Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Research has shown that there is a potential to grow overwintering bulb onions on Delmarva. In the U.S., a center of overwintering onion production is the eastern part of the Pacific Northwest and northern California. Overwintering onions are winter hardy varieties that initiate bulbs in the shorter days of late winter or early spring and mature in late spring. They are not the same as the short day onions in southern latitudes of the U.S. in Georgia, Texas and the southwest that are planted in October through December and harvested in the mid-spring (Granex or “Vidalia” types). Overwintering onions in our area are direct seeded in late August through the middle of September. Specific overwintering varieties are used. Most overwintering varieties offer 5-7 month storage but still can be mild in taste. Varieties include T-420, Bridger, and HiKeeper. There are shorter keeping sweet onions types that are also overwintered (the WallaWalla types).
Bolting can be a problem and research is underway to identify best planting date/variety combinations to reduce bolting problems.