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When to plant onions in Zone 10b
In Zone 10b, start indoors around October 14 – October 28 and transplant around December 16 – December 30.
Your onions timeline — Zone 10b
| Start indoors | October 14 – October 28 |
|---|---|
| Transplant | December 16 – December 30 |
| Zone 10b last frost | ~01/20 |
| Zone 10b first frost | ~01/25 |
Start indoors; set out 4 weeks before the last frost. [src]Cited: University of New Hampshire Cooperative Extension — “Growing Vegetables: When to Plant Your Vegetable Garden”
Dates computed from Zone 10b's median NOAA frost normals and the cited rule. Your town may differ by a week or two — check your exact ZIP.
What you'll need
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Last verified 2026-07-16. Frost: NOAA NCEI 1991–2020. Zone: USDA 2023. Rule: University of New Hampshire Cooperative Extension — “Growing Vegetables: When to Plant Your Vegetable Garden”; UGA Extension (days to maturity).