What does USDA hardiness zone 8b mean in Alaska?

Zone 8b means an average annual extreme minimum winter temperature of 15 to 20 °F — the standard USDA measure of which perennials survive winter. 2 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 8b is the growing season longest?

Nikolski runs the longest season on this page at about 164 days; Adak is shortest at about 128 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 8b?

Using Nikolski's frost dates (this page's median-season location): start seeds indoors about Mar 11 – Mar 25, then transplant outside about May 13 – May 20. 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 8b 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 2 locations listed (see the table above for each location's own dates).

USDA zone 8b in Alaska

15 to 20 °F avg. annual extreme minimum · 2 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 8b covers 2 locations across Alaska (average annual extreme minimum 15 to 20 °F): Adak, AK, Nikolski, AK. Average last spring frost across this group ranges May 6 (Nikolski) to May 31 (Adak), and growing seasons run 128–164 days (Adak to Nikolski) — 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 Nikolski, this group's median-season location.

USDA zone: 8b15 to 20 °F
Last frost range: May 6–May 31avg, 32°F
First frost range: Oct 5–Oct 18avg, 32°F
Growing season range: 128–164days

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)
Adak	—	St George Island Ap	May 31	Oct 5	128
Nikolski *	Unalaska, Atka	Dutch Harbor	May 6	Oct 18	164

* Nikolski 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 (Nikolski, representative)

Computed from Nikolski's average frost dates — the median-season location in this Alaskazone 8b 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 Nikolski (Alaska, zone 8b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 11 – Mar 25	May 13 – May 20	Jul 12 – Aug 1	—	matures comfortably
Pepper	Very tender	Feb 25 – Mar 11	May 20 – May 27	Jul 19 – Aug 18	—	matures comfortably
Cucumber	Tender	Apr 8 – Apr 15	May 13 – May 20	Jul 2 – Jul 22	—	matures comfortably
Summer squash / zucchini	Tender	—	May 13 – May 20	Jun 27 – Jul 12	—	matures comfortably
Bush bean	Tender	—	May 13 – May 20	Jul 2 – Jul 12	Aug 19 – Aug 29	matures comfortably
Sweet corn	Tender	—	May 6 – May 20	Jul 5 – Aug 4	—	matures comfortably
Basil	Very tender	Mar 25 – Apr 8	May 13 – May 20	Jun 12 – Jun 27	—	matures comfortably
Lettuce	Half-hardy	Mar 25 – Apr 8	Apr 8 – Apr 22	May 23 – Jun 7	Aug 5 – Aug 20	matures comfortably
Pea	Hardy	—	Mar 25 – Apr 8	May 19 – Jun 3	Jul 26 – Aug 10	matures comfortably
Spinach	Hardy	—	Mar 25 – Apr 8	May 4 – May 14	Aug 15 – Aug 25	matures comfortably
Carrot	Half-hardy	—	Apr 15 – Apr 22	Jun 14 – Jul 4	Jul 16 – Aug 5	matures comfortably
Broccoli	Half-hardy	Mar 11 – Mar 25	Apr 8 – Apr 22	Jun 2 – Jun 22	Jul 21 – Aug 10	matures comfortably

Which crops fit this growing season

Using Nikolski's own 164-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 (Nikolski)

From NOAA's 1991–2020 Climate Normals at station USC00502587. 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), Nikolski.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 26	Jun 11	Oct 1	Oct 19	126
32°F (freeze)	May 6	May 22	Oct 18	Nov 5	164
28°F	Apr 19	May 5	Nov 4	Dec 1	198
24°F	Mar 31	Apr 17	Nov 22	Jan 4	240

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 2 locations is 145; Nikolski's own reading is shown below.

Annual growing degree days for Nikolski (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	250	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	1,571	cool-season crops (brassicas, greens)

Hardiness zone 8b in Alaska

Zone 8b means an average annual extreme minimum winter temperature of about 15 to 20 °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, 7a, 7b, 8a.

Explore zone 8b in other states at zone 8b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 8b mean in Alaska?: Zone 8b means an average annual extreme minimum winter temperature of 15 to 20 °F — the standard USDA measure of which perennials survive winter. 2 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 8b is the growing season longest?: Nikolski runs the longest season on this page at about 164 days; Adak is shortest at about 128 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 8b?: Using Nikolski's frost dates (this page's median-season location): start seeds indoors about Mar 11 – Mar 25, then transplant outside about May 13 – May 20. 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 8b 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 2 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.