When to plant onion in New Hampshire
New Hampshire spans USDA zones 5a–6a, so the right time to plant onion shifts by weeks across the state. The window to transplant seedlings outdoors runs from about April 1 in Nashua to April 16 in Keene — below are local dates for 15 cities, each computed from its own frost dates.
| City | Zone | Last frost | First frost | Transplant out |
|---|---|---|---|---|
| Manchester | 6a | April 30 | October 11 | April 2 – April 16 |
| Nashua | 6a | April 29 | October 8 | April 1 – April 15 |
| Concord | 5b | May 8 | October 3 | April 10 – April 24 |
| Dover | 6a | May 3 | October 10 | April 5 – April 19 |
| Rochester | 6a | April 30 | October 9 | April 2 – April 16 |
| Keene | 5b | May 14 | October 1 | April 16 – April 30 |
| Portsmouth | 6a | May 4 | October 8 | April 6 – April 20 |
| Derry | 6a | April 30 | October 11 | April 2 – April 16 |
Onion in New Hampshire: FAQ
When can I plant onion in New Hampshire?
Across New Hampshire, the time to transplant onion spans roughly April 1 in Nashua to April 16 in Keene, each following that city's local frost dates.
Does the onion planting date vary across New Hampshire?
Yes. New Hampshire publishes 15 cities with their own frost dates, so the right onion planting window shifts by weeks between the warmest and coldest parts of the state — use your city's page for the exact dates.
How long does onion take to grow in New Hampshire?
Onion takes about 90–110 days to reach harvest once planted — check that this fits inside your city's frost-free season on its place page.
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