Zone 3b Planting Calendar: What to Plant Each Month
The coldest night of the winter averages -35°F to -30°F in zone 3b. Where it is, when its frosts come, and what to do in the garden each month, from extension service guidance.
Where zone 3b is
Zone 3b covers 230 ZIP codes in 6 states: Minnesota (123), North Dakota (54), Alaska (26), Montana (25), Maine (1), Wisconsin (1).
Across its 41 NOAA stations the last spring frost comes around May 17 and the first fall frost around Sep 23; half the stations fall between May 15 and May 24 in spring and Sep 17 and Sep 26 in fall.
Cities and towns in zone 3b
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.
Zone 3b planting calendar
What to start, sow, plant, divide, prune, mulch and protect in zone 3b, 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 41 NOAA stations in zone 3b: last spring frost May 17, first fall frost Sep 23. 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 5 to May 31 and Sep 9 to Oct 28
- Plant garlicSep 9 to Oct 14
- Plant tulips and other spring bulbsSep 30 to Oct 7
- Divide fall-blooming perennialsApr 26 to Jun 7
- Divide spring and summer-blooming perennialsAug 12 to Sep 23
- Prune trees and summer-flowering shrubs while dormantMar 8 to Apr 19
- Prune spring-flowering shrubs after they bloomMay 3 to Jun 28
- Water evergreens and new plantings until the ground freezesAug 26 to Nov 4
- Mulch perennial crowns once the ground freezesNov 4 to Nov 18
- Pull back the winter mulchMar 29 to Apr 12
- Put hardware cloth around young tree trunksSep 23 to Nov 4
- Dig and store canna, dahlia and gladiolusSep 23 to Sep 30
- Cut back perennials after a hard freezeSep 30 to Oct 28
What grows in zone 3b
Perennials, shrubs, trees and fruit that NC State Extension rates as hardy in zone 3b, 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
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.
The zones next to 3b
Each half zone is five degrees. Zone 3a is five degrees colder at -40°F to -35°F. Zone 4a is five degrees warmer at -30°F to -25°F.
Zone 3b questions
Your own dates, 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.