When to plant onions
Start onions indoors 8–10 weeks before your last spring frost, then transplant 4 weeks before the frost date.. Enter your ZIP below for exact dates.
The rule
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”
Start indoors 8–10 weeks before setting out. [src]Cited: Johnny's Selected Seeds — Seed-Starting Date Calculator chart
Days to maturity: 100–120 days [src]
Method: Start seeds indoors, then transplant. Frost tolerance: frost-hardy (derived from the planting timing above).
Onions is frost-hardy; it's grown as a spring/summer crop.
Onions planting dates by hardiness zone
| Zone | Start indoors | Transplant / sow | Sow for fall |
|---|---|---|---|
| Zone 10a | October 9 – October 23 | December 11 – December 25 | — |
| Zone 10b | October 14 – October 28 | December 16 – December 30 | — |
| Zone 2a | February 8 – February 22 | April 12 – April 26 | — |
| Zone 2b | February 16 – March 2 | April 20 – May 4 | — |
| Zone 3b | February 11 – February 25 | April 15 – April 29 | — |
| Zone 4a | February 5 – February 19 | April 9 – April 23 | — |
| Zone 4b | February 1 – February 15 | April 5 – April 19 | — |
| Zone 5a | February 3 – February 17 | April 7 – April 21 | — |
| Zone 5b | January 26 – February 9 | March 30 – April 13 | — |
| Zone 6a | January 22 – February 5 | March 26 – April 9 | — |
| Zone 6b | January 15 – January 29 | March 19 – April 2 | — |
| Zone 7a | January 7 – January 21 | March 11 – March 25 | — |
| Zone 7b | December 29 – January 12 | March 2 – March 16 | — |
| Zone 8a | December 18 – January 1 | February 19 – March 5 | — |
| Zone 8b | December 8 – December 22 | February 9 – February 23 | — |
| Zone 9a | November 24 – December 8 | January 26 – February 9 | — |
| Zone 9b | October 27 – November 10 | December 29 – January 12 | — |
What you'll need
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Last verified 2026-07-16. Sources: University of New Hampshire Cooperative Extension — “Growing Vegetables: When to Plant Your Vegetable Garden”; University of Georgia Extension (days to maturity); NOAA NCEI 1991–2020 Climate Normals (frost); USDA 2023 Plant Hardiness Zone Map.