AURORA, Ore. — Oregon State University researchers have shown the state’s strawberry producers how they can increase their yields and produce healthier fruit.
Research conducted at OSU’s North Willamette Research and Extension Center (NWREC) has confirmed that plastic tunnel systems — both low and high tunnels — can significantly extend the growing season and boost the percent of marketable yields for day-neutral strawberries in Oregon.
High and low tunnels help protect strawberry plants from rain and cold, raise temperatures around the plants and extend the growing season.
“We hope we can provide growers with some tools they can use to extend their harvest season to produce fruit outside of the typical season when competition is high and to help meet the market demand for fresh strawberries grown locally in Oregon."
Oregon has long focused on processed June-bearing strawberries, but with growing demand for fresh fruit and increased grower interest, there's an opportunity for Oregon growers to meet local demand, according to Erica Chernoh, an Extension commercial and community horticulturist who leads the OSU Extension Berry Initiative.
Field trials at NWREC and other locations had previously shown that low tunnels extend the strawberry season for day-neutral cultivars. Now, results from a more extensive 2021–2023 trial have confirmed and expanded those findings. The trial evaluated the growth and production of day-neutral strawberries under low tunnels, high tunnels, double tunnels (low tunnel under high tunnel), and open-field conditions.
“We hope we can provide growers with some tools they can use to extend their harvest season to produce fruit outside of the typical season when competition is high and to help meet the market demand for fresh strawberries grown locally in Oregon,” said Chernoh, an assistant professor of practice in the Department of Horticulture in the College of Agricultural Sciences.
There is a great potential for fresh market strawberry production in Oregon, where most of the strawberry harvest is processed rather than sold whole. Growers want to produce fresh, locally grown fruit for the market, which people say they want, Chernoh said.
“There’s an opportunity for Oregon growers to fill that market,” she said. “A lot of fruit is imported from out of state and is harvested at 75% ripeness. We will never compete with the scale of strawberry production in California, but we can produce a great-tasting and fresh Oregon berry that’s available in local markets more than just a few weeks in the summer.”
Tunnel effectiveness
The tunnel research began at NWREC in fall 2021. Researchers tested two popular types of day-neutral strawberries, ‘Albion’ and ‘Seascape,’ planted in both the fall and spring. The plants were grown using organic methods and carefully managed to keep pests [EC1] [EC2] under control. They compared four growing setups: low tunnels, high tunnels, a combination of both (double tunnel), and open fields.
The results showed that strawberries grown under low tunnels had the highest amount of marketable fruit, followed by high tunnels, open field, and double tunnels. Among the two strawberry cultivars, ‘Albion’ produced better results overall — it gave more fruit, larger berries, more plant growth and higher sugar levels.
Temperatures inside each tunnel were tracked every hour, and strawberries were picked twice a week when they were at least three-quarters ripe. One challenge in the study came during the second year when a common soil disease affected the plants and influenced some of the results.
The study focused on season extension techniques adaptable to various farm sizes. While low tunnels required more frequent adjustments, high tunnels offered similar yield benefits with less daily labor.
For strawberry growers, cost is an important factor when deciding whether to use tunnels. Low tunnels are more affordable, with prices ranging from about $42 to $156 per 100-foot row, depending on the materials used. A commonly recommended version, using plastic sheeting, metal hoops, and bungee cords costs around $122 per 100 feet.
High tunnels, on the other hand, are much more expensive. One example — a tunnel that’s 100 feet long and 40 feet wide — costs nearly $6,900 to build. That works out to about $1,718 per 100-foot row, though this can drop to around $1,145 if more rows are added.
While high tunnels are pricier, they may last longer and require less day-to-day maintenance, which could make them a better investment over time.
Chernoh co-authored the OSU Extension publication Low Tunnels for Season Extension in Oregon: Design, Construction and Costs, which provides practical guidance based on research conducted at NWREC.
The research was funded by the Oregon Legislature Berry Initiative and Northwest Center for Small Fruits Research. The OSU Extension Berry Initiative has been supported by the Oregon Legislature since 2017.
