Growing Calendar

MenuClose

HomeAboutSearch

When to plant onions in zone 4b

In zone 4b, where the last spring frost typically comes around May 8, start onions indoors January 16 to February 27 and plant out April 10 to 24.

The zone 4b schedule for onions

Start seeds indoors
January 16 to February 27
Plant out
April 10 to 24
Sow outdoors
March 27 to April 10

From the median frost dates of the NOAA stations assigned to the 1,164 ZIP codes in zone 4b, and the timing recommended by Cooperative Extension guides for onions.

Dates before the last frost assume the soil has thawed and is dry enough to work: a squeezed handful crumbles instead of sticking. After a late or wet spring, wait for that even if the date has passed.

Frost risk in zone 4b

Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 4b, the typical last frost ranges from about May 1 in the earliest tenth of ZIP codes to May 25 in the latest tenth, and the first fall frost from September 22 to October 8. For a typical place in the zone:

  • April 26Risky: a later frost happens in 9 years out of 10
  • May 8Typical: frost after this date in half of years
  • May 22Safe: a later frost only 1 year in 10

Your dates for onions

Set your ZIP code at the top of the page and we will work out when to plant onions where you live, from the frost records of the nearest NOAA weather station. Your ZIP code is remembered on this device only.

Enter your ZIP code

Onions in zone 4b cities

CityTypical last frostStart indoorsPlant out
Rochester, MNApr 30Jan 8 to Feb 19Apr 2 to 16
Duluth, MNMay 6Jan 14 to Feb 25Apr 8 to 22
Lakeville, MNMay 2Jan 10 to Feb 21Apr 4 to 18
St. Cloud, MNMay 7Jan 15 to Feb 26Apr 9 to 23
Eau Claire, WIMay 8Jan 16 to Feb 27Apr 10 to 24
Great Falls, MTMay 19Jan 27 to Mar 10Apr 21 to May 5

How to grow onionsAll zonesOnions in zone 4aOnions in zone 5aAbout zone 4b

Sources