Yields and economics of high tunnels for production of warm-season vegetable crops

Crop development rates, yields and production economics for muskmelon (Cucumis melo), pepper (Capsicum annuum) and tomato (Lycopersicon lycopersicum) grown in high tunnels [4.3 m wide x 2.5 m high x 29 m long (14 x 8 x 96 ft)] were compared to standard low tunnels over several cropping seasons in a temperate production area. The polyethylene-covered high tunnels protect several rows of crop for the duration of the cropping season. Air temperatures in the high tunnels were controlled by raising the sides of the tunnel. Low tunnels cover only a single row and must be removed soon after the crop is established to prevent overcrowding or overheating. When the low tunnels were in place, rates of accumulation of growing-degree days (GDDs) and early crop growth were comparable in the two tunnel systems. However, once the low tunnels were removed, the accumulation of GDDs in the high tunnels exceeded the standard system. The crops in the high tunnels matured 1 to 2 weeks earlier and produced substantially greater fruit yields before frost than in the low tunnel treatments. The high tunnels provided little frost protection and were of limited utility for extension of the growing season. The high tunnels were much more costly to purchase and construct than the low tunnels but were durable enough to be used for multiple cropping seasons. Based on wholesale commodity prices, it would take 2 to 5 years for the enhanced gross returns obtained with the high tunnels to cover their higher capital costs.