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

Planting zone for 99670 — South Naknek, AK

ZIP code 99670 (South Naknek, Bristol Bay County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 26 and the first fall frost September 15.

Where ZIP 99670 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.

Zone4b−25 to −20 °F
Coldest night−31.7 to −28.9 °C
Last frostMay 26
First frostSep 15
2012 zone4a

Was 4a 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 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for South Naknek, 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 South Naknek, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 26median — 50% chance of a later frost
Safe for tender plantsJune 11only 10% chance of frost after
First fall frostSeptember 15median — 10% chance by Aug 31
Growing season111 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 8 and returns around September 27.

From the NOAA station King Salmon, AK — 13 miles away, elevation 62 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 99670

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 14 – Apr 28
SpinachSow outdoors · Apr 14 – May 5
Broccoli, cabbageStart indoors · Mar 17 – Mar 31
Broccoli, cabbageTransplant · May 5 – May 19
Onion setsPlant outdoors · Apr 28 – May 12
PotatoesPlant outdoors · May 5 – May 19
LettuceSow outdoors · Apr 28 – May 12
Carrots, beetsSow outdoors · May 5 – May 19
TomatoesStart indoors · Mar 31 – Apr 14
TomatoesTransplant · Jun 2 – Jun 16
Peppers, eggplantStart indoors · Mar 17 – Mar 31
Peppers, eggplantTransplant · Jun 9 – Jun 23
BeansSow outdoors · Jun 2 – Jun 16
Sweet cornSow outdoors · Jun 2 – Jun 16
Cucumbers, squashSow outdoors · Jun 2 – Jun 16
Fall lettuce, spinachSow outdoors · Jul 21 – Aug 4
GarlicPlant cloves · Sep 1 – Oct 6
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 26) and first fall frost (Sep 15) 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 4b in Alaska

260 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 11

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 °FPacific silver fir165 ft · blooms late spring · low shade tolerance · to −28 °Fpaper birch70 ft · blooms mid spring · high shade tolerance · to −62 °Fquaking aspen65 ft · blooms mid spring · high shade tolerance · to −70 °F

Shrubs 44

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °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 °F

Wildflowers & perennials 112

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine aster0.3 ft · blooms early summer · medium shade tolerance · to −28 °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 alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °F

Grasses 84

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 South Naknek, AK.

Soil in South Naknek, AK

The soil mapped at the center of ZIP 99670 is E36-maritime scrub-ashy till slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH4.4strongly 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: Bristol Bay-Northern Alaska Peninsula Lowlands-Maritime Upland-Glaciated Plains, 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 99670; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in South Naknek, AK

Summer high65 °Faverage high, July
Winter low10 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights192nights a year at 32 °F or less
Growing degree days566base 50 °F — the season’s usable heat
Longest day18 h 24 mindaylight on June 21
Shortest day6 h 16 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation21.4 inper year, rain and melted snow
Snowfall47 inper year; 84 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 32 °F, low 15 °F 32°15° MarApril: average high 45 °F, low 28 °F 45°28° AprMay: average high 55 °F, low 36 °F 55°36° MayJune: average high 62 °F, low 44 °F 62°44° JunJuly: average high 65 °F, low 49 °F 65°49° JulAugust: average high 63 °F, low 48 °F 63°48° AugSeptember: average high 56 °F, low 41 °F 56°41° SepOctober: average high 44 °F, low 29 °F 44°29° OctNovember: average high 32 °F, low 18 °F 32°18° NovDecember: average high 26 °F, low 11 °F 26°11° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″January: 0.93 in precipitation, 8.6 in snowfall 0.9❄9 JanFebruary: 0.91 in precipitation, 7.2 in snowfall 0.9❄7 FebMarch: 0.76 in precipitation, 7.2 in snowfall 0.8❄7 MarApril: 1.04 in precipitation, 4.4 in snowfall 1.0❄4 AprMay: 1.44 in precipitation, 0.6 in snowfall 1.4❄1 MayJune: 1.83 in precipitation 1.8 JunJuly: 2.46 in precipitation 2.5 JulAugust: 3.26 in precipitation 3.3 AugSeptember: 3.40 in precipitation 3.4 SepOctober: 2.31 in precipitation, 2.5 in snowfall 2.3❄3 OctNovember: 1.72 in precipitation, 6.7 in snowfall 1.7❄7 NovDecember: 1.38 in precipitation, 10.2 in snowfall 1.4❄10 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: King Salmon, AK (13 mi away); precipitation: King Salmon, AK (13 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

996334b
Naknek, AK · 10 mi
996254b
Levelock, AK · 28 mi
995795a
Egegik, AK · 35 mi
995804b
Ekwok, AK · 50 mi
996364b
New Stuyahok, AK · 58 mi
996134a
King Salmon, AK · 64 mi
996495a
Pilot Point, AK · 81 mi

Alaska planting zones →

Questions about 99670

What planting zone is ZIP code 99670?

ZIP code 99670 (South Naknek, AK) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in South Naknek, AK?

The median last spring frost (32 °F) near 99670 is May 26; after June 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, King Salmon station.

When is the first frost in South Naknek, AK?

The median first fall frost near 99670 is September 15, giving a median frost-free growing season of 111 days.

When should I plant tomatoes in 99670?

Start tomato seeds indoors around Mar 31 – Apr 14 and set transplants outside around Jun 2 – Jun 16, one to three weeks after the median last frost.

How much rain and snow does 99670 get?

About 21.4 inches of precipitation a year and 47 inches of snowfall (NOAA 1991–2020 normals, King Salmon station).

How hot do summers get in South Naknek, AK?

The average high peaks at 65 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99670 have?

The USDA soil survey maps E36-maritime scrub-ashy till slopes at the center of ZIP 99670: slightly decomposed plant material, well drained, pH about 4.4 (strongly acidic).

What kind of onions grow in South Naknek, AK?

Long-day onions: the longest day near 99670 is 18 h 24 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99670 change?

Yes. The 2012 USDA map put 99670 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.