Apr 21 – May 5
TomatoesStart indoors · Mar 17 – Mar 31
TomatoesTransplant · May 19 – Jun 2
Peppers, eggplantStart indoors · Mar 3 – Mar 17
Peppers, eggplantTransplant · May 26 – Jun 9
BeansSow outdoors · May 19 – Jun 2
Sweet cornSow outdoors · May 19 – Jun 2
Cucumbers, squashSow outdoors · May 19 – Jun 2
Fall lettuce, spinachSow outdoors · Jul 30 – Aug 13
GarlicPlant cloves · Sep 10 – Oct 15
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 12) and first fall frost (Sep 24) 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 Nondalton, AK.

Soil in Nondalton, AK

The soil mapped at the center of ZIP 99640 is R28-Alpine scrub colluvial mountains — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer
pH4.2strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter80%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Interior Alaska Mountains-Alpine and Boreal Low Mountains.

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 99640; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Nondalton, AK

Summer high69 °Faverage high, July
Winter low10 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights172nights a year at 32 °F or less
Growing degree days880base 50 °F — the season’s usable heat
Longest day19 h 09 mindaylight on June 21
Shortest day5 h 38 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation13.1 inper year, rain and melted snow
Snowfall88 inper year; 112 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 24 °F, low 10 °F 24°10° JanFebruary: average high 30 °F, low 15 °F 30°15° FebMarch: average high 35 °F, low 15 °F 35°15° MarApril: average high 47 °F, low 30 °F 47°30° AprMay: average high 59 °F, low 39 °F 59°39° MayJune: average high 67 °F, low 47 °F 67°47° JunJuly: average high 69 °F, low 52 °F 69°52° JulAugust: average high 66 °F, low 49 °F 66°49° AugSeptember: average high 57 °F, low 42 °F 57°42° SepOctober: average high 44 °F, low 32 °F 44°32° OctNovember: average high 32 °F, low 21 °F 32°21° NovDecember: average high 27 °F, low 15 °F 27°15° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.70 in precipitation, 13.9 in snowfall 0.7❄14 JanFebruary: 0.85 in precipitation, 13.1 in snowfall 0.8❄13 FebMarch: 0.63 in precipitation, 12.1 in snowfall 0.6❄12 MarApril: 0.50 in precipitation, 7.2 in snowfall 0.5❄7 AprMay: 0.43 in precipitation, 0.8 in snowfall 0.4❄1 MayJune: 0.73 in precipitation 0.7 JunJuly: 1.35 in precipitation 1.4 JulAugust: 1.70 in precipitation 1.7 AugSeptember: 2.57 in precipitation, 0.3 in snowfall 2.6 SepOctober: 1.32 in precipitation, 4.9 in snowfall 1.3❄5 OctNovember: 1.31 in precipitation, 17.3 in snowfall 1.3❄17 NovDecember: 0.98 in precipitation, 18.3 in snowfall 1.0❄18 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Port Alsworth, AK (56 mi away); precipitation: Port Alsworth, AK (56 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

5 of the 7 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

995573a
Aniak, AK · 53 mi
996534a
Port Alsworth, AK · 57 mi
996064b
Iliamna, AK · 72 mi
996474b
Pedro Bay, AK · 77 mi
996682b
Sleetmute, AK · 82 mi
996134a
King Salmon, AK · 114 mi
996254b
Levelock, AK · 123 mi

Alaska planting zones →

Questions about 99640

What planting zone is ZIP code 99640?

ZIP code 99640 (Nondalton, 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 Nondalton, AK?

The median last spring frost (32 °F) near 99640 is May 12; after May 27 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Port Alsworth station.

When is the first frost in Nondalton, AK?

The median first fall frost near 99640 is September 24, giving a median frost-free growing season of 134 days.

When should I plant tomatoes in 99640?

Start tomato seeds indoors around Mar 17 – Mar 31 and set transplants outside around May 19 – Jun 2, one to three weeks after the median last frost.

How much rain and snow does 99640 get?

About 13.1 inches of precipitation a year and 88 inches of snowfall (NOAA 1991–2020 normals, Port Alsworth station).

How hot do summers get in Nondalton, AK?

The average high peaks at 69 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99640 have?

The USDA soil survey maps R28-Alpine scrub colluvial mountains at the center of ZIP 99640: moderately decomposed plant material, well drained, pH about 4.2 (strongly acidic).

What kind of onions grow in Nondalton, AK?

Long-day onions: the longest day near 99640 is 19 h 09 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).