To prune a rose of Sharon shrub, remove dead and damaged branches down to the main branch. Remove branches growing in the wrong direction, and trim the top to allow greater side growth, starting with the oldest and tallest branches. Remove suckers growing from the bottom of the trunk and the roots. Cut out inner branches that block sunlight, and keep air from reaching the plant's interior. Leave 8 to 12 inches between inner branches to create a cleaner appearance.
Prune rose of Sharon shrubs after leaves fall in late fall or winter, or before buds grow in early spring. Pruning in the summer weakens blooms, making them extra susceptible to low temperatures. It can also delay bloom growth or kill the blooms entirely.
Don't use electric pruning tools. Young shrubs only require hand pruners. Older shrubs might require loppers or a small handsaw. Sterilize tools by soaking them in a mixture of one part bleach and one part water for five minutes to prevent the spread of harmful bacteria.
Reduce the size of trunk branches by two-thirds of the total height in old rose of Sharon shrubs in late autumn or winter to rejuvenate the shrub by encouraging new growth. Lightly trim young shrubs to create more space in the interior, cutting only above leaf buds.