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

Planting zone for 99645 — Palmer, AK

ZIP code 99645 (Palmer, Matanuska-Susitna Borough) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 22 and the first fall frost September 16.

Where ZIP 99645 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.

Zone5a−20 to −15 °F

Coldest night−28.9 to −26.1 °C

Last frostMay 22

First frostSep 16

2012 zone4b

Was 4b 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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Palmer, 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 Palmer, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 22median — 50% chance of a later frost

Safe for tender plantsJune 3only 10% chance of frost after

First fall frostSeptember 16median — 10% chance by Sep 1

Growing season114 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 6 and returns around September 28.

From the NOAA station Lazy Mtn, AK — 2 miles away, elevation 732 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 99645

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 10 – Apr 24

SpinachSow outdoors · Apr 10 – May 1

Broccoli, cabbageStart indoors · Mar 13 – Mar 27

Broccoli, cabbageTransplant · May 1 – May 15

Onion setsPlant outdoors · Apr 24 – May 8

PotatoesPlant outdoors · May 1 – May 15

LettuceSow outdoors · Apr 24 – May 8

Carrots, beetsSow outdoors · May 1 – May 15

TomatoesStart indoors · Mar 27 – Apr 10

TomatoesTransplant · May 29 – Jun 12

Peppers, eggplantStart indoors · Mar 13 – Mar 27

Peppers, eggplantTransplant · Jun 5 – Jun 19

BeansSow outdoors · May 29 – Jun 12

Sweet cornSow outdoors · May 29 – Jun 12

Cucumbers, squashSow outdoors · May 29 – Jun 12

Fall lettuce, spinachSow outdoors · Jul 22 – Aug 5

GarlicPlant cloves · Sep 2 – Oct 7

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 22) and first fall frost (Sep 16) 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 5a in Alaska

275 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. 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 Palmer, AK.

Soil in Palmer, AK

The soil mapped at the center of ZIP 99645 is E23-boreal alpine scrub-gravelly colluvial slopes — moderately decomposed plant material, well drained.

TextureModerately 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 Alpine-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 99645; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Palmer, AK

Summer high66 °Faverage high, July

Winter low9 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights218nights a year at 32 °F or less

Growing degree days510base 50 °F — the season’s usable heat

Longest day19 h 34 mindaylight on June 21

Shortest day5 h 18 mindaylight on December 21

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

Precipitation18 inper year, rain and melted snow

Snowfall83 inper year; 171 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: Lazy Mtn, AK (2 mi away); precipitation: Lazy Mtn, AK (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

2 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

Eagle River, AK · 33 mi

Alaska planting zones →

Questions about 99645

What planting zone is ZIP code 99645?

ZIP code 99645 (Palmer, AK) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Palmer, AK?

The median last spring frost (32 °F) near 99645 is May 22; after June 3 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lazy Mtn station.

When is the first frost in Palmer, AK?

The median first fall frost near 99645 is September 16, giving a median frost-free growing season of 114 days.

When should I plant tomatoes in 99645?

Start tomato seeds indoors around Mar 27 – Apr 10 and set transplants outside around May 29 – Jun 12, one to three weeks after the median last frost.

How much rain and snow does 99645 get?

About 18 inches of precipitation a year and 83 inches of snowfall (NOAA 1991–2020 normals, Lazy Mtn station).

How hot do summers get in Palmer, AK?

The average high peaks at 66 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99645 have?

The USDA soil survey maps E23-boreal alpine scrub-gravelly colluvial slopes at the center of ZIP 99645: moderately decomposed plant material, well drained, pH about 5.0 (strongly acidic).

What kind of onions grow in Palmer, AK?

Long-day onions: the longest day near 99645 is 19 h 34 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99645 change?

Yes. The 2012 USDA map put 99645 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.