What does USDA hardiness zone 1b mean in Alaska?

Zone 1b means an average annual extreme minimum winter temperature of −55 to −50 °F — the standard USDA measure of which perennials survive winter. 7 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 1b is the growing season longest?

Galena runs the longest season on this page at about 111 days; Tanacross is shortest at about 79 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 1b?

Using Arctic's frost dates (this page's median-season location): start seeds indoors about Mar 30 – Apr 13, then transplant outside about Jun 1 – Jun 8. 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 1b 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 7 locations listed (see the table above for each location's own dates).

USDA zone 1b in Alaska

−55 to −50 °F avg. annual extreme minimum · 7 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 1b covers 7 locations across Alaska (average annual extreme minimum −55 to −50 °F): Arctic, AK, Chicken, AK, Galena, AK, Kobuk, AK, Rampart, AK, Shungnak, AK, and 1 more. Average last spring frost across this group ranges May 18 (Galena) to June 5 (Shungnak), and growing seasons run 79–111 days (Tanacross to Galena) — 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 Arctic, this group's median-season location.

USDA zone: 1b−55 to −50 °F
Last frost range: May 18–Jun 5avg, 32°F
First frost range: Aug 23–Sep 24avg, 32°F
Growing season range: 79–111days

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)
Arctic *	—	Central #2	May 25	Aug 26	92
Chicken	—	Eagle	May 29	Aug 23	86
Galena	—	Galena	May 18	Sep 8	111
Kobuk	Bettles	Bettles Ap	May 22	Aug 24	94
Rampart	Manley Hot Springs, Tanana, Hughes	Tanana Calhoun Mem Ap	May 29	Aug 28	89
Shungnak	—	Kotzebue Ralph Wein Ap	Jun 5	Sep 24	110
Tanacross	—	Tok #2	Jun 3	Aug 27	79

* Arctic 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 (Arctic, representative)

Computed from Arctic's average frost dates — the median-season location in this Alaskazone 1b 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 Arctic (Alaska, zone 1b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 30 – Apr 13	Jun 1 – Jun 8	Jul 31 – Aug 20	—	matures, but with little margin
Pepper	Very tender	Mar 16 – Mar 30	Jun 8 – Jun 15	Aug 7 – Sep 6	—	needs season extension (cold frame, row cover, or transplants) to mature
Cucumber	Tender	Apr 27 – May 4	Jun 1 – Jun 8	Jul 21 – Aug 10	—	matures comfortably
Summer squash / zucchini	Tender	—	Jun 1 – Jun 8	Jul 16 – Jul 31	—	matures comfortably
Bush bean	Tender	—	Jun 1 – Jun 8	Jul 21 – Jul 31	Jun 27 – Jul 7	matures comfortably
Sweet corn	Tender	—	May 25 – Jun 8	Jul 24 – Aug 23	—	matures, but with little margin
Basil	Very tender	Apr 13 – Apr 27	Jun 1 – Jun 8	Jul 1 – Jul 16	—	matures comfortably
Lettuce	Half-hardy	Apr 13 – Apr 27	Apr 27 – May 11	Jun 11 – Jun 26	Jun 13 – Jun 28	matures comfortably
Pea	Hardy	—	Apr 13 – Apr 27	Jun 7 – Jun 22	Jun 3 – Jun 18	matures comfortably
Spinach	Hardy	—	Apr 13 – Apr 27	May 23 – Jun 2	Jun 23 – Jul 3	matures comfortably
Carrot	Half-hardy	—	May 4 – May 11	Jul 3 – Jul 23	May 24 – Jun 13	matures comfortably
Broccoli	Half-hardy	Mar 30 – Apr 13	Apr 27 – May 11	Jun 21 – Jul 11	May 29 – Jun 18	matures comfortably

Which crops fit this growing season

Using Arctic's own 92-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 9 of 12 crops mature here with comfortable margin, 2mature with little room to spare, and 1 needs season extension (starting indoors earlier, a cold frame, or row cover) to reliably reach harvest before the first fall frost. The tightest fits: tomato (+6 day margin), pepper (-11 day margin), sweet corn (+3 day 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 (Arctic)

From NOAA's 1991–2020 Climate Normals at station USC00501466. 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), Arctic.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	—	—	—	—	66
32°F (freeze)	May 25	Jun 6	Aug 26	Sep 7	92
28°F	May 14	May 28	Sep 5	Sep 18	113
24°F	May 7	May 20	Sep 16	Sep 28	131

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 7 locations is 754; Arctic's own reading is shown below.

Annual growing degree days for Arctic (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	859	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	2,060	cool-season crops (brassicas, greens)

Hardiness zone 1b in Alaska

Zone 1b means an average annual extreme minimum winter temperature of about −55 to −50 °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, 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b.

Explore zone 1b in other states at zone 1b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 1b mean in Alaska?: Zone 1b means an average annual extreme minimum winter temperature of −55 to −50 °F — the standard USDA measure of which perennials survive winter. 7 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 1b is the growing season longest?: Galena runs the longest season on this page at about 111 days; Tanacross is shortest at about 79 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 1b?: Using Arctic's frost dates (this page's median-season location): start seeds indoors about Mar 30 – Apr 13, then transplant outside about Jun 1 – Jun 8. 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 1b 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 7 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.