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

Planting zone for 99620 — Kotlik, AK

ZIP code 99620 (Kotlik, Kusilvak County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F.

Where ZIP 99620 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 frostrare
First frostrare
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 Kotlik, 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

No NOAA station with frost records lies within 90 miles of Kotlik, AK, so we don't show frost dates here rather than guess. Your local extension office can give you a date.

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 Kotlik, AK.

Soil in Kotlik, AK

The soil mapped at the center of ZIP 99620 is E38-maritime wet meadow-silty low coastal plains — slightly decomposed plant material, very poorly drained.

TextureSlightly decomposed plant materialtop layer
pH5.3strongly 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-Maritime Lowland-Coastal Plains, Low.

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 99620; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Kotlik, AK

Longest day20 h 20 mindaylight on June 21
Shortest day4 h 42 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

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.

995814a
Emmonak, AK · 40 mi
995544a
Alakanuk, AK · 41 mi
996713b
Stebbins, AK · 50 mi
996593b
Saint Michael, AK · 53 mi
996324a
Mountain Village, AK · 63 mi
996664a
Nunam Iqua, AK · 65 mi
996584a
Saint Marys, AK · 65 mi
996504a
Pilot Station, AK · 78 mi

Alaska planting zones →

Questions about 99620

What planting zone is ZIP code 99620?

ZIP code 99620 (Kotlik, 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).

What kind of soil does 99620 have?

The USDA soil survey maps E38-maritime wet meadow-silty low coastal plains at the center of ZIP 99620: slightly decomposed plant material, very poorly drained, pH about 5.3 (strongly acidic).

What kind of onions grow in Kotlik, AK?

Long-day onions: the longest day near 99620 is 20 h 20 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99620 change?

Yes. The 2012 USDA map put 99620 in zone 3b; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.