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

Planting zone for 99737 — Delta Junction, AK

ZIP code 99737 (Delta Junction, Southeast Fairbanks Census Area County) is in USDA zone 3a: the coldest winter night averages −40 to −35 °F. The median last spring frost is May 30 and the first fall frost August 24.

Where ZIP 99737 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 frostMay 30

First frostAug 24

2012 zone1b

Was 1b on the 2012 map — 1.5 zones warmer 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 Delta Junction, 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 Delta Junction, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

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

Safe for tender plantsJune 13only 10% chance of frost after

First fall frostAugust 24median — 10% chance by Aug 9

Growing season84 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 18 and returns around September 3.

From the NOAA station Dry Creek, AK — 27 miles away, elevation 1,355 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 99737

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 18 – May 2

SpinachSow outdoors · Apr 18 – May 9

Broccoli, cabbageStart indoors · Mar 21 – Apr 4

Broccoli, cabbageTransplant · May 9 – May 23

Onion setsPlant outdoors · May 2 – May 16

PotatoesPlant outdoors · May 9 – May 23

LettuceSow outdoors · May 2 – May 16

Carrots, beetsSow outdoors · May 9 – May 23

TomatoesStart indoors · Apr 4 – Apr 18

TomatoesTransplant · Jun 6 – Jun 20

Peppers, eggplantStart indoors · Mar 21 – Apr 4

Peppers, eggplantTransplant · Jun 13 – Jun 27

BeansSow outdoors · Jun 6 – Jun 20

Sweet cornSow outdoors · Jun 6 – Jun 20

Cucumbers, squashSow outdoors · Jun 6 – Jun 20

Fall lettuce, spinachSow outdoors · Jun 29 – Jul 13

GarlicPlant cloves · Aug 10 – Sep 14

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 30) and first fall frost (Aug 24) 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.

Soil in Delta Junction, AK

The soil mapped at the center of ZIP 99737 is E28-boreal alpine dwarf scrub-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 Alpine-Barren 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 99737; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Delta Junction, AK

Summer high72 °Faverage high, July

Winter low−15 °Faverage low, January

Hot days1days a year at 90 °F or more

Freezing nights246nights a year at 32 °F or less

Growing degree days782base 50 °F — the season’s usable heat

Longest day20 h 36 mindaylight on June 21

Shortest day4 h 30 mindaylight on December 21

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

Precipitation21 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: Dry Creek, AK (27 mi away); precipitation: Fielding Lake, AK (20 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

6 of the 6 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

997063b

Fairbanks, AK · 43 mi

997312a

Fort Greely, AK · 50 mi

995862b

Gakona, AK · 62 mi

995882b

Glennallen, AK · 68 mi

997143b

Salcha, AK · 75 mi

997162a

Two Rivers, AK · 110 mi

Alaska planting zones →

Questions about 99737

What planting zone is ZIP code 99737?

ZIP code 99737 (Delta Junction, 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).

When is the last frost in Delta Junction, AK?

The median last spring frost (32 °F) near 99737 is May 30; after June 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Dry Creek station.

When is the first frost in Delta Junction, AK?

The median first fall frost near 99737 is August 24, giving a median frost-free growing season of 84 days.

When should I plant tomatoes in 99737?

Start tomato seeds indoors around Apr 4 – Apr 18 and set transplants outside around Jun 6 – Jun 20, one to three weeks after the median last frost.

How much rain and snow does 99737 get?

About 21 inches of precipitation a year (NOAA 1991–2020 normals, Fielding Lake station).

How hot do summers get in Delta Junction, AK?

The average high peaks at 72 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 99737 have?

The USDA soil survey maps E28-boreal alpine dwarf scrub-gravelly colluvial slopes at the center of ZIP 99737: slightly decomposed plant material, well drained.

What kind of onions grow in Delta Junction, AK?

Long-day onions: the longest day near 99737 is 20 h 36 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99737 change?

Yes. The 2012 USDA map put 99737 in zone 1b; the 2023 map puts it in zone 3a. The newer map uses 1991–2020 data and more weather stations.