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

Planting zone for 99754 — Koyukuk, AK

ZIP code 99754 (Koyukuk, Yukon-Koyukuk (CA) County) is in USDA zone 2a: the coldest winter night averages −50 to −45 °F. The median last spring frost is May 18 and the first fall frost September 8.

Where ZIP 99754 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.

Zone2a−50 to −45 °F

Coldest night−45.6 to −42.8 °C

Last frostMay 18

First frostSep 8

2012 zone1b

Was 1b 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 2a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Koyukuk, 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 Koyukuk, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 18median — 50% chance of a later frost

Safe for tender plantsJune 1only 10% chance of frost after

First fall frostSeptember 8median — 10% chance by Aug 24

Growing season111 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 10 and returns around September 18.

From the NOAA station Galena, AK — 27 miles away, elevation 151 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 99754

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 6 – Apr 20

SpinachSow outdoors · Apr 6 – Apr 27

Broccoli, cabbageStart indoors · Mar 9 – Mar 23

Broccoli, cabbageTransplant · Apr 27 – May 11

Onion setsPlant outdoors · Apr 20 – May 4

PotatoesPlant outdoors · Apr 27 – May 11

LettuceSow outdoors · Apr 20 – May 4

Carrots, beetsSow outdoors · Apr 27 – May 11

TomatoesStart indoors · Mar 23 – Apr 6

TomatoesTransplant · May 25 – Jun 8

Peppers, eggplantStart indoors · Mar 9 – Mar 23

Peppers, eggplantTransplant · Jun 1 – Jun 15

BeansSow outdoors · May 25 – Jun 8

Sweet cornSow outdoors · May 25 – Jun 8

Cucumbers, squashSow outdoors · May 25 – Jun 8

Fall lettuce, spinachSow outdoors · Jul 14 – Jul 28

GarlicPlant cloves · Aug 25 – Sep 29

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 18) and first fall frost (Sep 8) 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 2a in Alaska

44 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −50 °F or colder — the bottom of zone 2a. 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 Koyukuk, AK.

Soil in Koyukuk, AK

The soil mapped at the center of ZIP 99754 is E30-boreal taiga-silty frozen loess 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: Yukon-Kuskokwim Highlands-Boreal Upland-Plains and Hills.

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 99754; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Koyukuk, AK

Summer high69 °Faverage high, June

Winter low−17 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights230nights a year at 32 °F or less

Growing degree days769base 50 °F — the season’s usable heat

Longest day21 h 55 mindaylight on June 21

Shortest day3 h 39 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation13.9 inper year, rain and melted snow

Snowfall77 inper year; 193 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: Galena, AK (27 mi away); precipitation: Galena, AK (27 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Alaska planting zones →

Questions about 99754

What planting zone is ZIP code 99754?

ZIP code 99754 (Koyukuk, AK) is in USDA hardiness zone 2a on the 2023 map: the coldest night of an average winter reaches −50 to −45 °F (−45.6 to −42.8 °C).

When is the last frost in Koyukuk, AK?

The median last spring frost (32 °F) near 99754 is May 18; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Galena station.

When is the first frost in Koyukuk, AK?

The median first fall frost near 99754 is September 8, giving a median frost-free growing season of 111 days.

When should I plant tomatoes in 99754?

Start tomato seeds indoors around Mar 23 – Apr 6 and set transplants outside around May 25 – Jun 8, one to three weeks after the median last frost.

How much rain and snow does 99754 get?

About 13.9 inches of precipitation a year and 77 inches of snowfall (NOAA 1991–2020 normals, Galena station).

How hot do summers get in Koyukuk, AK?

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

What kind of soil does 99754 have?

The USDA soil survey maps E30-boreal taiga-silty frozen loess slopes at the center of ZIP 99754: peat, poorly drained.

What kind of onions grow in Koyukuk, AK?

Long-day onions: the longest day near 99754 is 21 h 55 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99754 change?

Yes. The 2012 USDA map put 99754 in zone 1b; the 2023 map puts it in zone 2a. The newer map uses 1991–2020 data and more weather stations.