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How to Prune an Overgrown Rose of Sharon Tree

I need information on when to prune rose of Sharon hedge. The hedge I have is over 20 feet tall with foliage and flowers only at the top of the plants. Specifically could I prune the hedge down to say 4-5 feet or lower without damaging the plants? And when to do this – spring or fall? We moved into this home and inherited this hedge that has not been taken care of for many years.
Connecticut

I have developed a deep appreciation for low maintenance shrubs such as rose of Sharon (Hibiscus syriacus), also known as althea. It is one of the few flowers in bloom during the lag time between midsummer and autumn. For that alone it deserves a gold star. Let me share a little background about the plant.

Rose of Sharon is a large deciduous shrub or small tree that grows to about 8 to 10 feet tall and 4 to 6 feet wide. The papery, single petaled blooms are similar in appearance to a hibiscus and range in color from blue to magenta to white. Most have a dark eye. I am particularly fond of the variety ‘White Chiffon’ for its crisp white blooms, which look very refreshing during the heat of late summer.

Rose of Sharon will thrive in just about any soil type although it is sensitive to moisture levels. You will notice that the flower buds will drop before they open if the shrub experiences big swings between dry and excessively moist soil. Making sure the soil is well drained and adding a layer of mulch around the base of the shrub goes a long way in eliminating this problem.

When planting a young shrub, site your rose of Sharon in an area that receives full sun and it will grow rapidly and produce an abundance of blooms with little care.

Rose of Sharon is an old fashioned favorite so it is common for gardeners to inherit one of these shrubs when they move into a new home and more often than not it will be overgrown. Young plants can be cut back pretty hard to encourage branching, but when reshaping an overgrown plant such as yours I always recommend removing only about a third of the length of the branches. In addition to reducing the height you can cut out dead or diseased wood and remove any out-of-control branches back to the base.

Because rose of Sharon blooms on the current season’s growth it should be pruned in late winter. Next winter remove any new growth from the previous year and an additional third from the existing old growth. Continue this pattern in subsequent years until the hedge reaches about 8 feet tall, which is a more natural height for the shrub and about as short as you should take it.

If you have your heart set on a 4 to 5 foot hedge, I recommend that you remove these bushes and try another deciduous flowering shrub such as ‘Limelight’ hydrangea or ‘English Butterfly Purple Emperor’ butterfly bush.