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

Planting zone for 99660 — Saint Paul Island, AK

ZIP code 99660 (Saint Paul Island, Aleutians West (CA) County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is June 4 and the first fall frost September 28.

Where ZIP 99660 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.

Zone6b−5 to 0 °F
Coldest night−20.6 to −17.8 °C
Last frostJun 4
First frostSep 28
2012 zone6b

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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Saint Paul Island, 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 Saint Paul Island, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostJune 4median — 50% chance of a later frost
Safe for tender plantsJune 25only 10% chance of frost after
First fall frostSeptember 28median — 10% chance by Sep 11
Growing season114 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 17 and returns around October 15.

From the NOAA station St Paul Island Airport, AK — 4 miles away, elevation 36 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 99660

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 23 – May 7
SpinachSow outdoors · Apr 23 – May 14
Broccoli, cabbageStart indoors · Mar 26 – Apr 9
Broccoli, cabbageTransplant · May 14 – May 28
Onion setsPlant outdoors · May 7 – May 21
PotatoesPlant outdoors · May 14 – May 28
LettuceSow outdoors · May 7 – May 21
Carrots, beetsSow outdoors · May 14 – May 28
TomatoesStart indoors · Apr 9 – Apr 23
TomatoesTransplant · Jun 11 – Jun 25
Peppers, eggplantStart indoors · Mar 26 – Apr 9
Peppers, eggplantTransplant · Jun 18 – Jul 2
BeansSow outdoors · Jun 11 – Jun 25
Sweet cornSow outdoors · Jun 11 – Jun 25
Cucumbers, squashSow outdoors · Jun 11 – Jun 25
Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17
GarlicPlant cloves · Sep 14 – Oct 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 4) and first fall frost (Sep 28) 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 6b in Alaska

286 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. 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 49

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 124

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 88

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 Saint Paul Island, AK.

Soil in Saint Paul Island, AK

The soil mapped at the center of ZIP 99660 is Lithic Haplocryands — stony slightly decomposed plant material, well drained.

TextureStony slightly decomposed plant materialtop layer
pH6.2slightly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter90%high
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Lithic Haplocryands, rubbly-Typic Haplocryands, moderately deep-Rock outcrop complex, 1 to 8 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 99660; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Saint Paul Island, AK

Summer high53 °Faverage high, August
Winter low21 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights176nights a year at 32 °F or less
Growing degree days46base 50 °F — the season’s usable heat
Longest day17 h 56 mindaylight on June 21
Shortest day6 h 40 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation24.3 inper year, rain and melted snow
Snowfall64 inper year; 109 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°32 °FJanuary: average high 29 °F, low 21 °F 29°21° JanFebruary: average high 29 °F, low 21 °F 29°21° FebMarch: average high 30 °F, low 21 °F 30°21° MarApril: average high 34 °F, low 26 °F 34°26° AprMay: average high 41 °F, low 32 °F 41°32° MayJune: average high 48 °F, low 39 °F 48°39° JunJuly: average high 52 °F, low 44 °F 52°44° JulAugust: average high 53 °F, low 46 °F 53°46° AugSeptember: average high 50 °F, low 42 °F 50°42° SepOctober: average high 44 °F, low 35 °F 44°35° OctNovember: average high 38 °F, low 30 °F 38°30° NovDecember: average high 33 °F, low 25 °F 33°25° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″January: 1.61 in precipitation, 16.5 in snowfall 1.6❄17 JanFebruary: 1.43 in precipitation, 11.1 in snowfall 1.4❄11 FebMarch: 1.29 in precipitation, 9.6 in snowfall 1.3❄10 MarApril: 1.04 in precipitation, 5.3 in snowfall 1.0❄5 AprMay: 1.02 in precipitation, 0.8 in snowfall 1.0❄1 MayJune: 1.31 in precipitation 1.3 JunJuly: 1.98 in precipitation 2.0 JulAugust: 3.06 in precipitation 3.1 AugSeptember: 3.00 in precipitation 3.0 SepOctober: 3.32 in precipitation, 1.6 in snowfall 3.3❄2 OctNovember: 2.97 in precipitation, 7.1 in snowfall 3.0❄7 NovDecember: 2.30 in precipitation, 12.3 in snowfall 2.3❄12 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: St Paul Island Airport, AK (4 mi away); precipitation: St Paul Island Airport, AK (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

995917a
Saint George Island, AK · 47 mi

Alaska planting zones →

Questions about 99660

What planting zone is ZIP code 99660?

ZIP code 99660 (Saint Paul Island, AK) is in USDA hardiness zone 6b on the 2023 map: the coldest night of an average winter reaches −5 to 0 °F (−20.6 to −17.8 °C).

When is the last frost in Saint Paul Island, AK?

The median last spring frost (32 °F) near 99660 is June 4; after June 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, St Paul Island Airport station.

When is the first frost in Saint Paul Island, AK?

The median first fall frost near 99660 is September 28, giving a median frost-free growing season of 114 days.

When should I plant tomatoes in 99660?

Start tomato seeds indoors around Apr 9 – Apr 23 and set transplants outside around Jun 11 – Jun 25, one to three weeks after the median last frost.

How much rain and snow does 99660 get?

About 24.3 inches of precipitation a year and 64 inches of snowfall (NOAA 1991–2020 normals, St Paul Island Airport station).

How hot do summers get in Saint Paul Island, AK?

The average high peaks at 53 °F in August, with about 0 days a year at 90 °F or more.

What kind of soil does 99660 have?

The USDA soil survey maps Lithic Haplocryands at the center of ZIP 99660: stony slightly decomposed plant material, well drained, pH about 6.2 (slightly acidic).

What kind of onions grow in Saint Paul Island, AK?

Long-day onions: the longest day near 99660 is 17 h 56 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).