High tunnels are a relatively new concept primarily used by vegetable growers for season extension (both spring and fall, but mainly for early spring production). There also are a few Iowa growers raising strawberries and cut flowers. Almost any annual outdoor vegetable crop can be raised successfully in a high tunnel, but the key is profitability. A common structure is 30 × 96 ft and typically costs about $1.60 to $2.35/sq ft (with automatic side rollup). Some crops can be double cropped in a high tunnel (peppers, pole beans, and specialty cucumbers).
Iowa State University
Klavitter, Laura; Walters, Calynn; Haynes, Cynthia L.; Taber, Henry G.; and Howell, Nicholas P., "Forcing Spring Bulbs in High Tunnels for Profitability" (2010). Iowa State Research Farm Progress Reports. 331.