Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 99573 — Copper Center, AK

ZIP code 99573 (Copper Center, Copper River Census Area County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is April 30 and the first fall frost October 2.

Where ZIP 99573 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 frostApr 30

First frostOct 2

2012 zone2a

Was 2a on the 2012 map — 2.5 zones warmer now. 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 Copper Center, 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 Copper Center, AK

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostApril 30median — 50% chance of a later frost

Safe for tender plantsMay 10only 10% chance of frost after

First fall frostOctober 2median — 10% chance by Sep 20

Growing season157 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 14 and returns around October 20.

From the NOAA station Valdez WSO, AK — 38 miles away, elevation 95 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 99573

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 19 – Apr 2

SpinachSow outdoors · Mar 19 – Apr 9

Broccoli, cabbageStart indoors · Feb 19 – Mar 5

Broccoli, cabbageTransplant · Apr 9 – Apr 23

Onion setsPlant outdoors · Apr 2 – Apr 16

PotatoesPlant outdoors · Apr 9 – Apr 23

LettuceSow outdoors · Apr 2 – Apr 16

Carrots, beetsSow outdoors · Apr 9 – Apr 23

TomatoesStart indoors · Mar 5 – Mar 19

TomatoesTransplant · May 7 – May 21

Peppers, eggplantStart indoors · Feb 19 – Mar 5

Peppers, eggplantTransplant · May 14 – May 28

BeansSow outdoors · May 7 – May 21

Sweet cornSow outdoors · May 7 – May 21

Cucumbers, squashSow outdoors · May 7 – May 21

Fall lettuce, spinachSow outdoors · Aug 7 – Aug 21

GarlicPlant cloves · Sep 18 – Oct 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 30) and first fall frost (Oct 2) 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.

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 Copper Center, AK.

Soil in Copper Center, AK

The soil mapped at the center of ZIP 99573 is E28-boreal forest-gravelly colluvial slopes — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

DrainageWell drainednatural drainage class

Organic matter75%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Interior Alaska Mountains-Boreal Upland and Lowland-Mountain 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 99573; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Copper Center, AK

Summer high70 °Faverage high, July

Winter low−9 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights259nights a year at 32 °F or less

Growing degree days476base 50 °F — the season’s usable heat

Longest day19 h 32 mindaylight on June 21

Shortest day5 h 19 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation13.3 inper year, rain and melted snow

Snowfall72 inper year; 201 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

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

Nearby ZIP codes

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

Glennallen, AK · 86 mi

995862b

Gakona, AK · 90 mi

Alaska planting zones →

Questions about 99573

What planting zone is ZIP code 99573?

ZIP code 99573 (Copper Center, 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 Copper Center, AK?

The median last spring frost (32 °F) near 99573 is April 30; after May 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Valdez WSO station.

When is the first frost in Copper Center, AK?

The median first fall frost near 99573 is October 2, giving a median frost-free growing season of 157 days.

When should I plant tomatoes in 99573?

Start tomato seeds indoors around Mar 5 – Mar 19 and set transplants outside around May 7 – May 21, one to three weeks after the median last frost.

How much rain and snow does 99573 get?

About 13.3 inches of precipitation a year and 72 inches of snowfall (NOAA 1991–2020 normals, Tonsina station).

How hot do summers get in Copper Center, AK?

The average high peaks at 70 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99573 have?

The USDA soil survey maps E28-boreal forest-gravelly colluvial slopes at the center of ZIP 99573: slightly decomposed plant material, well drained.

What kind of onions grow in Copper Center, AK?

Long-day onions: the longest day near 99573 is 19 h 32 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99573 change?

Yes. The 2012 USDA map put 99573 in zone 2a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.