When to plant Onion in Zone 4a
In Zone 4a, Onion: start seeds indoors around Mar 6–Mar 20; transplant outdoors around Apr 17–May 1. Expect to harvest around Jul 26–Aug 9.
| Step | When |
|---|---|
| Start seeds indoors | Mar 6 – Mar 20 |
| Transplant outdoors | Apr 17 – May 1 |
| Harvest | Jul 26 – Aug 9 |
Tip: Day-length sensitive — match the variety (long/short day) to your latitude for big bulbs.
Zone 4a averages a last spring frost around May 15 and a first fall frost around Sep 18. These are zone averages — look up your ZIP for your exact area.
See the full Zone 4a calendar in the tool →