DibbleWhen to plant onion in Zone 10
In Zone 10, the last spring frost usually passes around January 31 and the first fall frost arrives around December 15, leaving about 318 frost-free days. The windows below are computed from those frost dates, with the same math the Dibble app uses.
Nearly frost-free. Grow cool crops in winter; summers are too hot for many vegetables.
Planting windows for onion in Zone 10
| Task | Window |
|---|---|
| Start seeds indoors | Nov 22 to Dec 6 |
| Transplant | Jan 17 to Jan 31 |
| Estimated harvest | Apr 27 to May 11 |
The harvest estimate counts 100 days to maturity, then a picking window of about 14 days. These windows use typical frost dates for Zone 10; Dibble pins them to your exact ZIP code.
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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 10 planting calendar · Every crop and zone
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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.