How to Prune Althea
Althea is a shrub that can reach up to 12 feet high. Also known as Rose of Sharon, althea is hardy in USDA map zones 5a to 9a. Prune althea in late winter or early spring. Pruning at that time will encourage new growth which is important since althea blooms on new wood. You can prune althea to restrict height or width or to shape the shrub. Pruning can also help to balance the shrub if part of the shrub becomes damaged or diseased. Though young plants tend to put more into root establishment and new growth, if you prune young plants, it may produce more blooms, particularly at the base.
Use hand pruners to cut branches that are 1/2 inch or smaller in diameter. Make cuts about 1 inch from the larger branch to which it is attached. Use loppers to cut large limbs of mature althea or if you need to cut the shrub down to the ground. An althea cut down to the ground will re-grow.
Look for branches that cross one another, and cut the branch that will best open that area of the shrub. Each year for the first 3 years that Althea has been planted, cut the shrub down by 1/3. You can continue to cut off 1/3 of althea each subsequent spring, or allow it to grow tall. Tall, dense althea can create a natural privacy fence. Shorten older althea, if desired, by cutting out the upward growing branch near an intersection of a projecting branch either at the uppermost part of the shrub or lower if you want to shorten the shrub.
Cut out deadwood. Prune off the lower branches at the base of Althea to create a tree-like growth pattern.
Use the lopper to prune althea that has not been pruned for several years. Cut out the thick, old branches at or near ground level. This method to prune althea can be done once a year or every other year to help prevent the shrub from becoming top heavy.