Zone 1b covers 11 ZIP codes in Alaska on the 2023 map. Cities in it include Galena, Tanana and Arctic Village in Alaska.

Zone 1b Planting Calendar and Map (-55°F to -50°F)

Q: What does zone 1b mean?

Zone 1b means the coldest night of the winter averages -55°F to -50°F, measured over 1991 to 2020. It is an average of each winter's lowest temperature, so some winters go colder.

Q: When is the last frost in zone 1b?

Across 2 NOAA stations in zone 1b, the median last spring frost is May 24 and the median first fall frost is Sep 3. Half the stations fall between May 21 and May 26 in spring, so check the date for your own ZIP before you plant.

Q: What can I plant in zone 1b?

None of the plants listed here are rated for zone 1b. The hardiest of them are rated down to zone 2a: arrowwood viburnum, red twig dogwood, red maple, paper birch, Colorado blue spruce and asparagus. Gardens this cold lean on annual vegetables grown in the short summer.

Q: What is the difference between zone 1a and 1b?

Five degrees. Zone 1a averages -60°F to -55°F and 1b averages -55°F to -50°F, so 1a is the colder half. A plant rated for zone 1 suits both.

Q: Will a plant rated for zone 2a survive in zone 1b?

Not reliably. A plant rated down to 2a is rated for winter lows of -50°F to -45°F, and a typical zone 1b winter reaches -55°F to -50°F. Choose plants whose range on the tag includes 1b.

11 ZIP codes

Where zone 1b is

Zone 1b covers 11 ZIP codes in Alaska: Alaska (11).

Across its 2 NOAA stations the last spring frost comes around May 24 and the first fall frost around Sep 3.

Cities and towns in zone 1b

Tap a town for its own frost dates and this month’s jobs; a hill or a valley a few miles off can be half a zone either side.

Twelve months

Zone 1b planting calendar

What to start, sow, plant, divide, prune, mulch and protect in zone 1b, month by month. Every job names the extension service page it rests on; open “Where this comes from” under a job to read their words.

Timed from the median frost dates of the 2 NOAA stations in zone 1b: last spring frost May 24, first fall frost Sep 3. Your own ZIP’s frost dates move every window, so the ZIP tool times them for you.

Pick a month above to see every job in it.

The year at a glance

Start vegetable seeds indoorsFeb to May
Sow vegetables in the gardenApr to May
Sow the fall vegetable gardenJun to Jul
Set out transplantsApr to Jun
Plant trees and shrubsApr 12 to Jun 7 and Aug 20 to Oct 8
Plant tulips and other spring bulbsSep 10 to Sep 17
Divide fall-blooming perennialsMay 3 to Jun 14
Divide spring and summer-blooming perennialsJul 23 to Sep 3
Prune trees and summer-flowering shrubs while dormantMar 15 to Apr 26
Prune spring-flowering shrubs after they bloomMay 10 to Jul 5
Water evergreens and new plantings until the ground freezesAug 6 to Oct 15
Mulch perennial crowns once the ground freezesOct 15 to Oct 29
Pull back the winter mulchApr 5 to Apr 19
Put hardware cloth around young tree trunksSep 3 to Oct 15
Dig and store canna, dahlia and gladiolusSep 3 to Sep 10
Cut back perennials after a hard freezeSep 10 to Oct 8

Either side

The zones next to 1b

Each half zone is five degrees. Zone 1a is five degrees colder at -60°F to -55°F. Zone 2a is five degrees warmer at -50°F to -45°F.

Zone 1a, colder-60°F to -55°F Zone 2a, warmer-50°F to -45°F

Questions

Zone 1b questions

What does zone 1b mean?

Where is zone 1b?

When is the last frost in zone 1b?

What can I plant in zone 1b?

What is the difference between zone 1a and 1b?

Will a plant rated for zone 2a survive in zone 1b?

Your own dates, by ZIP

Find your zone by ZIPYour zone, your frost dates and this month’s jobs for your address.Seed starting calendarWhen to start each vegetable indoors, by ZIP.Frost dates by ZIPYour last spring and first fall frost, with the odds either side.First frost forecastWhen the first fall frost usually arrives, state by state.Soil temperatureWhen the ground is warm enough to sow.When to plant garlicThe fall planting window by ZIP.

Sources. USDA Plant Hardiness Zone Map, ZIP code tables (2023 and 2012), PRISM Climate Group, Oregon State University; USDA Plant Hardiness Zone Map; USDA Unveils Updated Plant Hardiness Zone Map (USDA Agricultural Research Service, November 15, 2023); NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal, by station (v1.0.1); NC State Extension Gardener Plant Toolbox. Zone frost dates are the medians of the NOAA 1991 to 2020 station normals inside the zone.

The calendar’s extension sources:

UNH Cooperative Extension, Growing Vegetables: When to Plant your Vegetable Garden, read Sep 21, 2026.
University of Minnesota Extension, Planting vegetables in midsummer for a fall harvest, read Oct 9, 2026.
University of Illinois Extension, Planting a fall vegetable garden (Good Growing), read Oct 9, 2026.
University of Minnesota Extension, Dividing perennials, read Oct 9, 2026.
Iowa State University Extension and Outreach, How should I prepare my perennial beds for winter?, read Oct 9, 2026.
University of Minnesota Extension, Pruning trees and shrubs, read Oct 9, 2026.
Rutgers NJAES Cooperative Extension, Pruning Flowering Shrubs (FS1221), read Oct 9, 2026.
University of Maryland Extension, Planting a Tree or Shrub, read Oct 9, 2026.
University of Wisconsin-Madison Division of Extension, Preparing Landscape Plants for Winter, read Oct 9, 2026.
University of Wisconsin-Madison Division of Extension, Storing Tender Bulbs for Winter, read Oct 9, 2026.
Iowa State University Extension and Outreach, All About Tulips, read Oct 9, 2026.
UF/IFAS Gardening Solutions, Tulips, read Oct 9, 2026.
UF/IFAS Gardening Solutions, Preparing the Landscape for Cold Weather, read Oct 9, 2026.
UF/IFAS Gardening Solutions, Treating Cold-Damaged Plants, read Oct 9, 2026.