When to plant onions in zone 5b
In zone 5b, where the last spring frost typically comes around May 1, start onions indoors January 9 to February 20 and plant out April 3 to 17.
The zone 5b schedule for onions
- Start seeds indoors
- January 9 to February 20
- Plant out
- April 3 to 17
- Sow outdoors
- March 20 to April 3
From the median frost dates of the NOAA stations assigned to the 2,546 ZIP codes in zone 5b, 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 5b
Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 5b, the typical last frost ranges from about April 21 in the earliest tenth of ZIP codes to May 18 in the latest tenth, and the first fall frost from September 30 to October 19. For a typical place in the zone:
- April 18Risky: a later frost happens in 9 years out of 10
- May 1Typical: frost after this date in half of years
- May 16Safe: 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.
Onions in zone 5b cities
| City | Typical last frost | Start indoors | Plant out |
|---|---|---|---|
| Milwaukee, WI | Apr 19 | Dec 28 to Feb 8 | Mar 22 to Apr 5 |
| Madison, WI | May 1 | Jan 9 to Feb 20 | Apr 3 to 17 |
| Des Moines, IA | Apr 18 | Dec 27 to Feb 7 | Mar 21 to Apr 4 |
| Aurora, IL | Apr 19 | Dec 28 to Feb 8 | Mar 22 to Apr 5 |
| Fort Collins, CO | May 2 | Jan 10 to Feb 21 | Apr 4 to 18 |
| Naperville, IL | Apr 19 | Dec 28 to Feb 8 | Mar 22 to Apr 5 |
| Rockford, IL | Apr 24 | Jan 2 to Feb 13 | Mar 27 to Apr 10 |
| Elgin, IL | Apr 26 | Jan 4 to Feb 15 | Mar 29 to Apr 12 |
| Greeley, CO | May 2 | Jan 10 to Feb 21 | Apr 4 to 18 |
| Green Bay, WI | Apr 30 | Jan 8 to Feb 19 | Apr 2 to 16 |
| Davenport, IA | Apr 19 | Dec 28 to Feb 8 | Mar 22 to Apr 5 |
| Longmont, CO | May 6 | Jan 14 to Feb 25 | Apr 8 to 22 |
How to grow onionsAll zonesOnions in zone 5aOnions in zone 6aAbout zone 5b
Sources
- How to Grow Onions in Your Garden · Utah State University Extension
- Growing Onions in a Home Garden · University of Maryland Extension
- How to Start Onions and Leeks from Seeds · University of Maryland Extension (Maryland Grows)
- Growing Onions - Sets, Plants or Seeds? · Nebraska Extension in Lancaster County
- How to Grow Onions · University of Vermont Extension
- Onions (food fact sheet) · Montana State University Extension
- Planting the Garden · University of Vermont Extension
- Rhode Island Planting Calendar for Fruits and Vegetables · University of Rhode Island Cooperative Extension
- Soil temperature conditions for vegetable seed germination · Oregon State University Extension Service
- Onion, Leek, Shallot, & Garlic (HGIC) · Clemson Cooperative Extension Home & Garden Information Center
- Allium cepa (Plant Toolbox) · NC State Extension
- SP 103/VH021: Florida Vegetable Gardening Guide · University of Florida IFAS Extension
- Onions and Shallots · University of Florida IFAS Gardening Solutions
- Onions (Easy Gardening) · Texas A&M AgriLife Extension
- Vegetable Planting Calendar for Maricopa County (AZ1005) · University of Arizona Cooperative Extension