Why Are Gardenias Yellow?

General Care

• Gardenias are finicky plants. They require high humidity and a temperature from 68 to 74 degrees Fahrenheit. Outdoors, plant them in partial shade, and indoors, gardenias need full sun. Misting the foliage is not advised as it can lead to fungal problems for the leaves. The soil must be damp and fertilized between April and November.

Cankers

• Canker is a very common gardenia disease and will show as a swollen stem below or near the soil line. The stem above the canker will be bright yellow. There is no treatment for cankers, as affected plants have been stunted in their growth and will die slowly.

Bacterial Leaf Spots

• If you have small round spots on the young leaves, you may be looking at a bacterial infection. The spots will enlarge, become pale, and then develop a yellow halo. A severe infection will cause defoliation. Diseased leaves must be removed.

Leaf Spot

• Fungi can cause yellow-haloed spots of various sizes and is controlled by foliar fungicide. If left untreated, it can cause premature leaf drop.