Even in the relatively mild climate of western Washington state, growers can gain benefits from growing fresh-market vegetables under high tunnels.
Nevertheless, only about 50 acres of tomatoes and 20 acres of lettuce in the state are under the structures, according to a news release.
Washington State University researchers Suzette Galinato and Carol Miles blame the low adoption rate on a lack of in-depth knowledge about how the structures will perform in the Pacific Northwest.
They published the results of a study that examined regional production practices for tomatoes and lettuce under high tunnels in the journal HortTechnology.
They found that for lettuce, labor cost per square foot of growing area was six times greater in a high tunnel than in the open field.
For tomatoes, the labor cost was 10 times greater in a high tunnel than in the open field.
In either case, total labor comprised more than 50 percent of the total production costs.
But an economic analysis showed that growing lettuce in the open field was 43 percent more profitable than in a high tunnel, whereas tomatoes grown under a high tunnel were three times more profitable than in the open field.
The researchers also conducted focus groups of three to four growers each. Each group examined lettuce or tomatoes and either open field or high tunnel and was asked to develop an enterprise budget.
Participants were selected based on their experience with lettuce or tomatoes in open fields or high tunnels.
Expected yields of both crops were higher when grown in a high tunnel compared with the open field.
But the higher yields weren't enough to offset higher production costs for lettuce.
The researchers pointed out that yield shouldn't be the main driving force when choosing a high-tunnel system over an open-field system.
Instead, they said growers should look at yield, market price and production costs when examining the profitability of any crop and production system.