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

Planting zone for 99918 — Coffman Cove, AK

ZIP code 99918 (Coffman Cove, Prince of Wales-Hyder County) is in USDA zone 8a: the coldest winter night averages 10 to 15 °F. The median last spring frost is May 1 and the first fall frost October 13.

Where ZIP 99918 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 1
First frostOct 13
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 Coffman Cove, 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 Coffman Cove, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 1median — 50% chance of a later frost
Safe for tender plantsMay 16only 10% chance of frost after
First fall frostOctober 13median — 10% chance by Oct 1
Growing season166 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 11 and returns around October 30.

From the NOAA station Thorne Bay, AK — 17 miles away, elevation 285 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 99918

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 20 – Apr 3
SpinachSow outdoors · Mar 20 – Apr 10
Broccoli, cabbageStart indoors · Feb 20 – Mar 6
Broccoli, cabbageTransplant · Apr 10 – Apr 24
Onion setsPlant outdoors · Apr 3 – Apr 17
PotatoesPlant outdoors · Apr 10 – Apr 24
LettuceSow outdoors · Apr 3 – Apr 17
Carrots, beetsSow outdoors · Apr 10 – Apr 24
TomatoesStart indoors · Mar 6 – Mar 20
TomatoesTransplant · May 8 – May 22
Peppers, eggplantStart indoors · Feb 20 – Mar 6
Peppers, eggplantTransplant · May 15 – May 29
BeansSow outdoors · May 8 – May 22
Sweet cornSow outdoors · May 8 – May 22
Cucumbers, squashSow outdoors · May 8 – May 22
Fall lettuce, spinachSow outdoors · Aug 18 – Sep 1
GarlicPlant cloves · Sep 29 – Nov 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 1) and first fall frost (Oct 13) 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 Coffman Cove, AK.

Soil in Coffman Cove, AK

The soil mapped at the center of ZIP 99918 is Hydaburg — peat, very poorly drained.

TexturePeattop layer
pH3.8strongly acidic; most vegetables like 6.0–7.0
DrainageVery poorly drainedconsider raised beds
Organic matter92.5%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Hydaburg-Sunnyhay association, 5 to 75 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 99918; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Coffman Cove, AK

Summer high66 °Faverage high, July
Winter low28 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights118nights a year at 32 °F or less
Growing degree days765base 50 °F — the season’s usable heat
Longest day17 h 36 mindaylight on June 21
Shortest day6 h 58 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation85.2 inper year, rain and melted snow

Average high and low, by month

20°30°40°50°60°70°80°32 °FJanuary: average high 38 °F, low 28 °F 38°28° JanFebruary: average high 40 °F, low 28 °F 40°28° FebMarch: average high 43 °F, low 30 °F 43°30° MarApril: average high 50 °F, low 34 °F 50°34° AprMay: average high 57 °F, low 40 °F 57°40° MayJune: average high 63 °F, low 46 °F 63°46° JunJuly: average high 66 °F, low 51 °F 66°51° JulAugust: average high 65 °F, low 50 °F 65°50° AugSeptember: average high 59 °F, low 45 °F 59°45° SepOctober: average high 51 °F, low 38 °F 51°38° OctNovember: average high 42 °F, low 32 °F 42°32° NovDecember: average high 38 °F, low 30 °F 38°30° Dec

Precipitation by month inches

0″2″4″6″8″10″12″January: 8.16 in precipitation 8.2 JanFebruary: 5.46 in precipitation 5.5 FebMarch: 6.25 in precipitation 6.3 MarApril: 5.09 in precipitation 5.1 AprMay: 3.51 in precipitation 3.5 MayJune: 4.08 in precipitation 4.1 JunJuly: 5.30 in precipitation 5.3 JulAugust: 6.98 in precipitation 7.0 AugSeptember: 8.63 in precipitation 8.6 SepOctober: 12.12 in precipitation 12.1 OctNovember: 10.52 in precipitation 10.5 NovDecember: 9.08 in precipitation 9.1 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Thorne Bay, AK (17 mi away); precipitation: Thorne Bay, AK (17 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

999197b
Thorne Bay, AK · 20 mi
999037b
Meyers Chuck, AK · 26 mi
999257b
Klawock, AK · 27 mi
999217b
Craig, AK · 28 mi
999297b
Wrangell, AK · 36 mi
999228a
Hydaburg, AK · 44 mi
999278a
Point Baker, AK · 45 mi
999288a
Ward Cove, AK · 54 mi

Alaska planting zones →

Questions about 99918

What planting zone is ZIP code 99918?

ZIP code 99918 (Coffman Cove, 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 Coffman Cove, AK?

The median last spring frost (32 °F) near 99918 is May 1; after May 16 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Thorne Bay station.

When is the first frost in Coffman Cove, AK?

The median first fall frost near 99918 is October 13, giving a median frost-free growing season of 166 days.

When should I plant tomatoes in 99918?

Start tomato seeds indoors around Mar 6 – Mar 20 and set transplants outside around May 8 – May 22, one to three weeks after the median last frost.

How much rain and snow does 99918 get?

About 85.2 inches of precipitation a year (NOAA 1991–2020 normals, Thorne Bay station).

How hot do summers get in Coffman Cove, 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 99918 have?

The USDA soil survey maps Hydaburg at the center of ZIP 99918: peat, very poorly drained, pH about 3.8 (strongly acidic).

What kind of onions grow in Coffman Cove, AK?

Long-day onions: the longest day near 99918 is 17 h 36 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99918 change?

Yes. The 2012 USDA map put 99918 in zone 7b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.