Gardenias are popularly grown for their glossy foliage and sweet-smelling flowers, according to the University of Florida. Landscapers and gardeners often raise them as either outdoor plants or indoor houseplants. Several problems may arise while you're growing the plants, but don't let such problems keep you from enjoying this shrub.
Gardenias have very finicky soil pH needs. Ideally, gardenias should be grown in a soil pH ranging between 5.0 and 6.5, according to the University of Florida. Anything higher, especially a pH greater than 7.0, can result in serious nutritional deficiencies as it affects how the shrub absorbs nutrients. Soil testing kits, available from all garden stores, can identify your soil pH. Consult your regional cooperative extension office to find what amendments are commonly used in your area to adjust pH. Examples include various types of limes, sulfates and phosphates.
Though people commonly grow gardenias indoors as houseplants, indoor gardenias are quite susceptible to poor humidity levels due to the dry air that's prevalent in homes. Gardenias require a high humidity, according to Purdue University. The university recommends operating a humidifier in the same room as the plants or placing a tray of water below the plant.
Bacterial Leaf Spot
The Pseudomonas gardeniae bacterium and several other bacteria strains cause the leaf spot disease on gardenias. Symptoms include wilting of the leaves and round yellow spots on the foliage. Minimize the risks of your gardenias contracting this disease by only using sterile potting soil and avoiding the application of water to the plant's foliage when you water the shrub. Foliar fungicides formulated with chemicals like fixed copper can help control the bacteria.
Aphids may afflict both indoor and outdoor gardenias. Species vary in appearance, with the bugs ranging in color from black to yellow to green. The University of California suggests inspecting your plants twice a week, focusing on leaf stems and blossoms. If you notice these tiny insects, spray the gardenias with neem oil or an insecticidal soap. Both products are widely available at garden stores and nurseries.