What does USDA hardiness zone 7a mean in Alaska?

Zone 7a means an average annual extreme minimum winter temperature of 0 to 5 °F — the standard USDA measure of which perennials survive winter. 10 locations in Alaska fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Alaska's zone 7a is the growing season longest?

Elfin Cove runs the longest season on this page at about 188 days; Excursion Inlet is shortest at about 107 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in Alaska's zone 7a?

Using Karluk's frost dates (this page's median-season location): start seeds indoors about Mar 10 – Mar 24, then transplant outside about May 12 – May 19. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Alaska's zone 7a have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 10 locations listed (see the table above for each location's own dates).

USDA zone 7a in Alaska

0 to 5 °F avg. annual extreme minimum · 10 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 7a covers 10 locations across Alaska (average annual extreme minimum 0 to 5 °F): Angoon, AK, Cold Bay, AK, Elfin Cove, AK, Excursion Inlet, AK, Juneau city and, AK, Karluk, AK, and 4 more. Average last spring frost across this group ranges April 20 (Juneau city and) to May 31 (St. George), and growing seasons run 107–188 days (Excursion Inlet to Elfin Cove) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Alaska location's own frost dates; the printable planting calendar uses Karluk, this group's median-season location.

USDA zone: 7a0 to 5 °F
Last frost range: Apr 20–May 31avg, 32°F
First frost range: Sep 16–Nov 1avg, 32°F
Growing season range: 107–188days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Angoon	—	Hidden Falls Hatchery	Apr 29	Oct 25	176
Cold Bay	False Pass, King Cove	Cold Bay Ap	May 25	Oct 4	131
Elfin Cove	—	Elfin Cove	Apr 26	Nov 1	188
Excursion Inlet	Gustavus	Gustavus	May 30	Sep 16	107
Juneau city and	—	Juneau Dwtn	Apr 20	Oct 22	183
Karluk *	Port Lions	Kodiak Ap	May 5	Oct 3	151
Pelican	—	Pelican	May 4	Oct 19	167
St. George	—	St George Island Ap	May 31	Oct 5	128
Whitestone Logging Camp	Game Creek	Hoonah	May 9	Oct 4	145
Whittier	—	Wally Noerenberg Hatchery	May 20	Oct 9	142

* Karluk is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Karluk, representative)

Computed from Karluk's average frost dates — the median-season location in this Alaskazone 7a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Karluk (Alaska, zone 7a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 10 – Mar 24	May 12 – May 19	Jul 11 – Jul 31	—	matures comfortably
Pepper	Very tender	Feb 24 – Mar 10	May 19 – May 26	Jul 18 – Aug 17	—	matures comfortably
Cucumber	Tender	Apr 7 – Apr 14	May 12 – May 19	Jul 1 – Jul 21	—	matures comfortably
Summer squash / zucchini	Tender	—	May 12 – May 19	Jun 26 – Jul 11	—	matures comfortably
Bush bean	Tender	—	May 12 – May 19	Jul 1 – Jul 11	Aug 4 – Aug 14	matures comfortably
Sweet corn	Tender	—	May 5 – May 19	Jul 4 – Aug 3	—	matures comfortably
Basil	Very tender	Mar 24 – Apr 7	May 12 – May 19	Jun 11 – Jun 26	—	matures comfortably
Lettuce	Half-hardy	Mar 24 – Apr 7	Apr 7 – Apr 21	May 22 – Jun 6	Jul 21 – Aug 5	matures comfortably
Pea	Hardy	—	Mar 24 – Apr 7	May 18 – Jun 2	Jul 11 – Jul 26	matures comfortably
Spinach	Hardy	—	Mar 24 – Apr 7	May 3 – May 13	Jul 31 – Aug 10	matures comfortably
Carrot	Half-hardy	—	Apr 14 – Apr 21	Jun 13 – Jul 3	Jul 1 – Jul 21	matures comfortably
Broccoli	Half-hardy	Mar 10 – Mar 24	Apr 7 – Apr 21	Jun 1 – Jun 21	Jul 6 – Jul 26	matures comfortably

Which crops fit this growing season

Using Karluk's own 151-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Karluk)

From NOAA's 1991–2020 Climate Normals at station USW00025501. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Karluk.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 26	Jun 9	Sep 21	Oct 2	118
32°F (freeze)	May 5	May 21	Oct 3	Oct 17	151
28°F	Apr 18	May 3	Oct 17	Nov 5	185
24°F	Apr 4	Apr 20	Nov 3	Nov 23	212

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 10 locations is 491; Karluk's own reading is shown below.

Annual growing degree days for Karluk (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	551	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	2,048	cool-season crops (brassicas, greens)

Hardiness zone 7a in Alaska

Zone 7a means an average annual extreme minimum winter temperature of about 0 to 5 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Alaska spans 16 hardiness zones in this dataset — see all Alaska locations for the full range, including zones1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7b, 8a, 8b.

Explore zone 7a in other states at zone 7a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 7a mean in Alaska?: Zone 7a means an average annual extreme minimum winter temperature of 0 to 5 °F — the standard USDA measure of which perennials survive winter. 10 locations in Alaska fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Alaska's zone 7a is the growing season longest?: Elfin Cove runs the longest season on this page at about 188 days; Excursion Inlet is shortest at about 107 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in Alaska's zone 7a?: Using Karluk's frost dates (this page's median-season location): start seeds indoors about Mar 10 – Mar 24, then transplant outside about May 12 – May 19. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Alaska's zone 7a have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 10 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.