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

Planting zone for 99672 — Sterling, AK

ZIP code 99672 (Sterling, Kenai Peninsula County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 20 and the first fall frost September 21.

Where ZIP 99672 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 20

First frostSep 21

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 Sterling, 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 Sterling, 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 — 7 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 99672

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 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 Sterling, AK.

Soil in Sterling, AK

The soil mapped at the center of ZIP 99672 is Soldotna — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer

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

DrainageWell drainednatural drainage class

Organic matter82.5%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Soldotna silt loam, sandy substratum, undulating.

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 99672; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Sterling, 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 day19 h 06 mindaylight on June 21

Shortest day5 h 41 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 (7 mi away); precipitation: Sterling 6sw, AK (7 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.

Clam Gulch, AK · 21 mi

996104b

Kasilof, AK · 26 mi

995725a

Cooper Landing, AK · 28 mi

996825a

Tyonek, AK · 45 mi

995115a

Anchorage, AK · 47 mi

996395b

Ninilchik, AK · 48 mi

Alaska planting zones →

Questions about 99672

What planting zone is ZIP code 99672?

ZIP code 99672 (Sterling, 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 Sterling, AK?

The median last spring frost (32 °F) near 99672 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 Sterling, AK?

The median first fall frost near 99672 is September 21, giving a median frost-free growing season of 123 days.

When should I plant tomatoes in 99672?

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 99672 get?

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

How hot do summers get in Sterling, 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 99672 have?

The USDA soil survey maps Soldotna at the center of ZIP 99672: moderately decomposed plant material, well drained, pH about 4.5 (strongly acidic).

What kind of onions grow in Sterling, AK?

Long-day onions: the longest day near 99672 is 19 h 06 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).