Winter Broccoli and Cauliflower under Organic High Tunnels in a Humid, Subtropical Climate

Abstract

There is a lack of information related to adapting high tunnel systems to humid, subtropical climates in the Southeastern United States, resulting in a disadvantage for their use to extend growing seasons and meet the increasing demand for local horticulture products. This research project explored the possibility of growing organic broccoli and cauliflower (Brassica oleracea L.) under high tunnels during two consecutive fall/winter seasons in northeast Georgia (USDA plant hardiness zone 8a), particularly evaluating questions related to crop feasibility, planting dates and cultivar choices. Marketable yields for high tunnel broccoli ranged from ≈11,800 to 15,800 kg·ha−1 and were not consistently affected by either planting date or cultivar type. Broccoli required an additional 8–45 days to reach maturity compared with seed catalog estimates with harvesting occurring during mid-December to mid-January. Marketable yields for high tunnel cauliflower ranged from ≈8600 to 26,000 kg·ha−1 and were affected primarily by the cultivar type. Cauliflower required an additional 19–56 days to mature with harvesting occurring during the entire month of January. The first season was cooler than the second with the lowest growing degree days (GDD) units accumulated during the months of January and February. Differences in air temperature at the crop canopy between the high tunnel system and open field were largely related to high tunnel ventilation protocols that changed as the season progressed. An average heat gain of 7 to 8 °C under the high tunnels at crop canopy height was documented on the coldest days and an average of 1 °C gain on the warmest days compared with the open field. Overall, winter broccoli appeared more adaptable to high tunnels than cauliflower but production of both crops may be possible if planting dates and cultivar types are taken into account for the region.