Zone 4b Planting Calendar: What to Plant Each Month
The coldest night of the winter averages -25°F to -20°F in zone 4b. Where it is, when its frosts come, and what to do in the garden each month, from extension service guidance.
Where zone 4b is
Zone 4b covers 1,284 ZIP codes in 15 states: Minnesota (344), Wisconsin (238), South Dakota (183), Montana (129), New York (107), Vermont (70), Wyoming (43), Michigan (38) and 7 more.
Across its 269 NOAA stations the last spring frost comes around May 9 and the first fall frost around Oct 1; half the stations fall between May 5 and May 19 in spring and Sep 25 and Oct 3 in fall.
Cities and towns in zone 4b
- Great Falls, MT 59401
- Pierre, SD 57501
- Laramie, WY 82070
- Rochester, MN 55901
- Eau Claire, WI 54701
- Jackson, WY 83001
- Helena, MT 59601
- Brookings, SD 57006
- St. Johnsbury, VT 05819
- Berlin, NH 03570
- Superior, WI 54880
- Dickinson, ND 58601
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 4b planting calendar
What to start, sow, plant, divide, prune, mulch and protect in zone 4b, 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 269 NOAA stations in zone 4b: last spring frost May 9, first fall frost Oct 1. 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 indoorsJan to May
- Sow vegetables in the gardenApr to May
- Sow the fall vegetable gardenJun to Aug
- Set out transplantsApr to May
- Plant trees and shrubsMar 28 to May 23 and Sep 17 to Nov 5
- Plant garlicSep 17 to Oct 22
- Plant tulips and other spring bulbsOct 8 to Oct 15
- Divide fall-blooming perennialsApr 18 to May 30
- Divide spring and summer-blooming perennialsAug 20 to Oct 1
- Prune trees and summer-flowering shrubs while dormantFeb 28 to Apr 11
- Prune spring-flowering shrubs after they bloomApr 25 to Jun 20
- Water evergreens and new plantings until the ground freezesSep 3 to Nov 12
- Mulch perennial crowns once the ground freezesNov 12 to Nov 26
- Pull back the winter mulchMar 21 to Apr 4
- Put hardware cloth around young tree trunksOct 1 to Nov 12
- Dig and store canna, dahlia and gladiolusOct 1 to Oct 8
- Cut back perennials after a hard freezeOct 8 to Nov 5
What grows in zone 4b
Perennials, shrubs, trees and fruit that NC State Extension rates as hardy in zone 4b, 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 13
- Purple coneflowerzones 3a to 8b
- Orange coneflower (black-eyed Susan)zones 3a to 9b
- Daylilyzones 3a to 9b
- Hostazones 3a to 9b
- Woodland sagezones 4a to 8b
- Coral bells (American alumroot)zones 4a to 9b
- Butterfly weedzones 3a to 9b
- Blue false indigozones 3a to 9b
- Yarrowzones 3a to 9b
- Garden phloxzones 4a to 8b
- Siberian iriszones 3a to 8b
- Showy stonecrop (sedum)zones 4a to 9b
- Rose mallowzones 4a to 9b
Shrubs 8
- 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
- Catawba rhododendronzones 4a to 8b
- Black chokeberryzones 3a to 8b
Trees 5
- Red maplezones 2a to 9b
- Eastern redbudzones 4a to 9b
- Paper birchzones 2a to 7a
- Colorado blue sprucezones 2a to 7a
- Serviceberryzones 3a to 8a
Fruit 6
- Applezones 4a to 9b
- Pearzones 4a to 8b
- Sweet cherryzones 3a to 8b
- Highbush blueberryzones 3a to 8b
- Red raspberryzones 4a to 8b
- American persimmonzones 4a 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 4b
Each half zone is five degrees. Zone 4a is five degrees colder at -30°F to -25°F. Zone 5a is five degrees warmer at -20°F to -15°F.
Zone 4b 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.