Increasing Winter Salad Greens Yield in High Tunnels

There has been a significant increase in grower interest in supplying food for their local communities.  Opportunities include CSA’s, farmer’s markets, farm stands and restaurants.  One of the major limitations to creating sustainable local food systems in northern temperate climates, such as Utah, is growing sufficient produce during the winter months to meet market demands.  High tunnel season-extension technology is one method for providing local markets with year round produce.  Previous studies have shown that row covers within tunnels can be used enhance plant growth when winter temperatures become limiting.  This project evaluates the use of supplemental soil heating, different types of row covers and increased plant populations as potential methods to increase winter salad greens productivity. Smooth leaf spinach (Spinacia oleracea L.) and lamb’s lettuce (Valerianella locusta L.) were transplanted on 5-6 November and left uncovered, covered with Reemay, or with low tunnels. Soil beds growing lamb’s lettuce were also heated or left unheated. In a second experiment, lamb’s lettuce and spinach were transplanted on 13-14 January 2010 with plants spaced at 5, 10, or 15 cm apart (covered with Reemay or low tunnels). Plant were harvested every ten days and fresh weight and leaf number recorded.  The use of row covers significantly increased the growth of spinach and lamb’s lettuce when compared to the uncovered control. Supplemental soil heating did not increase productivity in lamb’s lettuce.  Decreasing plant spacing from 15 cm to 5 or 10 cm significantly increased yield (up to 48%) in both spinach and lamb’s lettuce.  These results suggest that row covers within high tunnels and decreasing plant spacing, are two useful strategies to increase mid-winter salad greens production in cold northern temperate production areas.