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

Planting zone for 99610 — Kasilof, AK

ZIP code 99610 (Kasilof, Kenai Peninsula County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is June 11 and the first fall frost September 1.

Where ZIP 99610 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 frostJun 11

First frostSep 1

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 Kasilof, 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 Kasilof, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 11median — 50% chance of a later frost

Safe for tender plantsJuly 7only 10% chance of frost after

First fall frostSeptember 1median — 10% chance by Aug 11

Growing season75 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 23 and returns around September 16.

From the NOAA station Soldotna 5ssw, AK — 11 miles away, elevation 180 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 99610

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 30 – May 14

SpinachSow outdoors · Apr 30 – May 21

Broccoli, cabbageStart indoors · Apr 2 – Apr 16

Broccoli, cabbageTransplant · May 21 – Jun 4

Onion setsPlant outdoors · May 14 – May 28

PotatoesPlant outdoors · May 21 – Jun 4

LettuceSow outdoors · May 14 – May 28

Carrots, beetsSow outdoors · May 21 – Jun 4

TomatoesStart indoors · Apr 16 – Apr 30

TomatoesTransplant · Jun 18 – Jul 2

Peppers, eggplantStart indoors · Apr 2 – Apr 16

Peppers, eggplantTransplant · Jun 25 – Jul 9

BeansSow outdoors · Jun 18 – Jul 2

Sweet cornSow outdoors · Jun 18 – Jul 2

Cucumbers, squashSow outdoors · Jun 18 – Jul 2

Fall lettuce, spinachSow outdoors · Jul 7 – Jul 21

GarlicPlant cloves · Aug 18 – Sep 22

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 11) and first fall frost (Sep 1) 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.

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 Kasilof, AK.

Soil in Kasilof, AK

The soil mapped at the center of ZIP 99610 is Killey — slightly decomposed plant material, poorly drained.

TextureSlightly decomposed plant materialtop layer

pH4.5strongly acidic; most vegetables like 6.0–7.0

DrainagePoorly drainedconsider raised beds

Organic matter90%high

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Killey and Moose River soils, 0 to 2 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 99610; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Kasilof, AK

Summer high66 °Faverage high, July

Winter low5 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights227nights a year at 32 °F or less

Growing degree days373base 50 °F — the season’s usable heat

Longest day18 h 59 mindaylight on June 21

Shortest day5 h 47 mindaylight on December 21

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

Precipitation21.6 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Soldotna 5ssw, AK (11 mi away); precipitation: Soldotna 5ssw, AK (11 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

6 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996694b

Soldotna, AK · 10 mi

996395b

Ninilchik, AK · 22 mi

995685a

Clam Gulch, AK · 23 mi

996724b

Sterling, AK · 26 mi

995566a

Anchor Point, AK · 33 mi

Alaska planting zones →

Questions about 99610

What planting zone is ZIP code 99610?

ZIP code 99610 (Kasilof, 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 Kasilof, AK?

The median last spring frost (32 °F) near 99610 is June 11; after July 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Soldotna 5ssw station.

When is the first frost in Kasilof, AK?

The median first fall frost near 99610 is September 1, giving a median frost-free growing season of 75 days.

When should I plant tomatoes in 99610?

Start tomato seeds indoors around Apr 16 – Apr 30 and set transplants outside around Jun 18 – Jul 2, one to three weeks after the median last frost.

How much rain and snow does 99610 get?

About 21.6 inches of precipitation a year (NOAA 1991–2020 normals, Soldotna 5ssw station).

How hot do summers get in Kasilof, AK?

The average high peaks at 66 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99610 have?

The USDA soil survey maps Killey at the center of ZIP 99610: slightly decomposed plant material, poorly drained, pH about 4.5 (strongly acidic).

What kind of onions grow in Kasilof, AK?

Long-day onions: the longest day near 99610 is 18 h 59 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).