Production of Bulbing Onion Overwintered in New Hampshire with Protection by Low Tunnels

High demand for local produce year-round has led growers in the northeastern United States to experiment with fall planting of bulbing onion (Allium cepa) for spring harvest. Over two seasons, we evaluated survival, bolting, and bulbing of several cultivars of fall-planted onion in two sites in New Hampshire. Plants were seeded in August and September, and transplanted in September and October into raised beds covered with black plastic mulch. Low tunnels covered with 1.25-oz/yard(2) rowcover and one layer of 6-mil-thick clear polyethylene were installed over the plants in late fall. Harvest dates ranged from 19 Apr. to 6 June in 2012, and from 22 May to 2 July in 2013. All onion cultivars showed high percentages of survival (65% to 100%). Cultivar, planting date, and the interaction between the two had a significant effect on the percentage of bolting and bulb diameter at harvest. In general, those planted later exhibited lower percentages of bolting and slightly smaller bulbs at harvest. Our work demonstrates that it is possible to harvest large bulbed onions in May and June in the northeastern United States in U.S. Department of Agriculture (USDA) hardiness zones 4B and 5B using low-tunnel season extension technology. This may provide additional marketing opportunities for growers in cold climates.