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When to plant onions in Zone 5a
In Zone 5a, start indoors around February 3 – February 17 and transplant around April 7 – April 21.
Your onions timeline — Zone 5a
| Start indoors | February 3 – February 17 |
|---|---|
| Transplant | April 7 – April 21 |
| Zone 5a last frost | ~05/12 |
| Zone 5a first frost | ~10/01 |
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 5a'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).