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

Planting zone for 99688 — Willow, AK

ZIP code 99688 (Willow, Matanuska-Susitna Borough) is in USDA zone 3b: the coldest winter night averages −35 to −30 °F. The median last spring frost is May 15 and the first fall frost September 18.

Where ZIP 99688 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.

Zone3b−35 to −30 °F

Coldest night−37.2 to −34.4 °C

Last frostMay 15

First frostSep 18

2012 zone3a

Was 3a 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 3b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Willow, 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 Willow, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 15median — 50% chance of a later frost

Safe for tender plantsMay 28only 10% chance of frost after

First fall frostSeptember 18median — 10% chance by Sep 4

Growing season126 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around September 27.

From the NOAA station Willow West, AK — 17 miles away, elevation 207 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 99688

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 3 – Apr 17

SpinachSow outdoors · Apr 3 – Apr 24

Broccoli, cabbageStart indoors · Mar 6 – Mar 20

Broccoli, cabbageTransplant · Apr 24 – May 8

Onion setsPlant outdoors · Apr 17 – May 1

PotatoesPlant outdoors · Apr 24 – May 8

LettuceSow outdoors · Apr 17 – May 1

Carrots, beetsSow outdoors · Apr 24 – May 8

TomatoesStart indoors · Mar 20 – Apr 3

TomatoesTransplant · May 22 – Jun 5

Peppers, eggplantStart indoors · Mar 6 – Mar 20

Peppers, eggplantTransplant · May 29 – Jun 12

BeansSow outdoors · May 22 – Jun 5

Sweet cornSow outdoors · May 22 – Jun 5

Cucumbers, squashSow outdoors · May 22 – Jun 5

Fall lettuce, spinachSow outdoors · Jul 24 – Aug 7

GarlicPlant cloves · Sep 4 – Oct 9

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 15) and first fall frost (Sep 18) 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 3b in Alaska

172 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −35 °F or colder — the bottom of zone 3b. 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 Willow, AK.

Soil in Willow, AK

The soil mapped at the center of ZIP 99688 is Cryods — slightly decomposed plant material, somewhat poorly drained.

TextureSlightly decomposed plant materialtop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageSomewhat poorly drainedconsider raised beds

Organic matter60%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Cryods and Cryaquepts, cool, 0 to 35 percent slopes.

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 99688; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Willow, AK

Summer high68 °Faverage high, July

Winter low−4 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights219nights a year at 32 °F or less

Growing degree days808base 50 °F — the season’s usable heat

Longest day19 h 42 mindaylight on June 21

Shortest day5 h 11 mindaylight on December 21

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

Precipitation42.4 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: Willow West, AK (17 mi away); precipitation: Independence Mine, AK (13 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 99688

What planting zone is ZIP code 99688?

ZIP code 99688 (Willow, AK) is in USDA hardiness zone 3b on the 2023 map: the coldest night of an average winter reaches −35 to −30 °F (−37.2 to −34.4 °C).

When is the last frost in Willow, AK?

The median last spring frost (32 °F) near 99688 is May 15; after May 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Willow West station.

When is the first frost in Willow, AK?

The median first fall frost near 99688 is September 18, giving a median frost-free growing season of 126 days.

When should I plant tomatoes in 99688?

Start tomato seeds indoors around Mar 20 – Apr 3 and set transplants outside around May 22 – Jun 5, one to three weeks after the median last frost.

How much rain and snow does 99688 get?

About 42.4 inches of precipitation a year (NOAA 1991–2020 normals, Independence Mine station).

How hot do summers get in Willow, AK?

The average high peaks at 68 °F in July, with about 0 days a year at 90 °F or more.

What kind of soil does 99688 have?

The USDA soil survey maps Cryods at the center of ZIP 99688: slightly decomposed plant material, somewhat poorly drained, pH about 5.0 (strongly acidic).

What kind of onions grow in Willow, AK?

Long-day onions: the longest day near 99688 is 19 h 42 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99688 change?

Yes. The 2012 USDA map put 99688 in zone 3a; the 2023 map puts it in zone 3b. The newer map uses 1991–2020 data and more weather stations.