When to Plant Onions in Maine
In Maine, the time to plant onions outside runs from Mar 28 – Apr 11 in Lewiston to Apr 18 – May 2 in Sanford. In Portland, it's Mar 29 – Apr 12. The average last spring frost differs by about 3 weeks across the state (Apr 25 in Lewiston, May 16 in Sanford), 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 Maine by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Auburn | 5b | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Augusta | 5b | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Bangor | 5a | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| Bath | 6a | Feb 15 – Mar 1 | Apr 12 – Apr 26 |
| Belfast | 5b | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Biddeford | 6a | Feb 14 – Feb 28 | Apr 11 – Apr 25 |
| Brewer | 5a | Feb 9 – Feb 23 | Apr 6 – Apr 20 |
| Caribou | 4a | Feb 12 – Feb 26 | Apr 9 – Apr 23 |
| Ellsworth | 5b | Feb 13 – Feb 27 | Apr 10 – Apr 24 |
| Gardiner | 5b | Feb 6 – Feb 20 | Apr 3 – Apr 17 |
| Lewiston | 5b | Jan 31 – Feb 14 | Mar 28 – Apr 11 |
| Old Town | 5a | Feb 18 – Mar 4 | Apr 15 – Apr 29 |
| Portland | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Presque Isle | 4a | Feb 19 – Mar 5 | Apr 16 – Apr 30 |
| Rockland | 6a | Feb 2 – Feb 16 | Mar 30 – Apr 13 |
| Saco | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Sanford | 5b | Feb 21 – Mar 7 | Apr 18 – May 2 |
| South Portland | 6a | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
| Waterville | 5b | Feb 7 – Feb 21 | Apr 4 – Apr 18 |
| Westbrook | 5b | Feb 1 – Feb 15 | Mar 29 – Apr 12 |
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 Maine, or the general guide to when to plant onions.
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