Why Are Gardenias Yellow?

You're not alone: gardenias are prone to turning yellow naturally

Noted for their white blossoms and pleasing fragrance, gardenias are a popular garden flower. The snow-white blossoms have a tendency to turn yellow with age. Gardenias can experience different maladies which will turn their leaves 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.

References

• Grumpy Gardener: Yellowing Gardenias
• University of Hawaii: Caring for Gardenias
• Perdue University Horticulture: Gardenias

Resources

• University of Rhode Island Horticulture School: Gardenia Care