Gardenias are evergreen tropical shrubs well loved for their creamy white blooms, rich, spicy fragrance and deep forest green foliage with a glassy finish. Gardenias have specific cultural requirements, and when they are not met, the plant does not perform optimally. When gardenias are compromised by poor cultural conditions, diseases and pests take advantage of the weaknesses.
A frustrating problem with gardenia is bud drop. Buds develop that look healthy, then fall from the plant often before or after being fully developed still looking healthy and fresh. This can occur for a wide range of reasons including root damage, insect feeding, excess rain, drought stress or unusually cold or hot temperatures. Unless the cause can be determined, it is difficult to control, but with proper care of the gardenia, the problem often resolves itself over time.
Sooty mold is an organism that presents as a sticky black substance that, while not deadly to plant tissue directly, can cause tissue death. The black substance prevents sunlight from reaching gardenia leaves, disrupting photosynthesis. This causes leaf tissue to yellow and then die. Even small infections can make the shrub stems and foliage unsightly. Sooty mold is fed by the honeydew left by insects such as aphids, mites and mealy bugs. Controlling these insects help control the appearance of sooty mold; it cannot thrive without the honeydew.
Common Insects and Pests
The fleshy tissues of gardenia shrubs can be a magnet for insects and small garden pests. Aphids and thrips hide under the leaves and around the leaf axils of new tissue. Between feedings, they roam around the plant, sucking out the juices discoloring and desiccating the leaves. Mealybugs, whiteflies and their eggs present as white masses slightly reminiscent of downy mold that collects in the leaf and bud axils. Insecticidal sprays should be used the minute these pests are noticed to prevent a complete infestation.