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

Planting zone for 99568 — Clam Gulch, AK

ZIP code 99568 (Clam Gulch, Kenai Peninsula County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 20 and the first fall frost September 21.

Where ZIP 99568 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostMay 20

First frostSep 21

2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Clam Gulch, 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 Clam Gulch, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 20median — 50% chance of a later frost

Safe for tender plantsJune 1only 10% chance of frost after

First fall frostSeptember 21median — 10% chance by Sep 6

Growing season123 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around September 30.

From the NOAA station Sterling 6sw, AK — 19 miles away, elevation 292 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 99568

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 8 – Apr 22

SpinachSow outdoors · Apr 8 – Apr 29

Broccoli, cabbageStart indoors · Mar 11 – Mar 25

Broccoli, cabbageTransplant · Apr 29 – May 13

Onion setsPlant outdoors · Apr 22 – May 6

PotatoesPlant outdoors · Apr 29 – May 13

LettuceSow outdoors · Apr 22 – May 6

Carrots, beetsSow outdoors · Apr 29 – May 13

TomatoesStart indoors · Mar 25 – Apr 8

TomatoesTransplant · May 27 – Jun 10

Peppers, eggplantStart indoors · Mar 11 – Mar 25

Peppers, eggplantTransplant · Jun 3 – Jun 17

BeansSow outdoors · May 27 – Jun 10

Sweet cornSow outdoors · May 27 – Jun 10

Cucumbers, squashSow outdoors · May 27 – Jun 10

Fall lettuce, spinachSow outdoors · Jul 27 – Aug 10

GarlicPlant cloves · Sep 7 – Oct 12

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 20) and first fall frost (Sep 21) 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 5a in Alaska

275 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Clam Gulch, AK.

Soil in Clam Gulch, AK

The soil mapped at the center of ZIP 99568 is E23-boreal forest-silty till slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter75%high

Hydrologic groupAwater soaks in fast

Map unit: Cook Inlet Mountains-Boreal Upland-Rounded 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 99568; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Clam Gulch, AK

Summer high66 °Faverage high, July

Winter low8 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights200nights a year at 32 °F or less

Growing degree days570base 50 °F — the season’s usable heat

Longest day18 h 58 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)

Precipitation23.1 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: Sterling 6sw, AK (19 mi away); precipitation: Sterling 6sw, AK (19 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Cooper Landing, AK · 29 mi

Anchorage, AK · 61 mi

995155a

Anchorage, AK · 63 mi

Alaska planting zones →

Questions about 99568

What planting zone is ZIP code 99568?

ZIP code 99568 (Clam Gulch, AK) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Clam Gulch, AK?

The median last spring frost (32 °F) near 99568 is May 20; after June 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Sterling 6sw station.

When is the first frost in Clam Gulch, AK?

The median first fall frost near 99568 is September 21, giving a median frost-free growing season of 123 days.

When should I plant tomatoes in 99568?

Start tomato seeds indoors around Mar 25 – Apr 8 and set transplants outside around May 27 – Jun 10, one to three weeks after the median last frost.

How much rain and snow does 99568 get?

About 23.1 inches of precipitation a year (NOAA 1991–2020 normals, Sterling 6sw station).

How hot do summers get in Clam Gulch, 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 99568 have?

The USDA soil survey maps E23-boreal forest-silty till slopes at the center of ZIP 99568: slightly decomposed plant material, well drained, pH about 5.0 (strongly acidic).

What kind of onions grow in Clam Gulch, AK?

Long-day onions: the longest day near 99568 is 18 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).