What does USDA hardiness zone 6b mean in Alaska?

Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 5 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 6b is the growing season longest?

Chignik Lake runs the longest season on this page at about 160 days; St. Paul is shortest at about 114 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 6b?

Using Seldovia's frost dates (this page's median-season location): start seeds indoors about Mar 15 – Mar 29, then transplant outside about May 17 – May 24. 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 6b 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 5 locations listed (see the table above for each location's own dates).

USDA zone 6b in Alaska

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

USDA plant hardiness zone 6b covers 5 locations across Alaska (average annual extreme minimum −5 to 0 °F): Chignik Lake, AK, Hyder, AK, Seldovia, AK, St. Paul, AK, Yakutat, AK. Average last spring frost across this group ranges May 4 (Hyder) to June 4 (St. Paul), and growing seasons run 114–160 days (St. Paul to Chignik Lake) — 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 Seldovia, this group's median-season location.

USDA zone: 6b−5 to 0 °F
Last frost range: May 4–Jun 4avg, 32°F
First frost range: Sep 23–Oct 18avg, 32°F
Growing season range: 114–160days

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)
Chignik Lake	Perryville, Chignik, Ivanof Bay	Sand Point 1 Ene	May 11	Oct 18	160
Hyder	—	Hyder	May 4	Oct 11	157
Seldovia *	—	Seldovia Ap	May 10	Oct 1	145
St. Paul	—	St Paul Island Ap	Jun 4	Sep 28	114
Yakutat	—	Yakutat State Ap	May 20	Sep 23	124

* Seldovia 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 (Seldovia, representative)

Computed from Seldovia's average frost dates — the median-season location in this Alaskazone 6b 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 Seldovia (Alaska, zone 6b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 15 – Mar 29	May 17 – May 24	Jul 16 – Aug 5	—	matures comfortably
Pepper	Very tender	Mar 1 – Mar 15	May 24 – May 31	Jul 23 – Aug 22	—	matures comfortably
Cucumber	Tender	Apr 12 – Apr 19	May 17 – May 24	Jul 6 – Jul 26	—	matures comfortably
Summer squash / zucchini	Tender	—	May 17 – May 24	Jul 1 – Jul 16	—	matures comfortably
Bush bean	Tender	—	May 17 – May 24	Jul 6 – Jul 16	Aug 2 – Aug 12	matures comfortably
Sweet corn	Tender	—	May 10 – May 24	Jul 9 – Aug 8	—	matures comfortably
Basil	Very tender	Mar 29 – Apr 12	May 17 – May 24	Jun 16 – Jul 1	—	matures comfortably
Lettuce	Half-hardy	Mar 29 – Apr 12	Apr 12 – Apr 26	May 27 – Jun 11	Jul 19 – Aug 3	matures comfortably
Pea	Hardy	—	Mar 29 – Apr 12	May 23 – Jun 7	Jul 9 – Jul 24	matures comfortably
Spinach	Hardy	—	Mar 29 – Apr 12	May 8 – May 18	Jul 29 – Aug 8	matures comfortably
Carrot	Half-hardy	—	Apr 19 – Apr 26	Jun 18 – Jul 8	Jun 29 – Jul 19	matures comfortably
Broccoli	Half-hardy	Mar 15 – Mar 29	Apr 12 – Apr 26	Jun 6 – Jun 26	Jul 4 – Jul 24	matures comfortably

Which crops fit this growing season

Using Seldovia's own 145-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 (Seldovia)

From NOAA's 1991–2020 Climate Normals at station USW00025516. 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), Seldovia.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 31	Jun 13	Sep 18	Oct 1	109
32°F (freeze)	May 10	May 24	Oct 1	Oct 17	145
28°F	Apr 22	May 6	Oct 15	Nov 2	177
24°F	Apr 8	Apr 23	Oct 28	Nov 16	202

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 5 locations is 411; Seldovia's own reading is shown below.

Annual growing degree days for Seldovia (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	411	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	1,773	cool-season crops (brassicas, greens)

Hardiness zone 6b in Alaska

Zone 6b means an average annual extreme minimum winter temperature of about −5 to 0 °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, 7a, 7b, 8a, 8b.

Explore zone 6b in other states at zone 6b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 6b mean in Alaska?: Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 5 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 6b is the growing season longest?: Chignik Lake runs the longest season on this page at about 160 days; St. Paul is shortest at about 114 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 6b?: Using Seldovia's frost dates (this page's median-season location): start seeds indoors about Mar 15 – Mar 29, then transplant outside about May 17 – May 24. 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 6b 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 5 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.