The gardenia bush is a sweet smelling addition to any garden. However, they suffer from a number of diseases that can damage or kill them. There are a few tricks you can use to prevent these diseases or at least mitigate the damage.
Bud drop is the most common problem suffered by gardenias. Buds will fall off the plant before opening.
This problem can be caused by many factors:
- Too much water
- Too little water
- Temperature fluctuations
- Low humidity
- Very high temperatures
- Transplanting your gardenia
- Some insect infestations
There is not much that can be done to correct temperature problems. The best thing you can do to mitigate is keep the soil around your gardenia moist under all conditions, but never soggy. Transplant your gardenia after flowering is done to minimize bud drop. Use insecticides to destroy any insect infestations.
Stem canker is a fungal growth. It is identified by a swelling in the stem at or just below the soil line. The stem above the growth will become yellow. The surface of the stem will become corky. Cracks will develop in the surface of the stem, extending lengthwise up.
There is no way to treat canker. It will kill your gardenia. The only option is to remove and destroy the plant. Do not compost any part. Additionally, plant any replacement gardenias in a different location and clean all of your trimming shears and knives to prevent transferring the disease to other plants.
Spots in various colors - reds, yellows and browns - develop on the leaves due to fungal or bacterial infections. In time, the leaves can yellow and fall off.
To avoid this, do not use overhead watering. Plant your bushes with space to grow and room for air to circulate through the leaves. Use sterile soil for new plantings to prevent transferring this disease.
If the case is bad, try applying a foliar fungicide once a week for two or three weeks. Destroy all damaged leaves and clean all tools to prevent transferring the disease to other plants.
Powdery mildew shows up as a white, powdery substance over the surface of the leaves. It occurs most commonly during very humid summers. Sometimes it can occur when plants are placed too close together. The water becomes trapped on the leaves when the air does not circulate around the plants.
Prevent powdery mildew by providing plenty of air circulation around your plants and using drip irrigation instead over overhead watering. Use sterile soils.
Remove powdery mildew with applications of fungicides. Destroy all fallen leaves.
Sooty mold is a fungus that grows on the top of leaves infected with white flies. The white flies leave a honeydew substance on the leaves that forms a perfect home for the black fungus. Sooty mold can become a thick layer across the top of the leaves that blocks sunlight and prevents photosynthesis.
Remove the mold with a wash of mild soap and warm water.