S06 - Session O1 - Deep Winter Greenhouses for Organic Production of Vegetables in the Northern United States.

Authors: Mary Rogers *, Leah Worth, Greg Schweser, Claire Flavin Hodge

Deep winter greenhouses (DWGs) are passively heated structures designed for winter production of high-value cold tolerant leafy greens in cold climates. These greenhouses allow growers to extend the season and help meet consumer demand for locally- and organically grown fresh vegetables year-round. Leafy greens, including arugula, lettuce, and mustard crops, are well-adapted to cool growing conditions in deep winter greenhouses, however these production systems are novel, and productivity is highly variable across locations. Researchers and extension educators at the University of Minnesota have partnered with a network of deep winter greenhouse growers to better understand how to increase productivity and crop yield in these unique environments using participatory research methodology. Growers are primarily interested in maximizing yield and quality of leafy greens grown during the typical off-season to expand revenue and meet consumers demands for locally grown, organic produce. To this end, we completed a variety trial consisting of 12-18 different cultivars of commercially available organic cultivars of lettuce (Lactuca sativa) and Asian greens (Brassica rapa). In addition, we sought to optimize production using organic soilless substrates in DWGs and investigated production within distinct periods, or "sub-seasons", characterized by irradiance and photoperiod differences within the long winter season. The experiment was conducted in cooperation with four deep winter greenhouse ( DWG) producers spanning four distinctive regions in Minnesota during the winter of 2018-2019. Planting and harvest dates, overall yield, days to maturity (DTM), and microclimate parameters of temperature, relative humidity, and growing degree days were recorded throughout sub-seasons. This research contributes to increased understanding of cultivar, substrate, and microclimate interactions relevant to organic leafy green production in these unique winter growing environments, and contributes a model for participatory research in collaboration with a grower network formed with support from university extension.