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

Planting zone for 99635 — Nikiski, AK

ZIP code 99635 (Nikiski, Kenai Peninsula County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 7 and the first fall frost October 7.

Where ZIP 99635 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 7
First frostOct 7
2012 zone4b

Same zone as on the 2012 map. 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 Nikiski, 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 Nikiski, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 7median — 50% chance of a later frost
Safe for tender plantsMay 25only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 20
Growing season151 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 23 and returns around October 19.

From the NOAA station Big River Lakes, AK — 29 miles away, elevation 59 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 99635

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 26 – Apr 9
SpinachSow outdoors · Mar 26 – Apr 16
Broccoli, cabbageStart indoors · Feb 26 – Mar 12
Broccoli, cabbageTransplant · Apr 16 – Apr 30
Onion setsPlant outdoors · Apr 9 – Apr 23
PotatoesPlant outdoors · Apr 16 – Apr 30
LettuceSow outdoors · Apr 9 – Apr 23
Carrots, beetsSow outdoors · Apr 16 – Apr 30
TomatoesStart indoors · Mar 12 – Mar 26
TomatoesTransplant · May 14 – May 28
Peppers, eggplantStart indoors · Feb 26 – Mar 12
Peppers, eggplantTransplant · May 21 – Jun 4
BeansSow outdoors · May 14 – May 28
Sweet cornSow outdoors · May 14 – May 28
Cucumbers, squashSow outdoors · May 14 – May 28
Fall lettuce, spinachSow outdoors · Aug 12 – Aug 26
GarlicPlant cloves · Sep 23 – Oct 28
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 7) and first fall frost (Oct 7) 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 Nikiski, AK.

Soil in Nikiski, AK

The soil mapped at the center of ZIP 99635 is E23-boreal alpine dwarf scrub-gravelly colluvial slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH4.0strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Cook Inlet Mountains-Boreal Alpine-Barren Mountains.

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 99635; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Nikiski, AK

Summer high69 °Faverage high, July
Winter low13 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights184nights a year at 32 °F or less
Growing degree days946base 50 °F — the season’s usable heat
Longest day19 h 18 mindaylight on June 21
Shortest day5 h 30 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation55.1 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 25 °F, low 13 °F 25°13° JanFebruary: average high 31 °F, low 18 °F 31°18° FebMarch: average high 35 °F, low 20 °F 35°20° MarApril: average high 46 °F, low 31 °F 46°31° AprMay: average high 59 °F, low 39 °F 59°39° MayJune: average high 67 °F, low 47 °F 67°47° JunJuly: average high 69 °F, low 51 °F 69°51° JulAugust: average high 67 °F, low 50 °F 67°50° AugSeptember: average high 58 °F, low 44 °F 58°44° SepOctober: average high 46 °F, low 34 °F 46°34° OctNovember: average high 32 °F, low 22 °F 32°22° NovDecember: average high 27 °F, low 17 °F 27°17° Dec

Precipitation by month inches

0″2″4″6″8″January: 4.24 in precipitation 4.2 JanFebruary: 4.63 in precipitation 4.6 FebMarch: 3.06 in precipitation 3.1 MarApril: 2.68 in precipitation 2.7 AprMay: 3.05 in precipitation 3.0 MayJune: 2.83 in precipitation 2.8 JunJuly: 4.22 in precipitation 4.2 JulAugust: 5.41 in precipitation 5.4 AugSeptember: 7.27 in precipitation 7.3 SepOctober: 7.29 in precipitation 7.3 OctNovember: 5.28 in precipitation 5.3 NovDecember: 5.17 in precipitation 5.2 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Big River Lakes, AK (29 mi away); precipitation: Big River Lakes, AK (29 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

4 of the 6 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996674b
Skwentna, AK · 52 mi
996534a
Port Alsworth, AK · 78 mi
996474b
Pedro Bay, AK · 90 mi
996395b
Ninilchik, AK · 90 mi
995566a
Anchor Point, AK · 98 mi
996912b
Nikolai, AK · 116 mi

Alaska planting zones →

Questions about 99635

What planting zone is ZIP code 99635?

ZIP code 99635 (Nikiski, 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 Nikiski, AK?

The median last spring frost (32 °F) near 99635 is May 7; after May 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Big River Lakes station.

When is the first frost in Nikiski, AK?

The median first fall frost near 99635 is October 7, giving a median frost-free growing season of 151 days.

When should I plant tomatoes in 99635?

Start tomato seeds indoors around Mar 12 – Mar 26 and set transplants outside around May 14 – May 28, one to three weeks after the median last frost.

How much rain and snow does 99635 get?

About 55.1 inches of precipitation a year (NOAA 1991–2020 normals, Big River Lakes station).

How hot do summers get in Nikiski, AK?

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

What kind of soil does 99635 have?

The USDA soil survey maps E23-boreal alpine dwarf scrub-gravelly colluvial slopes at the center of ZIP 99635: slightly decomposed plant material, well drained, pH about 4.0 (strongly acidic).

What kind of onions grow in Nikiski, AK?

Long-day onions: the longest day near 99635 is 19 h 18 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).