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

Planting zone for 99664 — Seward, AK

ZIP code 99664 (Seward, Kenai Peninsula County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 2 and the first fall frost October 7.

Where ZIP 99664 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.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostMay 2
First frostOct 7
2012 zone6a

Was 6a on the 2012 map — half a zone colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Seward, 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 Seward, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 2median — 50% chance of a later frost
Safe for tender plantsMay 17only 10% chance of frost after
First fall frostOctober 7median — 10% chance by Sep 28
Growing season158 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 15 and returns around October 21.

From the NOAA station Seward Airport, AK — 3 miles away, elevation 23 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 99664

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 21 – Apr 4
SpinachSow outdoors · Mar 21 – Apr 11
Broccoli, cabbageStart indoors · Feb 21 – Mar 7
Broccoli, cabbageTransplant · Apr 11 – Apr 25
Onion setsPlant outdoors · Apr 4 – Apr 18
PotatoesPlant outdoors · Apr 11 – Apr 25
LettuceSow outdoors · Apr 4 – Apr 18
Carrots, beetsSow outdoors · Apr 11 – Apr 25
TomatoesStart indoors · Mar 7 – Mar 21
TomatoesTransplant · May 9 – May 23
Peppers, eggplantStart indoors · Feb 21 – Mar 7
Peppers, eggplantTransplant · May 16 – May 30
BeansSow outdoors · May 9 – May 23
Sweet cornSow outdoors · May 9 – May 23
Cucumbers, squashSow outdoors · May 9 – May 23
Fall lettuce, spinachSow outdoors · Aug 12 – Aug 26
GarlicPlant cloves · Sep 23 – Oct 28
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 2) and first fall frost (Oct 7) 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 5b in Alaska

282 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. 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 47

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 122

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 Seward, AK.

Soil in Seward, AK

The soil mapped at the center of ZIP 99664 is Aialik — moderately decomposed plant material, well drained.

TextureModerately decomposed plant materialtop layer
pH4.3strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter75%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Rock outcrop-Aialik-Snow complex, 10 to 100 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 99664; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Seward, AK

Summer high62 °Faverage high, July
Winter low21 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights146nights a year at 32 °F or less
Growing degree days539base 50 °F — the season’s usable heat
Longest day18 h 55 mindaylight on June 21
Shortest day5 h 49 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation69.7 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°32 °FJanuary: average high 31 °F, low 21 °F 31°21° JanFebruary: average high 34 °F, low 24 °F 34°24° FebMarch: average high 37 °F, low 25 °F 37°25° MarApril: average high 45 °F, low 32 °F 45°32° AprMay: average high 53 °F, low 39 °F 53°39° MayJune: average high 59 °F, low 46 °F 59°46° JunJuly: average high 62 °F, low 50 °F 62°50° JulAugust: average high 62 °F, low 50 °F 62°50° AugSeptember: average high 56 °F, low 43 °F 56°43° SepOctober: average high 46 °F, low 35 °F 46°35° OctNovember: average high 36 °F, low 27 °F 36°27° NovDecember: average high 33 °F, low 23 °F 33°23° Dec

Precipitation by month inches

0″2″4″6″8″10″January: 6.47 in precipitation 6.5 JanFebruary: 6.35 in precipitation 6.3 FebMarch: 3.85 in precipitation 3.9 MarApril: 4.29 in precipitation 4.3 AprMay: 3.50 in precipitation 3.5 MayJune: 2.34 in precipitation 2.3 JunJuly: 3.11 in precipitation 3.1 JulAugust: 5.39 in precipitation 5.4 AugSeptember: 9.90 in precipitation 9.9 SepOctober: 8.69 in precipitation 8.7 OctNovember: 7.60 in precipitation 7.6 NovDecember: 8.22 in precipitation 8.2 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Seward Airport, AK (3 mi away); precipitation: Seward Airport, AK (3 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.

995725a
Cooper Landing, AK · 31 mi
996315a
Moose Pass, AK · 32 mi
995685a
Clam Gulch, AK · 39 mi
996055b
Hope, AK · 51 mi
995405b
Indian, AK · 61 mi
995875b
Girdwood, AK · 61 mi
996115a
Kenai, AK · 64 mi
995115a
Anchorage, AK · 65 mi

Alaska planting zones →

Questions about 99664

What planting zone is ZIP code 99664?

ZIP code 99664 (Seward, AK) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Seward, AK?

The median last spring frost (32 °F) near 99664 is May 2; after May 17 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Seward Airport station.

When is the first frost in Seward, AK?

The median first fall frost near 99664 is October 7, giving a median frost-free growing season of 158 days.

When should I plant tomatoes in 99664?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 99664 get?

About 69.7 inches of precipitation a year (NOAA 1991–2020 normals, Seward Airport station).

How hot do summers get in Seward, AK?

The average high peaks at 62 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99664 have?

The USDA soil survey maps Aialik at the center of ZIP 99664: moderately decomposed plant material, well drained, pH about 4.3 (strongly acidic).

What kind of onions grow in Seward, AK?

Long-day onions: the longest day near 99664 is 18 h 55 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99664 change?

Yes. The 2012 USDA map put 99664 in zone 6a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.