When to Plant Onions in New Hampshire
In New Hampshire, the time to plant onions outside runs from Apr 1 – Apr 15 in Nashua to Apr 25 – May 9 in Berlin. In Manchester, it's Apr 2 – Apr 16. The average last spring frost differs by about 3 weeks across the state (Apr 29 in Nashua, May 23 in Berlin), so use the dates for the town nearest you.
Onions are cold-hardy. Plant sets or transplants early so they grow leaves before long summer days trigger bulbing.
- Start indoors: 10–12 weeks before the last frost.
- Plant outside: 2–4 weeks before the last frost.
Onions planting dates in New Hampshire by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Berlin | 4b | Feb 28 – Mar 14 | Apr 25 – May 9 |
| Claremont | 5b | Feb 19 – Mar 5 | Apr 16 – Apr 30 |
| Concord | 5b | Feb 13 – Feb 27 | Apr 10 – Apr 24 |
| Dover | 6a | Feb 8 – Feb 22 | Apr 5 – Apr 19 |
| Franklin | 5b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Keene | 5b | Feb 19 – Mar 5 | Apr 16 – Apr 30 |
| Laconia | 5b | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Lebanon | 5a | Feb 14 – Feb 28 | Apr 11 – Apr 25 |
| Manchester | 6a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Nashua | 6a | Feb 4 – Feb 18 | Apr 1 – Apr 15 |
| Portsmouth | 6a | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| Rochester | 6a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
| Somersworth | 6a | Feb 5 – Feb 19 | Apr 2 – Apr 16 |
Calculated from each town's average (50%) frost dates, from the nearest NOAA station (1991–2020). Typical dates for the 2027 planting season, based on NOAA's 1991–2020 averages. They are long-term odds, not a forecast: always check your local forecast before planting. Zones: 2023 USDA Plant Hardiness Zone Map (USDA-ARS and Oregon State University). Not the official map; see planthardiness.ars.usda.gov.
See all frost dates in New Hampshire, or the general guide to when to plant onions.
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