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

Planting zone for 99607 — Kalskag, AK

ZIP code 99607 (Kalskag, Bethel Census Area County) is in USDA zone 3b: the coldest winter night averages −35 to −30 °F. The median last spring frost is May 21 and the first fall frost September 22.

Where ZIP 99607 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.

Zone3b−35 to −30 °F
Coldest night−37.2 to −34.4 °C
Last frostMay 21
First frostSep 22
2012 zone2b

Was 2b on the 2012 map — a full zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 3b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Kalskag, 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 Kalskag, 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 — 71 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 99607

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 3b in Alaska

172 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −35 °F or colder — the bottom of zone 3b. Each links to its USDA PLANTS profile.

Trees 8

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 °Fsubalpine fir90 ft · blooms late spring · low shade tolerance · to −51 °F

Shrubs 32

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 °Fchokecherry25 ft · blooms mid spring · high shade tolerance · to −43 °F

Wildflowers & perennials 64

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 61

alpine 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 °Fbearded fescue1.2 ft · blooms late spring · low shade tolerance · to −38 °FBebb's sedge3 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 Kalskag, AK.

Soil in Kalskag, AK

The soil mapped at the center of ZIP 99607 is 38-Ulesqiirluni — moderately decomposed plant material, moderately well drained.

TextureModerately decomposed plant materialtop layer
pH6.3slightly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter75%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Ulesqiirluni-Uknavikfamily complex, 0 to 3 percent slopes.

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 99607; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Kalskag, 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 31 mindaylight on June 21
Shortest day5 h 20 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Average high and low, by month

−10°0°10°20°30°40°50°60°70°32 °FJanuary: average high 13 °F, low 1 °F 13°1° JanFebruary: average high 20 °F, low 7 °F 20°7° FebMarch: average high 22 °F, low 7 °F 22°7° MarApril: average high 37 °F, low 21 °F 37°21° AprMay: average high 52 °F, low 34 °F 52°34° MayJune: average high 62 °F, low 45 °F 62°45° JunJuly: average high 64 °F, low 49 °F 64°49° JulAugust: average high 61 °F, low 47 °F 61°47° AugSeptember: average high 53 °F, low 39 °F 53°39° SepOctober: average high 38 °F, low 26 °F 38°26° OctNovember: average high 24 °F, low 13 °F 24°13° NovDecember: average high 16 °F, low 4 °F 16°4° Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Bethel Airport, AK (71 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.

996263b
Lower Kalskag, AK · 2 mi
996793b
Tuluksak, AK · 36 mi
996573b
Russian Mission, AK · 42 mi
996023a
Holy Cross, AK · 47 mi
995523b
Akiak, AK · 52 mi
995513b
Akiachak, AK · 55 mi
996214a
Kwethluk, AK · 63 mi
995583b
Anvik, AK · 76 mi

Alaska planting zones →

Questions about 99607

What planting zone is ZIP code 99607?

ZIP code 99607 (Kalskag, AK) is in USDA hardiness zone 3b on the 2023 map: the coldest night of an average winter reaches −35 to −30 °F (−37.2 to −34.4 °C).

When is the last frost in Kalskag, AK?

The median last spring frost (32 °F) near 99607 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 Kalskag, AK?

The median first fall frost near 99607 is September 22, giving a median frost-free growing season of 122 days.

When should I plant tomatoes in 99607?

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 hot do summers get in Kalskag, 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 99607 have?

The USDA soil survey maps 38-Ulesqiirluni at the center of ZIP 99607: moderately decomposed plant material, moderately well drained, pH about 6.3 (slightly acidic).

What kind of onions grow in Kalskag, AK?

Long-day onions: the longest day near 99607 is 19 h 31 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99607 change?

Yes. The 2012 USDA map put 99607 in zone 2b; the 2023 map puts it in zone 3b. The newer map uses 1991–2020 data and more weather stations.