When should you trim knockout roses?

Knockout roses should be pruned just as buds break dormancy. The perfect time to prune is when buds have swelled, but not yet shown leaves. This can be anywhere from February to May, depending on your U.S. Department of Agriculture growing zone.

Knockout roses are a shrub rose and grow vigorously. Prune healthy shoots by one-third to one-half. Cut them back to about two feet below the maximum desirable height you wish them to reach during the growing season. Pruning to maintain the plant's shape is advised during the growing season to trim back shoots that grow longer than others.