Rose of Sharon, or shrub althea (Hibiscus syriacus), can reach up to 12 feet in height if not pruned. The bush's large flowers come in hues of blue, red, white or purple, and blossom during the summer and fall months. Because Rose of Sharon blooms on new wood, gardeners should prune their bush every year in late winter, once frost danger has passed. This promotes excessive new growth, resulting in more flowers.
Note any dead, diseased or damaged growth on your Rose of Sharon. Dead growth will not move with the wind and will feel brittle. Damaged or diseased growth bears physical discoloration, wounds or marking.
Cut off this unhealthy wood at its base using pruning tools. Choose anvil pruners for growth 3/4-inch thick or less and lopping shears for thicker growth. In between each cut, spray your tools with disinfectant spray to prevent any bacteria from infecting healthy wood.
Rejuvenate the Rose of Sharon by pruning away up to one-third of the oldest branches. Remove the branches at their base. Choose old and tall growth, which you can identify by its thicker stems.
Thin heavy areas of the bush by trimming branches back to a Y intersection. Thinning prevents Rose of Sharon bushes from becoming too bushy and improves air circulation, which keeps the bush healthy.