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

Planting zone for 99729 — Cantwell, AK

ZIP code 99729 (Cantwell, Denali County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is June 6 and the first fall frost August 25.

Where ZIP 99729 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.

Zone4a−30 to −25 °F

Coldest night−34.4 to −31.7 °C

Last frostJun 6

First frostAug 25

2012 zone2b

Was 2b 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 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Cantwell, 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 Cantwell, AK

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 6median — 50% chance of a later frost

Safe for tender plantsJune 30only 10% chance of frost after

First fall frostAugust 25median — 10% chance by Aug 9

Growing season77 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 21 and returns around September 6.

From the NOAA station Mckinley Park, AK — 45 miles away, elevation 2,070 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 99729

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 25 – May 9

SpinachSow outdoors · Apr 25 – May 16

Broccoli, cabbageStart indoors · Mar 28 – Apr 11

Broccoli, cabbageTransplant · May 16 – May 30

Onion setsPlant outdoors · May 9 – May 23

PotatoesPlant outdoors · May 16 – May 30

LettuceSow outdoors · May 9 – May 23

Carrots, beetsSow outdoors · May 16 – May 30

TomatoesStart indoors · Apr 11 – Apr 25

TomatoesTransplant · Jun 13 – Jun 27

Peppers, eggplantStart indoors · Mar 28 – Apr 11

Peppers, eggplantTransplant · Jun 20 – Jul 4

BeansSow outdoors · Jun 13 – Jun 27

Sweet cornSow outdoors · Jun 13 – Jun 27

Cucumbers, squashSow outdoors · Jun 13 – Jun 27

Fall lettuce, spinachSow outdoors · Jun 30 – Jul 14

GarlicPlant cloves · Aug 11 – Sep 15

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 6) and first fall frost (Aug 25) 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 4a in Alaska

240 plants native to Alaska, recorded in Alaska, and rated by the USDA to survive −30 °F or colder — the bottom of zone 4a. 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 Cantwell, AK.

Soil in Cantwell, AK

The soil mapped at the center of ZIP 99729 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-Rounded 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 99729; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Cantwell, AK

Summer high66 °Faverage high, July

Winter low−9 °Faverage low, January

Hot days0days a year at 90 °F or more

Freezing nights260nights a year at 32 °F or less

Growing degree days348base 50 °F — the season’s usable heat

Longest day20 h 28 mindaylight on June 21

Shortest day4 h 35 mindaylight on December 21

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

Precipitation21.5 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: Cantwell 2 E, AK (30 mi away); precipitation: Monahan Flat, AK (11 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.

997553b

Denali National Park, AK · 52 mi

995882b

Glennallen, AK · 54 mi

997312a

Fort Greely, AK · 68 mi

Eielson Afb, AK · 101 mi

Alaska planting zones →

Questions about 99729

What planting zone is ZIP code 99729?

ZIP code 99729 (Cantwell, AK) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Cantwell, AK?

The median last spring frost (32 °F) near 99729 is June 6; after June 30 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mckinley Park station.

When is the first frost in Cantwell, AK?

The median first fall frost near 99729 is August 25, giving a median frost-free growing season of 77 days.

When should I plant tomatoes in 99729?

Start tomato seeds indoors around Apr 11 – Apr 25 and set transplants outside around Jun 13 – Jun 27, one to three weeks after the median last frost.

How much rain and snow does 99729 get?

About 21.5 inches of precipitation a year (NOAA 1991–2020 normals, Monahan Flat station).

How hot do summers get in Cantwell, 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 99729 have?

The USDA soil survey maps E28-boreal alpine dwarf scrub-gravelly colluvial slopes at the center of ZIP 99729: slightly decomposed plant material, well drained.

What kind of onions grow in Cantwell, AK?

Long-day onions: the longest day near 99729 is 20 h 28 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99729 change?

Yes. The 2012 USDA map put 99729 in zone 2b; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.