Evaluation of Eleven Cultivars of Sprouting Broccoli (Brassica oleracea L.) for Potential as An Overwintering Crop for High Tunnels in New England

Eleven winter sprouting broccoli cultivars (Brassica oleracea L.) were sown and cultivated over three years in Durham, NH, from 2007 to 2010, for evaluation as a marketable spring crop. Varieties tested included 5 purple-sprouting, 5 white-sprouting cultivars, and one green annual broccoli (cv.‘DeCicco’) as a control.  Planted in the fall, this biennial vegetable can overwinter in New England conditions under a single layer of rowcover in unheated high tunnels.  Experiments were conducted in a 9.1m by 18.2m (30’ by 90’) unheated high tunnel of gothic design with 6-mil 4-year plastic, manual roll-up sides, and automatic ventilation fans.  Temperature was recorded using HOBO U12 dataloggers to monitor ambient air temperatures outdoors, within tunnels, and within tunnels under a single layer of rowcover. The experimental design was split plot with 4 replications and experimental units of 7 plants. Plants were seeded in mid-August and were transplanted 4 weeks later on 45 cm wide beds in a staggered double row with 23 cm between rows and 38 cm between plants within a row.  All cultivars were evaluated for combined yield of marketable apical and lateral shoots and for winter damage. Marketable shoots were harvested during the months of March and April, and yields ranged from 0.6 to 1.4 kg/m2. While statistically significant differences were detected between the highest and lowest yielding cultivars each year, the yields of most varieties were similar. As a group, white-sprouting cultivars had higher yields than purple-sprouting cultivars (ANOVA F-test, p<0.01).  Many cultivars experienced winter damage when grown in high tunnels without supplemental rowcover. However, all cultivars grown under rowcover in the high tunnel survived extreme low temperatures of -17°C (2°F) on January 16, 2009, when outdoor temperatures dropped to -28°C (-18°F). In conclusion, several winter sprouting broccoli cultivars have potential as a spring crop in cool climate protected culture.