However, when temperatures rise, lettuce plants begin flowering or bolting. The main stem grows tall with lots of space between the leaves. Then, the leaves turn bitter and lose their juiciness.

Kent Bradford, left, and Alfred Huo, seen here with a flowering lettuce plant, found that lettuce could be prevented from flowering by increasing the expression of a specific microRNA in the plants.

Romaine lettuce, like other members of the Asteraceae, is a self-pollinator. To harvest seeds, you’ll have to allow the plant to grow into the flowering stage where you can then pick off the ...