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

Planting zone for 99606 — Iliamna, AK

ZIP code 99606 (Iliamna, Lake and Peninsula County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 10 and the first fall frost October 1.

Where ZIP 99606 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.

Zone4b−25 to −20 °F
Coldest night−31.7 to −28.9 °C
Last frostMay 10
First frostOct 1
2012 zone4b

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 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Iliamna, 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 Iliamna, AK

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 10median — 50% chance of a later frost
Safe for tender plantsMay 25only 10% chance of frost after
First fall frostOctober 1median — 10% chance by Sep 17
Growing season144 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 28 and returns around October 10.

From the NOAA station Iliamna Airport, AK — within 1 mile, elevation 144 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 99606

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 29 – Apr 12
SpinachSow outdoors · Mar 29 – Apr 19
Broccoli, cabbageStart indoors · Mar 1 – Mar 15
Broccoli, cabbageTransplant · Apr 19 – May 3
Onion setsPlant outdoors · Apr 12 – Apr 26
PotatoesPlant outdoors · Apr 19 – May 3
LettuceSow outdoors · Apr 12 – Apr 26
Carrots, beetsSow outdoors · Apr 19 – May 3
TomatoesStart indoors · Mar 15 – Mar 29
TomatoesTransplant · May 17 – May 31
Peppers, eggplantStart indoors · Mar 1 – Mar 15
Peppers, eggplantTransplant · May 24 – Jun 7
BeansSow outdoors · May 17 – May 31
Sweet cornSow outdoors · May 17 – May 31
Cucumbers, squashSow outdoors · May 17 – May 31
Fall lettuce, spinachSow outdoors · Aug 6 – Aug 20
GarlicPlant cloves · Sep 17 – Oct 22
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 10) and first fall frost (Oct 1) 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 4b in Alaska

260 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Trees 11

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 °FPacific silver fir165 ft · blooms late spring · low shade tolerance · to −28 °Fpaper birch70 ft · blooms mid spring · high shade tolerance · to −62 °Fquaking aspen65 ft · blooms mid spring · high shade tolerance · to −70 °F

Shrubs 44

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 112

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 84

Alaska 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 °Fbeaked sedge4 ft · blooms late 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 Iliamna, AK.

Soil in Iliamna, AK

The soil mapped at the center of ZIP 99606 is E36-boreal forest and woodland-silty till slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH4.4strongly 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: Bristol Bay-Northern Alaska Peninsula Lowlands-Boreal and Northwest Maritimel-Glaciated Plains, Ash Influenced.

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 99606; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Iliamna, AK

Summer high65 °Faverage high, July
Winter low12 °Faverage low, January
Hot days0days a year at 90 °F or more
Freezing nights170nights a year at 32 °F or less
Growing degree days655base 50 °F — the season’s usable heat
Longest day18 h 46 mindaylight on June 21
Shortest day5 h 57 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation25 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°32 °FJanuary: average high 25 °F, low 12 °F 25°12° JanFebruary: average high 30 °F, low 16 °F 30°16° FebMarch: average high 32 °F, low 16 °F 32°16° MarApril: average high 43 °F, low 29 °F 43°29° AprMay: average high 55 °F, low 38 °F 55°38° MayJune: average high 62 °F, low 45 °F 62°45° JunJuly: average high 65 °F, low 51 °F 65°51° JulAugust: average high 64 °F, low 50 °F 64°50° AugSeptember: average high 56 °F, low 43 °F 56°43° SepOctober: average high 45 °F, low 32 °F 45°32° OctNovember: average high 33 °F, low 21 °F 33°21° NovDecember: average high 28 °F, low 15 °F 28°15° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 0.90 in precipitation 0.9 JanFebruary: 1.06 in precipitation 1.1 FebMarch: 0.84 in precipitation 0.8 MarApril: 0.83 in precipitation 0.8 AprMay: 1.19 in precipitation 1.2 MayJune: 1.51 in precipitation 1.5 JunJuly: 3.08 in precipitation 3.1 JulAugust: 4.14 in precipitation 4.1 AugSeptember: 5.01 in precipitation 5.0 SepOctober: 2.84 in precipitation 2.8 OctNovember: 2.16 in precipitation 2.2 NovDecember: 1.45 in precipitation 1.4 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Iliamna Airport, AK (within 1 mile); precipitation: Iliamna Airport, AK (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

3 of the 4 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

996474b
Pedro Bay, AK · 31 mi
996534a
Port Alsworth, AK · 35 mi
996134a
King Salmon, AK · 49 mi
996404a
Nondalton, AK · 72 mi

Alaska planting zones →

Questions about 99606

What planting zone is ZIP code 99606?

ZIP code 99606 (Iliamna, AK) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Iliamna, AK?

The median last spring frost (32 °F) near 99606 is May 10; after May 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Iliamna Airport station.

When is the first frost in Iliamna, AK?

The median first fall frost near 99606 is October 1, giving a median frost-free growing season of 144 days.

When should I plant tomatoes in 99606?

Start tomato seeds indoors around Mar 15 – Mar 29 and set transplants outside around May 17 – May 31, one to three weeks after the median last frost.

How much rain and snow does 99606 get?

About 25 inches of precipitation a year (NOAA 1991–2020 normals, Iliamna Airport station).

How hot do summers get in Iliamna, AK?

The average high peaks at 65 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99606 have?

The USDA soil survey maps E36-boreal forest and woodland-silty till slopes at the center of ZIP 99606: slightly decomposed plant material, well drained, pH about 4.4 (strongly acidic).

What kind of onions grow in Iliamna, AK?

Long-day onions: the longest day near 99606 is 18 h 46 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).