This project addressed research and extension needs identified by organic high tunnel vegetable growers. Research station and on-farm trials were conducted to manage excess heating (shading, fogging, ventilation); optimize planting schedules for season extension and multicropping; refine organic management of soil health, nutrients, plant pathogens, insect pests and natural enemies; and evaluate net economic returns.

In central Georgia, growing summer lettuce in a high tunnel with 30% shade cloth doubled yields and greatly improved market quality over field-grown lettuce. For lettuce, basil, and arugula planted in September-October, the shade cloth reduced air and soil temperatures in the high tunnel but did not affect yield.

In a three-year trial of fall pac choi followed by baby lettuce or spinach, then spring tomato, a cowpea cover crop grown for 53-55 days prior to pac choi did not significantly improve crop yield or soil health. Weekly fertigation boosted pac choi yields 17% over pre-plant granular organic fertilizer. Yields were also improved by yard waste compost (greens) or cow manure compost (tomato), and both composts enhanced soil organic matter, soil structure, and fertility.

In Florida, high tunnel tomatoes grafted onto disease resistant rootstocks showed markedly greater vigor, higher yields, and increased phosphorus, potassium, calcium, zinc, iron, and copper levels in fruit. Grafting was especially effective in an early (January) planting. However, net returns on the cost of grafting ($3,000/ac) depend on farmgate prices and may be negative for wholesale organic tomato prices ($10-16 per 25 lb box).