Zone 3a covers 23 ZIP codes in 2 states on the 2023 map, most of them in Alaska and Minnesota. Cities in it include Fairbanks in Alaska.

Zone 3a Planting Calendar and Hardy Plants (-40°F to -35°F)

Q: What does zone 3a mean?

Zone 3a means the coldest night of the winter averages -40°F to -35°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 3a?

Across 2 NOAA stations in zone 3a, the median last spring frost is Jun 4 and the median first fall frost is Sep 12. Half the stations fall between Jun 1 and Jun 7 in spring, so check the date for your own ZIP before you plant.

Q: What can I plant in zone 3a?

24 of the plants listed here are rated for zone 3a by NC State Extension, including perennials such as purple coneflower, orange coneflower (black-eyed Susan) and daylily and fruit such as sweet cherry and highbush blueberry. Any plant rated for a range that includes 3a should come through a typical winter.

Q: What is the difference between zone 3a and 3b?

Five degrees. Zone 3a averages -40°F to -35°F and 3b averages -35°F to -30°F, so 3a is the colder half. A plant rated for zone 3 suits both.

Q: Will a plant rated for zone 3b survive in zone 3a?

Not reliably. A plant rated down to 3b is rated for winter lows of -35°F to -30°F, and a typical zone 3a winter reaches -40°F to -35°F. Choose plants whose range on the tag includes 3a.

23 ZIP codes

Where zone 3a is

Zone 3a covers 23 ZIP codes in 2 states: Alaska (18), Minnesota (5).

Across its 2 NOAA stations the last spring frost comes around Jun 4 and the first fall frost around Sep 12.

Cities and towns in zone 3a

Fairbanks, AK 99701

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 3a planting calendar

What to start, sow, plant, divide, prune, mulch and protect in zone 3a, 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 3a: last spring frost Jun 4, first fall frost Sep 12. 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 gardenMay to Jun
Sow the fall vegetable gardenJul
Set out transplantsMay to Jun
Plant trees and shrubsApr 23 to Jun 18 and Aug 29 to Oct 17
Plant garlicAug 29 to Oct 3
Plant tulips and other spring bulbsSep 19 to Sep 26
Divide fall-blooming perennialsMay 14 to Jun 25
Divide spring and summer-blooming perennialsAug 1 to Sep 12
Prune trees and summer-flowering shrubs while dormantMar 26 to May 7
Prune spring-flowering shrubs after they bloomMay 21 to Jul 16
Water evergreens and new plantings until the ground freezesAug 15 to Oct 24
Mulch perennial crowns once the ground freezesOct 24 to Nov 7
Pull back the winter mulchApr 16 to Apr 30
Put hardware cloth around young tree trunksSep 12 to Oct 24
Dig and store canna, dahlia and gladiolusSep 12 to Sep 19
Cut back perennials after a hard freezeSep 19 to Oct 17

24 plants

What grows in zone 3a

Perennials, shrubs, trees and fruit that NC State Extension rates as hardy in zone 3a, each linked to its plant page. A plant rated for a range of zones suits every half zone in it, so “zones 4 to 8” covers 4a through 8b.

Perennials 8

Purple coneflowerzones 3a to 8b
Orange coneflower (black-eyed Susan)zones 3a to 9b
Daylilyzones 3a to 9b
Hostazones 3a to 9b
Butterfly weedzones 3a to 9b
Blue false indigozones 3a to 9b
Yarrowzones 3a to 9b
Siberian iriszones 3a to 8b

Shrubs 7

Smooth hydrangeazones 3a to 9b
Common lilaczones 3a to 7a
Japanese spireazones 3a to 8b
Arrowwood viburnumzones 2a to 8b
Red twig dogwoodzones 2a to 7b
Winterberry hollyzones 3a to 9b
Black chokeberryzones 3a to 8b

Trees 4

Red maplezones 2a to 9b
Paper birchzones 2a to 7a
Colorado blue sprucezones 2a to 7a
Serviceberryzones 3a to 8a

Fruit 2

Sweet cherryzones 3a to 8b
Highbush blueberryzones 3a to 8b

Bulbs 2

Tulipzones 3a to 8b
Lilyzones 3a to 8b

Perennial vegetables 1

Asparaguszones 2a to 9b

Ratings from the NC State Extension Gardener Plant Toolbox, read Oct 9, 2026. The zone covers winter cold only; heat, rain and soil decide the rest.

A summer perennial border of yellow black-eyed Susans, purple liatris spikes and silvery Russian sage, with a rose of Sharon shrub behind and small plant labels in the bed — A labeled perennial border in high summer. The zone on a plant tag is the coldest winter it is rated to come through, so a plant rated for zones 4 to 9 suits every half zone from 4a to 9b. “Perennials border in Summer”, Bindersbee, Public domain

Either side

The zones next to 3a

Each half zone is five degrees. Zone 2b is five degrees colder at -45°F to -40°F. Zone 3b is five degrees warmer at -35°F to -30°F.

Zone 2b, colder-45°F to -40°F Zone 3b, warmer-35°F to -30°F

Questions

Zone 3a questions

What does zone 3a mean?

Where is zone 3a?

When is the last frost in zone 3a?

What can I plant in zone 3a?

What is the difference between zone 3a and 3b?

Will a plant rated for zone 3b survive in zone 3a?

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.