Hello!

Rose-of-Sharon pruning should be done in early spring as soon when it won't be cold enough to frost, but before new growth begins because flowering occurs on new growth.

Old and diseased branches can be pruned out at any time. Younger shrubs may benefit from a light pruning while older specimens may need more extreme branch removal. When pruning Rose-of-Sharon, remove wood to the first or second node (bump on the limb). Annual pruning prevents an untidy appearance.

Remove branches that appear to have gone awry or are growing in the wrong direction. Top, upright growth may be pinched back to encourage the growth of side branches. Oldest and tallest stems can be removed first.

Pruning Rose-of-Sharon should include the removal of older, inner branches that disturb the open and airy appearance. Thin out branches which block sunlight or prevent air circulation through the plant. Remove weak branches further down and only prune back healthy branches to the node which allows the desired appearance. As a rule of thumb, allow 8 to 12 inches between inner branches for the best flowering display.

An important step in Rose-of-Sharon pruning is removal of any suckers sprouting from the bottom of the trunk, growing from the roots or spouting in the nearby growing area.

Here is more information on Rose-of-Sharon: http://planttalk.colostate.edu/topics/trees-shrubs-vines/1749-rose-sharon/

Thanks!