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

Planting zone for 99643 — Old Harbor, AK

ZIP code 99643 (Old Harbor, Kodiak Island County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is May 5 and the first fall frost October 3.

Where ZIP 99643 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.

Zone7b5 to 10 °F
Coldest night−15 to −12.2 °C
Last frostMay 5
First frostOct 3
2012 zone7a

Was 7a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 7b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Old Harbor, 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 Old Harbor, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 5median — 50% chance of a later frost
Safe for tender plantsMay 21only 10% chance of frost after
First fall frostOctober 3median — 10% chance by Sep 22
Growing season151 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 18 and returns around October 17.

From the NOAA station Kodiak Airport, AK — 48 miles away, elevation 79 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 99643

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 24 – Apr 7
SpinachSow outdoors · Mar 24 – Apr 14
Broccoli, cabbageStart indoors · Feb 24 – Mar 10
Broccoli, cabbageTransplant · Apr 14 – Apr 28
Onion setsPlant outdoors · Apr 7 – Apr 21
PotatoesPlant outdoors · Apr 14 – Apr 28
LettuceSow outdoors · Apr 7 – Apr 21
Carrots, beetsSow outdoors · Apr 14 – Apr 28
TomatoesStart indoors · Mar 10 – Mar 24
TomatoesTransplant · May 12 – May 26
Peppers, eggplantStart indoors · Feb 24 – Mar 10
Peppers, eggplantTransplant · May 19 – Jun 2
BeansSow outdoors · May 12 – May 26
Sweet cornSow outdoors · May 12 – May 26
Cucumbers, squashSow outdoors · May 12 – May 26
Fall lettuce, spinachSow outdoors · Aug 8 – Aug 22
GarlicPlant cloves · Sep 19 – Oct 24
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 5) and first fall frost (Oct 3) 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.

Soil in Old Harbor, AK

The soil mapped at the center of ZIP 99643 is Akalura — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer
pH4.4strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Akalura-Kaguyak-Bidarka complex, 3 to 35 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 99643; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Old Harbor, AK

Summer high63 °Faverage high, August
Winter low26 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights133nights a year at 32 °F or less
Growing degree days551base 50 °F — the season’s usable heat
Longest day17 h 57 mindaylight on June 21
Shortest day6 h 39 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation78.3 inper year, rain and melted snow
Snowfall70 inper year; 47 days with snow on the ground

Average high and low, by month

20°30°40°50°60°70°32 °FJanuary: average high 36 °F, low 26 °F 36°26° JanFebruary: average high 38 °F, low 27 °F 38°27° FebMarch: average high 39 °F, low 28 °F 39°28° MarApril: average high 45 °F, low 34 °F 45°34° AprMay: average high 52 °F, low 40 °F 52°40° MayJune: average high 57 °F, low 46 °F 57°46° JunJuly: average high 62 °F, low 51 °F 62°51° JulAugust: average high 63 °F, low 50 °F 63°50° AugSeptember: average high 57 °F, low 44 °F 57°44° SepOctober: average high 48 °F, low 36 °F 48°36° OctNovember: average high 41 °F, low 30 °F 41°30° NovDecember: average high 37 °F, low 27 °F 37°27° Dec

Precipitation by month inches · ❄ = snowfall

0″2″4″6″8″January: 8.35 in precipitation, 14.5 in snowfall 8.3❄15 JanFebruary: 6.31 in precipitation, 14.4 in snowfall 6.3❄14 FebMarch: 4.82 in precipitation, 12.3 in snowfall 4.8❄12 MarApril: 6.14 in precipitation, 6.2 in snowfall 6.1❄6 AprMay: 5.85 in precipitation, 0.5 in snowfall 5.8❄1 MayJune: 5.17 in precipitation 5.2 JunJuly: 4.51 in precipitation 4.5 JulAugust: 4.90 in precipitation 4.9 AugSeptember: 7.55 in precipitation 7.5 SepOctober: 8.85 in precipitation, 0.7 in snowfall 8.8❄1 OctNovember: 7.06 in precipitation, 6.1 in snowfall 7.1❄6 NovDecember: 8.81 in precipitation, 15.6 in snowfall 8.8❄16 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Kodiak Airport, AK (48 mi away); precipitation: Kodiak Airport, AK (48 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

3 of the 7 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996247b
Larsen Bay, AK · 27 mi
996157a
Kodiak, AK · 32 mi
996087a
Karluk, AK · 46 mi
995507a
Port Lions, AK · 48 mi
996197b
Kodiak, AK · 52 mi
996977b
Kodiak, AK · 52 mi
996447b
Ouzinkie, AK · 59 mi

Alaska planting zones →

Questions about 99643

What planting zone is ZIP code 99643?

ZIP code 99643 (Old Harbor, AK) is in USDA hardiness zone 7b on the 2023 map: the coldest night of an average winter reaches 5 to 10 °F (−15 to −12.2 °C).

When is the last frost in Old Harbor, AK?

The median last spring frost (32 °F) near 99643 is May 5; after May 21 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Kodiak Airport station.

When is the first frost in Old Harbor, AK?

The median first fall frost near 99643 is October 3, giving a median frost-free growing season of 151 days.

When should I plant tomatoes in 99643?

Start tomato seeds indoors around Mar 10 – Mar 24 and set transplants outside around May 12 – May 26, one to three weeks after the median last frost.

How much rain and snow does 99643 get?

About 78.3 inches of precipitation a year and 70 inches of snowfall (NOAA 1991–2020 normals, Kodiak Airport station).

How hot do summers get in Old Harbor, AK?

The average high peaks at 63 °F in August, with about 0 days a year at 90 °F or more.

What kind of soil does 99643 have?

The USDA soil survey maps Akalura at the center of ZIP 99643: moderately decomposed plant material, well drained, pH about 4.4 (strongly acidic).

What kind of onions grow in Old Harbor, AK?

Long-day onions: the longest day near 99643 is 17 h 57 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99643 change?

Yes. The 2012 USDA map put 99643 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.