When to plant Onion in Zone 4b
In Zone 4b, Onion: start seeds indoors around Mar 1–Mar 15; transplant outdoors around Apr 12–Apr 26. Expect to harvest around Jul 21–Aug 4.
| Step | When |
|---|---|
| Start seeds indoors | Mar 1 – Mar 15 |
| Transplant outdoors | Apr 12 – Apr 26 |
| Harvest | Jul 21 – Aug 4 |
Tip: Day-length sensitive — match the variety (long/short day) to your latitude for big bulbs.
Zone 4b averages a last spring frost around May 10 and a first fall frost around Sep 22. These are zone averages — look up your ZIP for your exact area.
See the full Zone 4b calendar in the tool →