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

Planting zone for 99634 — Napakiak, AK

ZIP code 99634 (Napakiak, Bethel Census Area County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 21 and the first fall frost September 22.

Where ZIP 99634 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 21

First frostSep 22

2012 zone3b

Was 3b on the 2012 map — half a 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 Napakiak, 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 Napakiak, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 21median — 50% chance of a later frost

Safe for tender plantsJune 2only 10% chance of frost after

First fall frostSeptember 22median — 10% chance by Sep 7

Growing season122 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 11 and returns around October 1.

From the NOAA station Bethel Airport, AK — 9 miles away, elevation 102 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 99634

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 9 – Apr 23

SpinachSow outdoors · Apr 9 – Apr 30

Broccoli, cabbageStart indoors · Mar 12 – Mar 26

Broccoli, cabbageTransplant · Apr 30 – May 14

Onion setsPlant outdoors · Apr 23 – May 7

PotatoesPlant outdoors · Apr 30 – May 14

LettuceSow outdoors · Apr 23 – May 7

Carrots, beetsSow outdoors · Apr 30 – May 14

TomatoesStart indoors · Mar 26 – Apr 9

TomatoesTransplant · May 28 – Jun 11

Peppers, eggplantStart indoors · Mar 12 – Mar 26

Peppers, eggplantTransplant · Jun 4 – Jun 18

BeansSow outdoors · May 28 – Jun 11

Sweet cornSow outdoors · May 28 – Jun 11

Cucumbers, squashSow outdoors · May 28 – Jun 11

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 21) 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.

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.

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 Napakiak, AK.

Soil in Napakiak, AK

The soil mapped at the center of ZIP 99634 is E38-maritime wet meadow-organic depressions — peat, very poorly drained.

TexturePeattop layer

pH6.0slightly acidic; most vegetables like 6.0–7.0

DrainageVery poorly drainedconsider raised beds

Organic matter80%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classNot prime farmlandUSDA classification

Map unit: Yukon-Kuskokwim Coastal Plain-Boreal Lowland-Flood Plains and Terraces.

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 99634; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Napakiak, AK

Summer high64 °Faverage high, July

Winter low1 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights214nights a year at 32 °F or less

Growing degree days501base 50 °F — the season’s usable heat

Longest day19 h 08 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)

Precipitation19.7 inper year, rain and melted snow

Snowfall64 inper year; 153 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Bethel Airport, AK (9 mi away); precipitation: Bethel Airport, AK (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

995594a

Bethel, AK · 8 mi

996414a

Nunapitchuk, AK · 20 mi

Tuntutuliak, AK · 32 mi

995784a

Eek, AK · 32 mi

Alaska planting zones →

Questions about 99634

What planting zone is ZIP code 99634?

ZIP code 99634 (Napakiak, 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 Napakiak, AK?

The median last spring frost (32 °F) near 99634 is May 21; after June 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Bethel Airport station.

When is the first frost in Napakiak, AK?

The median first fall frost near 99634 is September 22, giving a median frost-free growing season of 122 days.

When should I plant tomatoes in 99634?

Start tomato seeds indoors around Mar 26 – Apr 9 and set transplants outside around May 28 – Jun 11, one to three weeks after the median last frost.

How much rain and snow does 99634 get?

About 19.7 inches of precipitation a year and 64 inches of snowfall (NOAA 1991–2020 normals, Bethel Airport station).

How hot do summers get in Napakiak, AK?

The average high peaks at 64 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99634 have?

The USDA soil survey maps E38-maritime wet meadow-organic depressions at the center of ZIP 99634: peat, very poorly drained, pH about 6.0 (slightly acidic).

What kind of onions grow in Napakiak, AK?

Long-day onions: the longest day near 99634 is 19 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99634 change?

Yes. The 2012 USDA map put 99634 in zone 3b; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.