The clethra, an ornamental deciduous shrub, is also known as summersweet. Maybe it’s because of its sweet white or pale pink flowers that bloom in late summer and last until early fall. Or because of its delicately sweet shape which is often flocked by bees, hummingbirds and butterflies, the symbols of spring. Clethra, like most shrubs, benefits from an annual trim but should be allowed to retain its shape. Trim clethra’s old growth between mid-February and late April and it will bloom vigorously in summer.
Carefully inspect your clethra shrub for damaged, diseased, broken or winter-killed branches. Prune these branches back to the main stem with one clean cut. Do not leave any stub or it will attract pests and disease.
Remove old wood. The oldest, lowest branches on a clethra shrub should be cut back to ground level. This will encourage clethra to produce new spring growth and more flowers in spring.
Deadhead dead and fading clethra flowers. When spent flowers are left on the shrub, it will direct its energy to producing seed. If you deadhead or remove these flowers, that energy will be redirected to bloom production. To deadhead your clethra shrub's flowers, use your pruning shears to trim the stem back to 1/4 to 1/8 of an inch above the bud below the deadheaded bloom.