Many people have asked me about trimming shrubs. There are many shrubs on the market and the best advice I can give you is to make sure you ask this question when you purchase the shrub. Usually there is a good tag on each item and if there isn’t please ask.
There is a saying if they bloom in the spring trim them after they have bloomed and if they bloom in the fall trim them in the spring! Some spring bloomers to trim after they bloom: Chokeberry, Forsythia, Lilac, and Early Blooming Spirea. Some shrubs to trim in late fall or early spring before new growth begins: Barberry, Burning Bush, Dogwoods, Honeysuckle, Ninebarks, Purpleleaf Sandcherry, Smokebush, and Sumac. Hydrangea trimming questions: www.finegardening.com or https:www.reference.com There are many types of Hydrangea which should be pruned at different times depending on whether they flower on old or new wood. Many questions have been asked about Hibiscus also. There are many cultivars of Hibiscus. Some are tropical, some are perennial (Rose Mallow)and some are shrubs or Rose of Sharon (Hibiscus syriacus). Rose of Sharon blooms in late summer and early fall. Now is the time to trim the Rose of Sharon since it just got done blooming. I hope this information helps!