To keep your rose of Sharon looking healthy and blooming with full, large blooms, start a routine of regular pruning. Knowing when and how to trim a rose of Sharon will certainly help you, but you must also consider how you want your plant to look. Trimming away at only the lower branches can give you a tree-like shape, while cutting the plant more evenly across the top will keep the shrub looking fuller but shorter. Multiple plants grouped together can be trimmed only along the front and back to form a hedge-shape.
Look over your plants in early spring before any new growth has begun. It will be time for pruning when you notice the buds of new stems just beginning to swell.
Trim back select branches based on the shape you want to encourage, however be sure to leave at least two to three buds leftover on each stem you cut.
Fertilize your plant by adding a tablespoon of granule fertilizer for each foot tall your plant is. Simply spread it around the base of the plant and add 2-4 inches of mulch over it.
Wait until immediately after flowering to cut out any weak wood or unwanted branches. These branches will be the ones which may have only grown a few leaves, if any, over the season and often haven't flowered.