Rose of Sharon (Hibiscus syriacus) is a long-time garden favorite for valid reasons. The showy flowers have a long blooming period from summer through fall and attract hummingbirds and butterflies. The multi-stemmed shrub is tolerant of poor soil, heat, occasional drought and urban conditions. Hardy in U.S. Department of Agriculture plant hardiness zones 5 through 8, it has few pests or diseases and needs only occasional pruning.
Shape It Up
If you have the space to let rose of Sharon grow to its natural height and shape, not much maintenance pruning is needed. Examine bushes each year to see if they need shaping or trimming. If so, prune rose of Sharon in late winter to early spring while the plant is still dormant and before any new growth emerges. Flower buds form on new growth, so pruning at this time encourages branching and new growth, and doesn't cut off forming flower buds. Remove dead, injured or diseased branches at any time.
Sometimes older shrubs need more severe pruning, especially if they're overgrown. Again, perform the pruning in late winter to early spring. Consider pruning back a seriously overgrown shrub in sequential years to preserve its presence in the landscape. The first winter, cut the plant back by about one-third. Remove dead wood or unthrifty growth. The second winter, cut back another one-third of the growth on the remaining old branches and remove the new growth on the branches you trimmed last winter. Repeat this during the third winter to complete the job.
Increase Flower Size
Left to its own devices, rose of Sharon produces a multitude of medium-sized flowers. To increase the size of the flowers, in early spring prune the bush heavily or cut branches back so they have only two to three leaf buds per branch. Fewer flowers will form, but they should be larger than normal.
Make a Tree
Rose of Sharon makes an attractive small specimen tree. The training process involves pruning during the growing season. During the shrub's first season, choose a single stem to be the trunk or leader and cut all the other stems to the ground. Stake the stem. Leave side branches on the leader but cut them back by half. Prune away any stems that come from the shrub's base. When the leader reaches the desired height, usually around 4 feet tall, prune off the leader's tip in early spring, leaving three leaf buds above the desired height. Let these three branches grow. The following spring, cut them back by half so they'll branch to form the head. When the trunk is strong enough to stand without the stake and the head has formed, remove all the side branches from the trunk.