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

Planting zone for 99588 — Glennallen, AK

ZIP code 99588 (Glennallen, Copper River Census Area County) is in USDA zone 2b: the coldest winter night averages −45 to −40 °F. The median last spring frost is May 30 and the first fall frost September 4.

Where ZIP 99588 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.

Zone2b−45 to −40 °F
Coldest night−42.8 to −40 °C
Last frostMay 30
First frostSep 4
2012 zone2a

Was 2a 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 2b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Glennallen, 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 Glennallen, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 30median — 50% chance of a later frost
Safe for tender plantsJune 9only 10% chance of frost after
First fall frostSeptember 4median — 10% chance by Aug 17
Growing season95 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 19 and returns around September 17.

From the NOAA station Lake Susitna, AK — 17 miles away, elevation 2,375 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 99588

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 18 – May 2
SpinachSow outdoors · Apr 18 – May 9
Broccoli, cabbageStart indoors · Mar 21 – Apr 4
Broccoli, cabbageTransplant · May 9 – May 23
Onion setsPlant outdoors · May 2 – May 16
PotatoesPlant outdoors · May 9 – May 23
LettuceSow outdoors · May 2 – May 16
Carrots, beetsSow outdoors · May 9 – May 23
TomatoesStart indoors · Apr 4 – Apr 18
TomatoesTransplant · Jun 6 – Jun 20
Peppers, eggplantStart indoors · Mar 21 – Apr 4
Peppers, eggplantTransplant · Jun 13 – Jun 27
BeansSow outdoors · Jun 6 – Jun 20
Sweet cornSow outdoors · Jun 6 – Jun 20
Cucumbers, squashSow outdoors · Jun 6 – Jun 20
Fall lettuce, spinachSow outdoors · Jul 10 – Jul 24
GarlicPlant cloves · Aug 21 – Sep 25
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 30) and first fall frost (Sep 4) 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 2b in Alaska

45 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −45 °F or colder — the bottom of zone 2b. Each links to its USDA PLANTS profile.

Trees 8

balsam 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 °Fpaper birch70 ft · blooms mid spring · high shade tolerance · to −62 °Fquaking aspen65 ft · blooms mid spring · high shade tolerance · to −70 °Fsubalpine fir90 ft · blooms late spring · low shade tolerance · to −51 °F

Shrubs 17

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °Fblack hawthorn15 ft · blooms mid spring · medium shade tolerance · to −47 °Fhalberd willow3 ft · blooms early summer · to −62 °FLapland rosebay3 ft · blooms late spring · low shade tolerance · to −62 °Flingonberry0.5 ft · blooms summer · high shade tolerance · to −62 °FMacKenzie's willow45 ft · blooms early spring · high shade tolerance · to −50 °F

Wildflowers & perennials 12

alpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °Farctic dock1 ft · blooms summer · high shade tolerance · to −62 °Farctic lupine2 ft · blooms spring · medium shade tolerance · to −62 °Farctic poppy1.5 ft · blooms summer · low shade tolerance · to −54 °Farctic raspberry1 ft · blooms summer · high shade tolerance · to −62 °Feightpetal mountain-avens0.3 ft · blooms late spring · medium shade tolerance · to −62 °F

Grasses 6

arctic bluegrass2 ft · high shade tolerance · to −62 °FHoppner's sedge1 ft · high shade tolerance · to −52 °Flargeflower speargrass2 ft · high shade tolerance · to −52 °Flivid sedge1 ft · blooms early summer · high shade tolerance · to −62 °FLyngbye's sedge1 ft · high shade tolerance · to −52 °FRamensk's sedge1 ft · high shade tolerance · to −52 °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 Glennallen, AK.

Soil in Glennallen, AK

The soil mapped at the center of ZIP 99588 is Klasi — peat, poorly drained.

TexturePeattop layer
pH5.8moderately acidic; most vegetables like 6.0–7.0
DrainagePoorly drainedconsider raised beds
Organic matter77.5%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Klasi peat, 0 to 10 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 99588; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Glennallen, AK

Summer high69 °Faverage high, July
Winter low−15 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights248nights a year at 32 °F or less
Growing degree days531base 50 °F — the season’s usable heat
Longest day20 h 08 mindaylight on June 21
Shortest day4 h 51 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation11.8 inper year, rain and melted snow
Snowfall55 inper year

Average high and low, by month

−30°−20°−10°0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 5 °F, low -15 °F 5°−15° JanFebruary: average high 16 °F, low -9 °F 16°−9° FebMarch: average high 27 °F, low -6 °F 27°−6° MarApril: average high 43 °F, low 13 °F 43°13° AprMay: average high 56 °F, low 30 °F 56°30° MayJune: average high 66 °F, low 43 °F 66°43° JunJuly: average high 69 °F, low 47 °F 69°47° JulAugust: average high 63 °F, low 42 °F 63°42° AugSeptember: average high 53 °F, low 33 °F 53°33° SepOctober: average high 35 °F, low 18 °F 35°18° OctNovember: average high 16 °F, low -4 °F 16°−4° NovDecember: average high 5 °F, low -13 °F 5°−13° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.47 in precipitation, 7.6 in snowfall 0.5❄8 JanFebruary: 0.55 in precipitation, 6.7 in snowfall 0.6❄7 FebMarch: 0.37 in precipitation, 4.7 in snowfall 0.4❄5 MarApril: 0.16 in precipitation, 2.6 in snowfall 0.2❄3 AprMay: 0.73 in precipitation, 2.6 in snowfall 0.7❄3 MayJune: 1.82 in precipitation 1.8 JunJuly: 2.38 in precipitation 2.4 JulAugust: 1.78 in precipitation 1.8 AugSeptember: 1.28 in precipitation, 2.7 in snowfall 1.3❄3 SepOctober: 0.98 in precipitation, 9.7 in snowfall 1.0❄10 OctNovember: 0.61 in precipitation, 8.5 in snowfall 0.6❄9 NovDecember: 0.63 in precipitation, 9.4 in snowfall 0.6❄9 Dec

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

Nearby ZIP codes

7 of the 7 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

997294a
Cantwell, AK · 54 mi
997373a
Delta Junction, AK · 68 mi
995734b
Copper Center, AK · 86 mi
997312a
Fort Greely, AK · 86 mi
996744b
Sutton, AK · 88 mi
995745a
Cordova, AK · 114 mi
996865a
Valdez, AK · 116 mi

Alaska planting zones →

Questions about 99588

What planting zone is ZIP code 99588?

ZIP code 99588 (Glennallen, AK) is in USDA hardiness zone 2b on the 2023 map: the coldest night of an average winter reaches −45 to −40 °F (−42.8 to −40 °C).

When is the last frost in Glennallen, AK?

The median last spring frost (32 °F) near 99588 is May 30; after June 9 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lake Susitna station.

When is the first frost in Glennallen, AK?

The median first fall frost near 99588 is September 4, giving a median frost-free growing season of 95 days.

When should I plant tomatoes in 99588?

Start tomato seeds indoors around Apr 4 – Apr 18 and set transplants outside around Jun 6 – Jun 20, one to three weeks after the median last frost.

How much rain and snow does 99588 get?

About 11.8 inches of precipitation a year and 55 inches of snowfall (NOAA 1991–2020 normals, Lake Susitna station).

How hot do summers get in Glennallen, AK?

The average high peaks at 69 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99588 have?

The USDA soil survey maps Klasi at the center of ZIP 99588: peat, poorly drained, pH about 5.8 (moderately acidic).

What kind of onions grow in Glennallen, AK?

Long-day onions: the longest day near 99588 is 20 h 08 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99588 change?

Yes. The 2012 USDA map put 99588 in zone 2a; the 2023 map puts it in zone 2b. The newer map uses 1991–2020 data and more weather stations.