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

Planting zone for 99503 — Anchorage, AK

ZIP code 99503 (Anchorage, Anchorage Municipality) is in USDA zone 3a: the coldest winter night averages −40 to −35 °F.

Where ZIP 99503 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.

Zone3a−40 to −35 °F
Coldest night−40 to −37.2 °C
Last frostrare
First frostrare
2012 zone4b

Was 4b on the 2012 map — 1.5 zones colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 3a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Anchorage, 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

No NOAA station with frost records lies within 90 miles of Anchorage, AK, so we don't show frost dates here rather than guess. Your local extension office can give you a date.

Native plants for zone 3a in Alaska

80 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −40 °F or colder — the bottom of zone 3a. 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 26

alpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °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 °Fchokecherry25 ft · blooms mid spring · high shade tolerance · to −43 °Fcommon juniper10 ft · blooms mid spring · high shade tolerance · to −43 °F

Wildflowers & perennials 22

alpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °Falpine 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 °F

Grasses 19

alpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Farctic bluegrass2 ft · high shade tolerance · to −62 °FBigelow's sedge0.4 ft · blooms mid summer · medium shade tolerance · to −43 °Fglaucous bluegrass2 ft · blooms mid summer · high shade tolerance · to −40 °Fhair-like sedge1.7 ft · blooms late spring · low shade tolerance · to −43 °FHoppner'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 Anchorage, AK.

Soil in Anchorage, AK

The soil mapped at the center of ZIP 99503 is 30-Subalpine woodland, gravelly colluvial slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer
pH4.0strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter90%high
Hydrologic groupBwater soaks in moderately
Farmland classNot prime farmlandUSDA classification

Map unit: Yukon-Kuskokwim Highlands, Boreal and Subalpine Mountains.

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 99503; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Anchorage, AK

Longest day19 h 46 mindaylight on June 21
Shortest day5 h 08 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Daylight is calculated from latitude.

Nearby ZIP codes

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

995753a
Crooked Creek, AK · 17 mi
996563a
Red Devil, AK · 29 mi
996682b
Sleetmute, AK · 44 mi
996653a
Shageluk, AK · 63 mi

All 25 ZIP codes in Anchorage → · Alaska planting zones →

Questions about 99503

What planting zone is ZIP code 99503?

ZIP code 99503 (Anchorage, AK) is in USDA hardiness zone 3a on the 2023 map: the coldest night of an average winter reaches −40 to −35 °F (−40 to −37.2 °C).

What kind of soil does 99503 have?

The USDA soil survey maps 30-Subalpine woodland, gravelly colluvial slopes at the center of ZIP 99503: slightly decomposed plant material, well drained, pH about 4.0 (strongly acidic).

What kind of onions grow in Anchorage, AK?

Long-day onions: the longest day near 99503 is 19 h 46 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99503 change?

Yes. The 2012 USDA map put 99503 in zone 4b; the 2023 map puts it in zone 3a. The newer map uses 1991–2020 data and more weather stations.