DibbleWhen to plant onions 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 onions 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.
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Onion in a Zone 9 season
Zone 9 gives about 275 frost-free days. Onion needs roughly 100 days from transplant. That leaves about 175 days of slack, so there is room for a late start or a second planting.
How to grow onions
Start seeds indoors about 8 weeks before planting out, or use sets. Match the variety to your day length (short-day types near the equator, long-day types far from it) and plant out in the cool part of the year. Cure the bulbs in dry weather once the tops fall over.
Companion plants
Good neighbors for Onion:
Better kept apart:
Onion in other zones
Not in Zone 9? Pick your zone for the same dated windows.
Keep exploring
Onion: the full growing guide · The Zone 9 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.