When to Plant Onions in Delaware
In Delaware, the time to plant onions outside runs from Mar 7 – Mar 21 in Dover to Mar 14 – Mar 28 in Milford. In Wilmington, it's Mar 10 – Mar 24.
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 Delaware by city
| City | Zone | Start indoors | Plant outside |
|---|---|---|---|
| Dover | 7b | Jan 10 – Jan 24 | Mar 7 – Mar 21 |
| Elsmere | 7b | Jan 13 – Jan 27 | Mar 10 – Mar 24 |
| Georgetown | 7b | Jan 10 – Jan 24 | Mar 7 – Mar 21 |
| Middletown | 7b | Jan 13 – Jan 27 | Mar 10 – Mar 24 |
| Milford | 7b | Jan 17 – Jan 31 | Mar 14 – Mar 28 |
| Millsboro | 7b | Jan 10 – Jan 24 | Mar 7 – Mar 21 |
| New Castle | 7b | Jan 13 – Jan 27 | Mar 10 – Mar 24 |
| Newark | 7b | Jan 13 – Jan 27 | Mar 10 – Mar 24 |
| Seaford | 7b | Jan 17 – Jan 31 | Mar 14 – Mar 28 |
| Smyrna | 7b | Jan 10 – Jan 24 | Mar 7 – Mar 21 |
| Wilmington | 7b | Jan 13 – Jan 27 | Mar 10 – Mar 24 |
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 Delaware, or the general guide to when to plant onions.
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