Brown Leaves on Gardenias

The health of the sweet-smelling gardenia shrub can be affected by a number of pests and environmental factors.

Gardenias are sweet-smelling shrubs and ornamentals widely grown in the mild temperatures of the southern United States. The plants thrive with a minimum temperature of 60 F, high humidity, good drainage and fertilization. Improper conditions may cause browning or leaf fungal spots to appear.

Bacterial Leaf Spot

Bacterial leaf spot can be caused by a few different bacteria. The first sign of this type is small, round spots on young leaves. The spots enlarge and the center is at first yellow but becomes reddish-brown with a yellow band. Spots may coalesce and a severe infection causes defoliation. The leaf spot is spread by taking cuttings from infected plants. Growers should avoid overhead watering and use sterilized pots and soil.

Rhizoctonia Leaf Spot

This type of leaf spot is cause by a Rhizoctonia fungus. Infected leaves have circular tan or brown spots up to a quarter inch in diameter. The disease begins on older leaves and spreads upward with over-watering or overcrowding. Growers should use disease-free plants for propagation, avoid wetting foliage during watering, use sterilized soil and destroy infested leaves.

Leaf Spot

Leaf spot can be caused by Cercospora or Phyllosticta fungi. These fungi are responsible for spots, usually dark brown and yellow and of various sizes, on leaves throughout the year. Premature leaf drop may occur. A folia fungicide applied at regular intervals will control leaf spots.

Considerations

Several environmental factors may contribute to a gardenia's brown leaves. Temperature should ideally be between 68 F and 74 F and temperatures below 60 F can seriously damage plant health. Humidity is an essential factor, but growers should ensure that drainage is ample. Gardenias also require acidic soil and at least six hours of sunlight daily.

References

• University of Rhode Island Landscape Horticulture Program: Gardenia Care