DibbleWhen to plant onion in Zone 9
In Zone 9, the last spring frost usually passes around March 1 and the first fall frost arrives around December 1, leaving about 275 frost-free days. The windows below are computed from those frost dates, with the same math the Dibble app uses.
Very long season. Plant cool crops in fall and winter; manage summer heat.
Planting windows for onion in Zone 9
| Task | Window |
|---|---|
| Start seeds indoors | Dec 21 to Jan 4 |
| Transplant | Feb 15 to Mar 1 |
| Estimated harvest | May 26 to Jun 9 |
The harvest estimate counts 100 days to maturity, then a picking window of about 14 days. These windows use typical frost dates for Zone 9; Dibble pins them to your exact ZIP code.
Get reminders for these exact dates
Dibble turns your ZIP code into a full planting calendar and reminds you on the right day. Free to start, no account needed.
How to grow onion
Start onion seeds indoors 10 weeks before last frost, or use sets. Transplant 2 weeks before last frost, onions are hardy and size up with cool early growth.
Companion plants
Good neighbors for Onion:
Better kept apart:
Onion in nearby zones
Keep exploring
Onion: the full growing guide · The Zone 9 planting calendar · Every crop and zone
Plant at the right time this season
Dibble builds your calendar in under a minute. Free to start, no account needed.
Dates are estimates based on typical frost dates for the zone. Your yard has its own microclimate, so use them as a starting point and adjust as you learn your space.