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

Planting zone for 99587 — Girdwood, AK

ZIP code 99587 (Girdwood, Anchorage Municipality) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 8 and the first fall frost September 29.

Where ZIP 99587 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 8
First frostSep 29
2012 zone5b

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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Girdwood, 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 Girdwood, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 8median — 50% chance of a later frost
Safe for tender plantsMay 22only 10% chance of frost after
First fall frostSeptember 29median — 10% chance by Sep 14
Growing season142 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 26 and returns around October 11.

From the NOAA station Alyeska, AK — 8 miles away, elevation 272 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 99587

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 27 – Apr 10
SpinachSow outdoors · Mar 27 – Apr 17
Broccoli, cabbageStart indoors · Feb 27 – Mar 13
Broccoli, cabbageTransplant · Apr 17 – May 1
Onion setsPlant outdoors · Apr 10 – Apr 24
PotatoesPlant outdoors · Apr 17 – May 1
LettuceSow outdoors · Apr 10 – Apr 24
Carrots, beetsSow outdoors · Apr 17 – May 1
TomatoesStart indoors · Mar 13 – Mar 27
TomatoesTransplant · May 15 – May 29
Peppers, eggplantStart indoors · Feb 27 – Mar 13
Peppers, eggplantTransplant · May 22 – Jun 5
BeansSow outdoors · May 15 – May 29
Sweet cornSow outdoors · May 15 – May 29
Cucumbers, squashSow outdoors · May 15 – May 29
Fall lettuce, spinachSow outdoors · Aug 4 – Aug 18
GarlicPlant cloves · Sep 15 – Oct 20
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 8) and first fall frost (Sep 29) 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 Girdwood, AK.

Soil in Girdwood, AK

The soil mapped at the center of ZIP 99587 is E23-boreal subalpine scrub/meadow mosaic-silty till slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH5.0strongly 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: Cook Inlet Mountains-Boreal Upland and Lowland-Valleys.

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 99587; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Girdwood, AK

Summer high67 °Faverage high, July
Winter low17 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights175nights a year at 32 °F or less
Growing degree days643base 50 °F — the season’s usable heat
Longest day19 h 16 mindaylight on June 21
Shortest day5 h 32 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation75.1 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°32 °FJanuary: average high 27 °F, low 17 °F 27°17° JanFebruary: average high 31 °F, low 19 °F 31°19° FebMarch: average high 36 °F, low 20 °F 36°20° MarApril: average high 46 °F, low 29 °F 46°29° AprMay: average high 55 °F, low 37 °F 55°37° MayJune: average high 64 °F, low 45 °F 64°45° JunJuly: average high 67 °F, low 50 °F 67°50° JulAugust: average high 65 °F, low 48 °F 65°48° AugSeptember: average high 56 °F, low 41 °F 56°41° SepOctober: average high 44 °F, low 32 °F 44°32° OctNovember: average high 33 °F, low 22 °F 33°22° NovDecember: average high 29 °F, low 19 °F 29°19° Dec

Precipitation by month inches

0″2″4″6″8″10″January: 6.89 in precipitation 6.9 JanFebruary: 6.59 in precipitation 6.6 FebMarch: 5.75 in precipitation 5.8 MarApril: 5.93 in precipitation 5.9 AprMay: 4.62 in precipitation 4.6 MayJune: 2.60 in precipitation 2.6 JunJuly: 3.20 in precipitation 3.2 JulAugust: 5.86 in precipitation 5.9 AugSeptember: 9.05 in precipitation 9.1 SepOctober: 8.59 in precipitation 8.6 OctNovember: 7.54 in precipitation 7.5 NovDecember: 8.47 in precipitation 8.5 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Alyeska, AK (8 mi away); precipitation: Mt. Alyeska, AK (7 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.

995405b
Indian, AK · 15 mi
995775a
Eagle River, AK · 20 mi
996055b
Hope, AK · 21 mi
995675a
Chugiak, AK · 24 mi
995075a
Anchorage, AK · 27 mi
995045a
Anchorage, AK · 29 mi
995165b
Anchorage, AK · 29 mi
996937a
Whittier, AK · 29 mi

Alaska planting zones →

Questions about 99587

What planting zone is ZIP code 99587?

ZIP code 99587 (Girdwood, 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 Girdwood, AK?

The median last spring frost (32 °F) near 99587 is May 8; after May 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Alyeska station.

When is the first frost in Girdwood, AK?

The median first fall frost near 99587 is September 29, giving a median frost-free growing season of 142 days.

When should I plant tomatoes in 99587?

Start tomato seeds indoors around Mar 13 – Mar 27 and set transplants outside around May 15 – May 29, one to three weeks after the median last frost.

How much rain and snow does 99587 get?

About 75.1 inches of precipitation a year (NOAA 1991–2020 normals, Mt. Alyeska station).

How hot do summers get in Girdwood, AK?

The average high peaks at 67 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99587 have?

The USDA soil survey maps E23-boreal subalpine scrub/meadow mosaic-silty till slopes at the center of ZIP 99587: slightly decomposed plant material, well drained, pH about 5.0 (strongly acidic).

What kind of onions grow in Girdwood, AK?

Long-day onions: the longest day near 99587 is 19 h 16 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).