Rose of Sharon (Hibiscus syriacus), also known as rose of Althea, is a perennial shrub valued for its large, colorful flowers, drought tolerance and ease of cultivation in the garden. The plant flowers during late summer and early fall, producing numerous blossoms in shades of blue, purple, red, pink and white, depending on the variety. Rose of Sharon bushes commonly reach 8 to 12 feet in height with a spread of up to 10 feet, though annual pruning helps maintain the plants at any desired size. Native to Asia, rose of Sharon thrives in USDA hardiness zones 5 through 9 and makes an ideal planting for perennial borders throughout much of the United States.
Select a planting location for rose of Sharon that consists of moist, well-drained soil and receives full sunlight to light shade throughout the day. Plant rose of Sharon bushes during mid-spring or early fall to give them time to establish their roots before severe hot or cold weather begins.
Dig a hole the same depth and twice as wide as the plant's root ball. Remove the plant from its container and loosen the root structure. Insert the roots into the hole and fill halfway with soil. Water lightly and wait for the water to drain completely. Finish filling the hole with soil, and then water thoroughly to collapse any air pockets.
Spread a 2-inch layer of organic compost over the soil surrounding rose of Sharon bushes each spring, and then cover the compost with a 2-inch layer of mulch. Do not allow the compost or mulch to come within 3 inches of the plant's crown.
Water rose of Sharon bushes once per week during the first season of growth to help establish the root system. Reduce watering thereafter to once per week, but only on weeks that receive less than one inch of rainfall. When watering, soak the soil to a depth of at least six inches to ensure the roots receive enough moisture.
Feed the plants once per year during early spring using a slow-release fertilizer to gradually release nutrients into the soil throughout the growing season. Apply at the rate instructed by the manufacturer for the best results and water thoroughly immediately after feeding.
Prune rose of Sharon bushes during early spring to shape and reduce the size of the plants. Cut back the plant to two or three buds per branch to encourage larger flowers. Use hedge clippers to remove damaged, diseased or dead branches any time of year to improve the plant's overall health.