Main-season, field- and high tunnel-based vegetable production has received more attention from researchers than ‘off-season’ production. However, this situation is beginning to change as scientific teams and their industry collaborators and stakeholders recognize the value of year-round production, harvest and marketing of fresh market crops, regardless of location.The year-round sale of freshly harvested crops is possible in mid to upper latitudes of the U.S. although the growth of most crops is limited fall to spring in high tunnels lacking supplemental heating or lighting. Moreover, other processes (such as flowering) that respond strongly to environmental signals may produce undesirable outcomes for producers attempting ‘off-season’ production – perhaps especially of biennial species. In many locations, given unalterable natural factors, obtaining and maintaining market-ready crops October to March is a significant test of crop genetic potential and horticultural management. Unraveling the influence of genetics and management during the relatively untested fall-to-spring period will require testing many hypotheses.

Working at the University of New Hampshire, the team of Martin and Sideman asked whether variety and microclimate within a high tunnel influence the yield and quality of winter sprouting broccoli harvested whenever florets reached a marketable condition.They established plots of eleven cultivars in an unheated high tunnel, covering a subset of the plots with row cover. Outcomes were documented from late September to early April in each of the two study years. Ambient temperatures in Durham, NH over the evaluation period ranged from 27°F to 68°F while temperatures within uncovered and covered plots were considerably higher. Row cover use greatly reduced but did not eliminate plant mortality. Differences in cumulative yield among varieties within years were negligible although the length of harvest period varied widely among varieties. Floral shoots were relatively consistent in color and size.

The report by Martin and Sideman provides researchers and growers with additional, foundational information in their respective efforts to explain and profit from genetic and environmental influences on crop behavior, especially fall to spring.