A hedge of hibiscus plants (Hibiscus spp.) provides the same screening benefits for your backyard retreat as other evergreens, while filling the space with large, tropical flowers in colors including red, pink, purple and coral. While the genus includes herbaceous perennials, and deciduous and evergreen shrubs, Chinese hibiscus (Hibiscus rosa-sinensis), which grows in U.S. Department of Agriculture plant hardiness zones 9 through 11, and stays green all year needs a tropical environment. Deciduous rose-of-Sharon (Hibiscus syriacus), which grows in USDA zones 5 through 8, grows in cooler climates. Hibiscus shrubs require some light maintenance to shape the hedge and keep it looking its best.
Add a 4-inch layer of bark chip mulch to the ground around the hedge, keeping it a few inches away from the trunks. Replenish the mulch to maintain the 4-inch layer as it decomposes. The mulch eliminates weed competition for nutrients and water, and insulates the soil.
Water the hedge to provide plants with the equivalent of 1 inch of water each week. Don't water if it has rained 1 inch throughout the week. Keep the soil around the hedge evenly moist, but not wet. Hibiscus does not tolerate drought.
Mix an all-purpose, water-soluble fertilizer, such as 10-10-10, at rate of 1 tablespoon fertilizer to 1 gallon of water, or according to label directions. Use the mix to water the soil around the hibiscus. Fertilize each plant in the hedge once every two weeks throughout the growing season from spring through fall.
Check the hibiscus plants frequently for signs of common pests and diseases. Aphids are particularly common on hibiscus, but they can also attract mealybugs, scale, whiteflies and mites. Spray the leaves thoroughly with ready-to-use insecticidal soap to eliminate these pests. Cut off branches to remove areas affected by diseases, such as botrytis blight, leaf spot and canker.
Prune out one-third of the old stems each year in late winter or early spring. Remove any rubbing or crossing branches. Use bypass pruners or loppers to cut the stems back to the ground. Repeat this process annually, removing another one-third of the old branches in the second and third years. After the third year, you'll have removed all the old wood and can begin the cycle again in the fourth year.
Prune back the hedge throughout the growing season to control the size and maintain a uniform shape. Make the pruning cuts just above an outward-growing bud to prevent the growth of inward branches that make the center of the hedge too crowded. Hibiscus are better suited for an informal hedge, so don't use hedge shears to create a perfect box shape like you might see with formal evergreen hedges.
Cover a tropical hibiscus hedge with frost cloth, burlap or blankets if a frost is predicted. This is not necessary with cold-hardy hibiscus. Drive stakes into the ground that are a few inches taller than the hedge so the fabric doesn't touch the plants. Drape the fabric over the stakes with about 6 inches of overlap when multiple pieces of fabric are needed. Use rocks to hold the edges of the fabric on the ground.