Gardenias are desirable for their large ornamental flowers, as well as for their pleasant fragrance. These flowering shrubs are tropical in nature and can be grown outdoors in warm climates or indoors in cooler climates. Unfortunately, they are not easy to grow and can suffer from a number of problems, including those that affect the leaves
Gardenias feature showy blooms.
Gardenias are desirable for their large ornamental flowers, as well as for their pleasant fragrance. These flowering shrubs are tropical in nature and can be grown outdoors in warm climates or indoors in cooler climates. Unfortunately, they are not easy to grow and can suffer from a number of problems, including those that affect the leaves.
Symptoms of leaf problems range from unsightly spots on the leaves to holes on the leaves. The leaves may turn brown, curl up or fall prematurely from the plant. Or, they may be covered with a fine white film. All of these symptoms are indicative of different problems. These symptoms can help you identify the problem and treat the plant.
Leaf problems caused by insects are usually easy to identify, because the insects themselves cluster on the leaves. Aphids in particular are known to infest gardenias. Small and green, pink, yellow or black, they usually cluster on the undersides of the leaves and suck the sap. This causes the leaves to turn yellow and eventually drop off. Other sucking insects include whiteflies, which are tiny and white, scale, which tend to cluster on stems (causing leaf growth to be stunted) and thrips, microscopic sucking insects that leave white specks or streaks on the foliage. Spider mites also infest gardenias and may leave white webbing on the leaves.
Root rot can be a serious problem in gardenias. It is caused by fungi that thrive in overly wet, soggy soils. As the roots of the plant rot, the leaves turn brown and shrivel up, dropping from the plant. Nematodes (microscopic round worms) also feed on and destroy the roots of gardenias. Fungi are the cause of a white film that can cover the leaves of gardenias. This is called powdery mildew and it spreads in water. Sooty mold is similar to this, only the film is gray or black.
It is common for leaves to turn yellow and drop from the plant in early spring, according to Clemson University Cooperative Extension website. If it happens at other times, however, it can indicate too much or too little water, cold damage, iron deficiency (usually found in soils with a pH level of 7 or higher) and insufficient sunlight.
Treatment and Prevention
Insects can be controlled with regular applications of insecticide. Fungicide and soil drenches are effective against root rot and nematodes, but only if caught in the early stages. To avoid leaf fungal diseases, do not let water sit on the leaves: Water at the soil level only. To avoid fungi problems, plant gardenias in well-draining soil and leave enough room for air to circulate freely around the plants. Protect outdoor gardenias from cold by mulching around the plant in the fall and make sure your gardenia is located in full sunlight.
I hope this helps. -Birdy