USDA Zone 4b: What to Plant and When
Zone 4b means an average lowest winter temperature of -25 to -20 degrees Fahrenheit (-32 to -29 Celsius).
Your zone will not tell you when to sow. A hardiness zone is a winter survival number and nothing else. It does not give you a last frost date, a growing season length, or any measure of summer heat. Zone 4b runs through Upper Midwest & Northern Plains and Alaska, which share a winter low and almost nothing else: Upper Midwest & Northern Plains has a frost window of May 15 to September 25, Alaska May 15 to September 10. Their sowing calendars are weeks apart. Use your zone to choose fruit trees and perennials, and use your frost dates to schedule everything you sow.
Your growing region in zone 4b
Zone 4b runs through the regions below. Each one has a month by month sowing calendar built on its own frost dates and summer heat, not on the zone number.
| Region | Zone range | Frost window |
|---|---|---|
| Upper Midwest & Northern Plains | 3a-4b | May 15 to September 25 |
| Mountain West | 4a-6b | May 5 to September 30 |
| Alaska | 3a-5b | May 15 to September 10 |
What zone 4b is good for
Any perennial, shrub or fruit tree rated to zone 4b or lower should survive a normal winter where you are. That is the question a zone answers well. For fruit trees there is a second number that matters just as much: winter chill hours, which decide whether a variety will set fruit at all. The free app checks both.
Find your dates
Match your zip code to a region, then check the frost dates table for your sowing window.
Zones changed in 2023. The USDA updated the Plant Hardiness Zone Map in November 2023, the first revision since 2012. It runs about 2.5 degrees Fahrenheit warmer overall and roughly half the country moved up a half zone, with the biggest shifts through the Central Plains and Midwest. If you learned your zone before then, it is worth checking again.