Why are gardenia leaves turning yellow, covered with spots and dropping off?

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Question Why are gardenia leaves turning yellow, covered with spots and dropping off?

Answer It is natural for some evergreen plants to drop a few leaves in the spring. As new leaves pop out, old leaves drop off. Evergreen plants have leaves that stay green all year long. However, that does not mean that each leaf lives forever. The life of an individual leaf varies from plant to plant.

For example, Southern magnolias are evergreen. Each leaf lives for 3 years. That means that one third of the leaves on a Southern magnolia drop off each spring. A live oak is also evergreen. However, it has leaves that only live from one to two years. This means that a live oak drops nearly all its leaves when the new leaves start popping out in the spring.

Plants like hollies, camellias, gardenias, azaleas, and abelias are all evergreen. The age of their leaves may vary from 1 to 5 years. Azaleas, rhododendrons and abelias usually drop leaves in the fall. Gardenias and hollies drop their leaves in the spring.

Additional stress will often cause plants to drop more leaves than usual. If the environment is too dry, wet, hot or cold, then more leaves will turn yellow and hit the ground. Other stresses like soil compaction, nematodes, diseases and insects can also trigger additional leaf drop.

Leaf drop, as a result of stress, is a plant's way of saving its own life. Every plant has a certain ratio of leaves to roots. All of these stresses affect a plant's roots. If a plant has root damage, then the ratio of leaves to roots gets high. Leaves loose water, and roots take in water. If water is leaving the plant at a greater rate than it is coming in, then we have a deficit situation. Plants have to drop leaves in order to regain the correct leaf to shoot ratio. If a plant cannot regain its proper leaf to shoot ratio fast enough, then it will probably die.

Yellow leaves are already dead. Nutrients have been cut off and they are waiting to drop off the plant. Various post-mortem diseases hop on yellow leaves before they fall off. These diseases are not a threat to the living plant. If the green leaves do not have spots, then don’t worry about it.

Mulch, water, and fertilize properly. Do not over fertilize a stressed plant. It will only make things worse. If your plant is not shooting out new leaves or swelling buds, then you may want to be thinking of a replacement plant. Give it another week or two before cranking up the chipper.

Last winter was very cold. Cold is considered a stress that could cause excessive leaf drop. For more info on leaf drop, visit http://viette.indigofiles.com/FoliageSheddingEvergreens.pdf or http://www.clemson.edu/extension/hgic/pests/plant_problems/hgic2353.html If you don’t have internet access or have any further questions, then call me at 910-893-7533 or email me at gpierce@harnett.org

In the plant world, deficit means death. In the political world, deficit simply means election issue (or new taxes). Evergreen leaves may turn yellow and fall off in the spring. Politicians can turn yellow any time of year, but they don’t fall off until November.

Gary L. Pierce

Horticulture Extension Agent