How to Care for a Hibiscus Planted Outside
Growing a hibiscus in the garden is like having a little bit of the tropics in your own backyard. The hibiscus is a shrub or tree that produces large, attractive flowers in shades of red, yellow, purple and pink. There are two types of hibiscus commonly grown by the home gardener: hardy hibiscus and tropical hibiscus. They differ not only in hardiness, but in their requirements as well. If the nursery calls it rose mallow, it's a hardy hibiscus. Hardy hibiscus is hardy to USDA Zones 5a to 10b. Tropical hibiscus is hardy to USDA Zones 9b to 11.
Growing Hardy Hibiscus
Ensure that your hardy hibiscus is planted in full sun. It will need at least five hours of sun a day. This plant is heat-tolerant so shade is not important.
Amend the soil around your hibiscus so that it remains slightly acidic. This can be accomplished by adding a handful or two of peat moss to the soil around your plant, and mixing it in. If you have a pH testing kit, aim for the soil pH to be between 6.5 and 7.
Allow the top one inch of soil to dry before you water the hardy hibiscus. Overwatering is the most common problem for this plant.
Fertilize the hardy hibiscus when you see new growth in the spring. Use a balanced fertilizer, such as 10-10-10.
It is not necessary to prune your hardy hibiscus since it will die back in the winter and emerge with all new growth in the spring. You can encourage the plant to grow bushier by pinching back the tips when the plant is between 8 and 12 inches tall.
Attack the hibiscus sawfly promptly as it can decimate your plant. This insect looks like a small, black fly. Researchers at the Connecticut Agricultural Experiment Station recommend using a specialty insecticide product containing spinosad.
Growing Tropical Hibiscus
Ensure that your tropical hibiscus is planted in full sun. If temperatures in your area get above 90 degrees, provide the plant with afternoon shade.
Grow the hibiscus in a slightly acidic soil that drains well.
Water the tropical hibiscus to maintain a consistently moist soil. Remember that on hot days this plant will require a bit more water.
Fertilize the tropical hibiscus with a liquid, water-soluble 7-2-7 solution, once a month during the growing season. You can spray the leaves as well as drench the soil with this spray.
Inspect the tropical hibiscus for insects often. Aphids, thrips and whiteflies are particularly attracted to this plant. Should you need to use an insecticide to control an infestation, water the plant thoroughly prior to application and follow the instructions on the package.
Prune your plant to remove dead branches. Pruning of the entire bush can be done any time, and should be done to encourage new blooms. Make sure to cut just above a leaf node.