Rose of Sharon, a variety of hibiscus, is a deciduous shrub that produces cup-shaped flowers in red, pink, blue, purple and white. Unlike many flowering shrubs, it blooms in late summer or early fall. It prefers a sunny location and well-drained soil and is a low-maintenance plant. If the leaves of your Rose of Sharon are yellowing, consider certain conditions to correct the problem.
Rose of Sharon is a plant that needs careful watering. It likes moisture, but not too much. According to WeekendGardener, soggy soil causes the leaves of Rose of Sharon to yellow and drop off the plant. If your soil has heavy clay or drainage problems, allow the shrub to dry out between waterings. Adding a bit of soil amendment helps to aerate the soil and keep it draining well.
Though Rose of Sharon is generally a plant with few problems, it can suffer from leaf spot. Leaf spot can be caused by either a fungus or bacteria and start out as spots on the leaves of the plant. It can lead to yellowing of the leaves and pustules on the undersides of the leaves. Treatment includes removing the leaves and destroying them and treating the shrub with a fungicide, such as captan or maneb, according to the University of Missouri.
An infestation of aphids can also cause yellowing of leaves on Rose of Sharon shrubs. These tiny insects suck the juices from the leaves causing foliage to pucker and yellow. They can seriously undermine the health of plants if untreated. Spray the shrub with insecticidal soap every two to three days until the aphid population decreases. If the aphids remain, use a pyrethrum spray directly on the aphids.
According to Colorado State University, whiteflies are another garden pest that can cause yellowing of leaves in plants. These insects suck the juices from plants causing a decline in health and discoloration of leaves. Set out sticky traps to capture the insects or use a 2 percent solution of horticultural oil spray to eliminate eggs and larva.
Chlorosis is a nutritional condition of plants that occurs when there is an insufficient amount of iron in the soil for the plant's use. This deficiency will cause yellowing of leaves in your Rose of Sharon. To correct the problem, apply iron chelate to the soil as directed on package instructions. Iron chelate is available at garden stores and plant nurseries.