With their richly scented white flowers and glossy, evergreen foliage, gardenias are widely used in tropical landscapes. Northern gardeners can grow gardenias indoors as a flowering houseplant, but because this sun-loving shrub requires high levels of humidity, it can be a challenging project. Although somewhat fussy indoors and out, the fragrant rewards of proper gardenia bush care are well worth the effort.
A native of Japan and China, gardenias grow to a dense, mounded height of 2 to 6 feet (depending upon the species) with a similar spread. Leathery foliage is dark green and glossy, 2 to 4 inches wide. Four-inch flowers can be single or double and appear between May and July. Reddish fruits, known as "gardenia hips," may appear in early fall.
Gardenias require moist, acid, well-drained soil that is rich in organic matter. They do not like competition from weeds or ground covers and, according to the Clemson University Extension, "resent root disturbance." A thick layer of root mulch will keep weeds to a minimum and--hopefully--keep the plant happy. Indoors, gardenias need direct sunlight for at least six hours. Outdoors, gardenias can be grown in zones 7 to 10 in full sun to partial shade.
Gardenias require regular pruning, feeding and watering. Gardenia should be pruned after flowering to remove dead, damaged or weak branches and spent flowers. This will encourage stronger growth and increased flower production. Gardenias benefit from regular fertilization with an acid plant food. Plants should be fed in late winter and early summer but never in the fall. Fall feedings can encourage new growth which can be killed by cold temperatures.
Gardenias can fall victim to a variety of diseases including canker, leaf spots, molds and mildews. Canker is the most common disease, causing the trunk of the plant to swell at the soil line. The bark begins to crack and the plant declines. Leaf spots are caused by bacterium or fungi and cause unsightly blemishes on the foliage. Molds and mildews are fungus-based and cause a powdery buildup on leaves.
Whiteflies, aphids and nematodes are common gardenia pests. Whiteflies look like little harmless bits of cotton but they excrete a substance known as honeydew that can encourage the growth of fungus. Aphids are small, sap-sucking insects that congregate on the undersides of leaves and on flower buds. These, too, secrete fungus-attracting honeydew. Nematodes live beneath the soil. These microscopic worms feed on shrub roots and cause root rot and general plant decline.