Winter Produce Potential in Conventional and "Deep Winter" Greenhouses in the Upper Midwest

There is increasing public demand for locally produced food across seasons. In collaboration with the Minnesota greenhouse industry and local restaurateurs and grocers, we identified six vegetable (miniature cucumber—Cucumis sativus var. jawell, red Russian kale—Brassica napus var. pabularia, spinach—Spinacia oleracea var. tyee, and a mesclun mix of arugula—Eruca sativa, mizuna—Brassica rapa var. nipposinica, and red giant mustard—Brassica juncea) and one fruit crop ("day-neutral" strawberry—Fragaria x ananassa cv. Albion) that could be used and/or sold in high volume if locally produced from late fall to early spring. We initiated a study in nine greenhouses across the state of Minnesota to determine the potential of existing facilities for successful off-season production of the aforementioned crops. The environment in each facility was monitored, and potential production issues of each crop were determined at each site.  Sites ranged in location from 44.0717°N to 46.8172° N latitude, resulting in a variety of temperature and daylight conditions. Irradiance, day/night temperature, and humidity were measured every 15 minutes at each location from November 2014 to February 2015 using dataloggers, and carbon dioxide concentration was taken once in January, 2015 in each facility. In addition to geographic location, differences between "conventional" greenhouses (6) and "deep winter" greenhouses (3) were evaluated.  Deep winter greenhouses are passive-solar, greenhouses built for growing produce from late fall to early spring with little energy input. Sites varied markedly in day/night temperature, irradiance, and humidity. For instance, deep winter greenhouses had considerably greater fluctuations in temperature than conventional greenhouses.  Fresh weight of leaves and fruit were collected from the crops identified at each location over different harvest times (November–February). In addition, photosynthetic irradiance and carbon dioxide response curves were collected at each site on each crop on a fully mature leaf.  Variation in the photosynthetic potential of each crop at each facility and differences in yield and nutritional value will be discussed.