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

Planting zone for 99685 — Unalaska, AK

ZIP code 99685 (Unalaska, Aleutians West (CA) County) is in USDA zone 8a: the coldest winter night averages 10 to 15 °F. The median last spring frost is May 6 and the first fall frost October 18.

Where ZIP 99685 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.

Zone8a10 to 15 °F
Coldest night−12.2 to −9.4 °C
Last frostMay 6
First frostOct 18
2012 zone7b

Was 7b 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 8a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Unalaska, 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 Unalaska, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 6median — 50% chance of a later frost
Safe for tender plantsMay 22only 10% chance of frost after
First fall frostOctober 18median — 10% chance by Sep 20
Growing season164 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 19 and returns around November 4.

From the NOAA station Dutch Harbor, AK — 3 miles away, elevation 10 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 99685

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 25 – Apr 8
SpinachSow outdoors · Mar 25 – Apr 15
Broccoli, cabbageStart indoors · Feb 25 – Mar 11
Broccoli, cabbageTransplant · Apr 15 – Apr 29
Onion setsPlant outdoors · Apr 8 – Apr 22
PotatoesPlant outdoors · Apr 15 – Apr 29
LettuceSow outdoors · Apr 8 – Apr 22
Carrots, beetsSow outdoors · Apr 15 – Apr 29
TomatoesStart indoors · Mar 11 – Mar 25
TomatoesTransplant · May 13 – May 27
Peppers, eggplantStart indoors · Feb 25 – Mar 11
Peppers, eggplantTransplant · May 20 – Jun 3
BeansSow outdoors · May 13 – May 27
Sweet cornSow outdoors · May 13 – May 27
Cucumbers, squashSow outdoors · May 13 – May 27
Fall lettuce, spinachSow outdoors · Aug 23 – Sep 6
GarlicPlant cloves · Oct 4 – Nov 8
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 6) and first fall frost (Oct 18) 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 8a in Alaska

292 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive 10 °F or colder — the bottom of zone 8a. Each links to its USDA PLANTS profile.

Trees 16

Alaska cedar75 ft · blooms mid spring · low shade tolerance · to −22 °Fbalsam 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 °Fmountain hemlock125 ft · blooms early summer · low shade tolerance · to −18 °FPacific silver fir165 ft · blooms late spring · low shade tolerance · to −28 °F

Shrubs 51

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 125

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 89

Alaska brome5 ft · blooms late spring · low shade tolerance · to −18 °FAlaska 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 °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 Unalaska, AK.

Soil in Unalaska, AK

The soil mapped at the center of ZIP 99685 is E26-Maritime herbaceous-ashy slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH6.4slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter80%high
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Aleutian Islands-Western Alaska Peninsula-Maritime Upland-Rounded Mountains and Hills.

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 99685; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Unalaska, AK

Summer high59 °Faverage high, August
Winter low29 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights112nights a year at 32 °F or less
Growing degree days250base 50 °F — the season’s usable heat
Longest day17 h 07 mindaylight on June 21
Shortest day7 h 24 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation60.1 inper year, rain and melted snow
Snowfall82 inper year; 70 days with snow on the ground

Average high and low, by month

20°30°40°50°60°70°32 °FJanuary: average high 37 °F, low 29 °F 37°29° JanFebruary: average high 39 °F, low 29 °F 39°29° FebMarch: average high 39 °F, low 29 °F 39°29° MarApril: average high 42 °F, low 33 °F 42°33° AprMay: average high 47 °F, low 37 °F 47°37° MayJune: average high 52 °F, low 42 °F 52°42° JunJuly: average high 57 °F, low 47 °F 57°47° JulAugust: average high 59 °F, low 48 °F 59°48° AugSeptember: average high 55 °F, low 44 °F 55°44° SepOctober: average high 48 °F, low 38 °F 48°38° OctNovember: average high 43 °F, low 33 °F 43°33° NovDecember: average high 39 °F, low 31 °F 39°31° Dec

Precipitation by month inches · ❄ = snowfall

0″2″4″6″8″January: 6.79 in precipitation, 22 in snowfall 6.8❄22 JanFebruary: 5.18 in precipitation, 14.2 in snowfall 5.2❄14 FebMarch: 4.65 in precipitation, 16.5 in snowfall 4.7❄17 MarApril: 3.47 in precipitation, 6.3 in snowfall 3.5❄6 AprMay: 4.20 in precipitation, 0.2 in snowfall 4.2 MayJune: 2.52 in precipitation 2.5 JunJuly: 2.30 in precipitation 2.3 JulAugust: 2.86 in precipitation 2.9 AugSeptember: 5.73 in precipitation 5.7 SepOctober: 7.89 in precipitation, 0.4 in snowfall 7.9 OctNovember: 6.66 in precipitation, 6.2 in snowfall 6.7❄6 NovDecember: 7.88 in precipitation, 15.8 in snowfall 7.9❄16 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Dutch Harbor, AK (3 mi away); precipitation: Dutch Harbor, AK (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 2 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996928b
Dutch Harbor, AK · 3 mi
995538a
Akutan, AK · 31 mi

Alaska planting zones →

Questions about 99685

What planting zone is ZIP code 99685?

ZIP code 99685 (Unalaska, AK) is in USDA hardiness zone 8a on the 2023 map: the coldest night of an average winter reaches 10 to 15 °F (−12.2 to −9.4 °C).

When is the last frost in Unalaska, AK?

The median last spring frost (32 °F) near 99685 is May 6; after May 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Dutch Harbor station.

When is the first frost in Unalaska, AK?

The median first fall frost near 99685 is October 18, giving a median frost-free growing season of 164 days.

When should I plant tomatoes in 99685?

Start tomato seeds indoors around Mar 11 – Mar 25 and set transplants outside around May 13 – May 27, one to three weeks after the median last frost.

How much rain and snow does 99685 get?

About 60.1 inches of precipitation a year and 82 inches of snowfall (NOAA 1991–2020 normals, Dutch Harbor station).

How hot do summers get in Unalaska, AK?

The average high peaks at 59 °F in August, with about 0 days a year at 90 °F or more.

What kind of soil does 99685 have?

The USDA soil survey maps E26-Maritime herbaceous-ashy slopes at the center of ZIP 99685: slightly decomposed plant material, well drained, pH about 6.4 (slightly acidic).

What kind of onions grow in Unalaska, AK?

Long-day onions: the longest day near 99685 is 17 h 07 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99685 change?

Yes. The 2012 USDA map put 99685 in zone 7b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.