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High Tunnels Extend West Side Growing Season for High-value Crops

Mount Vernon, Wash. – Washington State University researchers are exploring the use of high tunnels to help Washington growers earn a higher return on their crops. High tunnels can increase fruit production, improve crop quality, extend the growing season, and reduce disease.

WSU Mount Vernon field day participants checking out trials in one of the high tunnels. Click to download high-resolution image. Photo: Denny Fleener/Washington State University

“We want to help growers on the west side get more return per acre by using high tunnels,” said Tom Walters, small fruit horticulturist. Walters is a member of the high-tunnel research team at the WSU Northwestern Washington Research and Extension Center in Mt. Vernon.

In its second year, the project, funded in part by a U.S. Department of Agriculture specialty crop planning grant, is analyzing the adaptation and economic feasibility of using high tunnels in the cool marine climate of the Pacific Northwest.

The researchers are measuring the growth of tomatoes, strawberries, lettuce and potatoes inside the tunnels versus outside the tunnels to determine if particular varieties are better suited to tunnel production in western Washington. The tunnel influences environmental and pest factors, which will in turn influence variety productivity and suitability for tunnel production, according to Carol Miles, Extension vegetable specialist and research team member.

According to the American Society for Plasticulture, a high tunnel resembles a plastic-covered greenhouse, but is a non-permanent structure. Also, high tunnels have no automated heating or ventilation and are covered with a single layer of 6-mil thick plastic.

WSU researcher Carol Miles addresses field day participants in front of a high tunnel. Click to download high-resolution image. Photo: Denny Fleenor/Washington State University

The researchers are exploring high tunnels as a method for controlling disease in some organically produced crops.

“There can be few effective organic control options for some diseases on some crops,” Miles said. “Growing a disease-free crop can be easier with high tunnels.”

High tunnels increase daytime temperatures and keep rain off the crops. Crops can be started earlier in the season and quality is improved because some disease problems are reduced. Warmer temperatures and shelter from rain also mean that plant leaves dry faster.

“Although leaf wetness looks like it may play an important role, we do not know for sure what causes the reduction of these diseases in the tunnels,” said Walters.

“In western Washington, so far, we have found late blight on tomatoes and Botrytis blight on strawberries to be reduced in high tunnel settings,” said Debra Inglis, a plant pathologist and member of the research team.

Another issue tackled by the researchers is consistency of quality, which is often a problem with strawberries. Under a high tunnel, the strawberry plants produce the same quality week after week. The season starts about a week earlier and extends a little bit longer than usual.

With lettuce, as well, the high tunnels extend the growing season at both ends. Lettuce could be grown year round in a high tunnel, but the structure needs to be taken down because of wind and snowfall during the winter in western Washington.
Miles and Walters are doing intercropping research by planting lettuce and strawberries in the beds at the same time.

“Tunnels are expensive, so we want to see if we can enhance their productivity by growing lettuce between the strawberry plants,” Walters said.

In the intercropping system, strawberries are the primary crop and growers do not want to reduce their yield. At the same time, when strawberries are first planted they are quite small, so if the space between plants can be used to grow a fast crop, such as lettuce, growers can gain from marketing this secondary crop with essentially no additional expenses.

More information on high tunnels and related research can be found at


NOTE: Holly Luka, CAHNRS Marketing and news intern, wrote this news story.

Media Contacts

Carol Miles, Vegetable Extension Specialist, (360) 848-6150
Debra Inglis, Associate Professor of Plant Pathology, (360) 848-6134
Tom Walters, Small Fruit Horticulturist, (360) 848-6124