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

Planting zone for 99840 — Skagway, AK

ZIP code 99840 (Skagway, Skagway County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is April 21 and the first fall frost October 17.

Where ZIP 99840 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 frostApr 21

First frostOct 17

2012 zone6a

Was 6a on the 2012 map — a full zone colder 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 Skagway, 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 Skagway, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 21median — 50% chance of a later frost

Safe for tender plantsMay 2only 10% chance of frost after

First fall frostOctober 17median — 10% chance by Oct 1

Growing season176 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 5 and returns around November 2.

From the NOAA station Skagway Airport, AK — 7 miles away, elevation 20 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 99840

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 10 – Mar 24

SpinachSow outdoors · Mar 10 – Mar 31

Broccoli, cabbageStart indoors · Feb 10 – Feb 24

Broccoli, cabbageTransplant · Mar 31 – Apr 14

Onion setsPlant outdoors · Mar 24 – Apr 7

PotatoesPlant outdoors · Mar 31 – Apr 14

LettuceSow outdoors · Mar 24 – Apr 7

Carrots, beetsSow outdoors · Mar 31 – Apr 14

TomatoesStart indoors · Feb 24 – Mar 10

TomatoesTransplant · Apr 28 – May 12

Peppers, eggplantStart indoors · Feb 10 – Feb 24

Peppers, eggplantTransplant · May 5 – May 19

BeansSow outdoors · Apr 28 – May 12

Sweet cornSow outdoors · Apr 28 – May 12

Cucumbers, squashSow outdoors · Apr 28 – May 12

Fall lettuce, spinachSow outdoors · Aug 22 – Sep 5

GarlicPlant cloves · Oct 3 – Nov 7

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 21) and first fall frost (Oct 17) 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 Skagway, AK.

Soil in Skagway, AK

The soil mapped at the center of ZIP 99840 is 22-Maritime Forest Gravelly Floodplains — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH5.8moderately acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter80%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Maritime Floodplains, Gravelly.

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 99840; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Skagway, AK

Summer high65 °Faverage high, July

Winter low22 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights125nights a year at 32 °F or less

Growing degree days815base 50 °F — the season’s usable heat

Longest day18 h 42 mindaylight on June 21

Shortest day6 h 00 mindaylight on December 21

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

Precipitation46.8 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Skagway Airport, AK (7 mi away); precipitation: Moore Creek Bridge, AK (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Alaska planting zones →

Questions about 99840

What planting zone is ZIP code 99840?

ZIP code 99840 (Skagway, 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 Skagway, AK?

The median last spring frost (32 °F) near 99840 is April 21; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Skagway Airport station.

When is the first frost in Skagway, AK?

The median first fall frost near 99840 is October 17, giving a median frost-free growing season of 176 days.

When should I plant tomatoes in 99840?

Start tomato seeds indoors around Feb 24 – Mar 10 and set transplants outside around Apr 28 – May 12, one to three weeks after the median last frost.

How much rain and snow does 99840 get?

About 46.8 inches of precipitation a year (NOAA 1991–2020 normals, Moore Creek Bridge station).

How hot do summers get in Skagway, 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 99840 have?

The USDA soil survey maps 22-Maritime Forest Gravelly Floodplains at the center of ZIP 99840: slightly decomposed plant material, well drained, pH about 5.8 (moderately acidic).

What kind of onions grow in Skagway, AK?

Long-day onions: the longest day near 99840 is 18 h 42 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99840 change?

Yes. The 2012 USDA map put 99840 in zone 6a; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.