Pruning Rose of Sharon is very easy. But it should be done in late winter, or early spring, when it's bare of leaves.
Like most hibiscus, they do benefit from pruning.
I recommend cutting them back, by removing almost half of the bush.
Older Rose of Sharon bushes can be pruned even harder.
If you don't prune them, the shrubs becomes unsightly and they will also flower less, and produce smaller blooms.
It is very easy to control the size of Hibiscus syriacus by pruning it.
Prune in very early spring, or winter in warm climates such as Florida and California, to avoid removing flower buds.
If you planted it as a privacy hedge, you can keep it trimmed as a hedge. Just prune it like you would a regular hedge. It should be done in spring though.
Rose of Sharon plants are easily trained by pruning to a single trunk creating a treelike top. Or you can trim and train it as an espalier.
I get many e-mails from gardeners complaining that their Rose of Sharon bush isn't flowering anymore.
I am convinced it's because they never pruned it, and I always tell them to prune it next season when it's bare from leaves.
So don't be afraid to plant this Hibiscus syriacus plant in your garden. The pruning is a breeze compared to roses for example.