DURHAM, N.H. (AP) — Strawberry season in the Northeast usually lasts only four to six weeks, but New Hampshire researchers have figured out how to stretch the harvest form July to Thanksgiving.

Researchers with the University of New Hampshire harvested strawberries grown in low tunnels for 19 consecutive weeks. They also found that the 3-foot (0.91-meter) tall tunnels significantly increased the percentage of marketable fruit, from an average of about 70 percent to 83 percent.

Now in its second year, the research project by the New Hampshire Agricultural Experiment Station is part of a larger,...