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University of Rhode Island GreenShare Factsheets

Gardenia Care

 

Gardenias are popular shrubs and ornamentals in the southern part of the United States where severe cold won't damage the plants. Plants always seem to have more blooms at the time you receive them than any other time in their life due to less than favorable growing conditions in most homes.

Gardenias thrive on 68-74 degrees F temperatures in the day, and 60 degrees F evening temperatures. Plants prefer full sun indoors; if grown outdoors for the spring, summer and early fall, keep plants in partial shade. An east or covered west porch will be satisfactory.

High humidity is essential to gardenia care. Avoid misting the foliage, though, as leaf spot fungal problems will develop. The soil should be kept uniformly moist, but don’t overwater. A loose, well-drained organic soil is recommended.

Fertilize monthly between April and November with an acid fertilizer.

Check regularly for insects and other pests such as aphids, mealybugs, spider mites, thrips and scales. Follow recommended control practices if pest problems occur.

The most irritating problem encountered with gardenias is "bud drop,"when flower buds abort just before blooming. Common causes include low humidity, over-watering, under-watering, insufficient light high temperatures, rapid temperature fluctuations, cold drafts or change in plant locations. In other words, gardenias are temperamental!
Plants that do not set flower buds may be experiencing too much warmth.

Disease Problems:

  • Canker (fungus--Phomopsis gardeniae)
    One of the most common gardenia diseases, canker is identifiable by a main stem swollen near or below the soil line. The bark also becomes corky and contains numerous longitudinal cracks in the cankered area. The stem above the canker is bright yellow in contrast to normal greenish white. If the humidity is high, a yellowish substance may be seen on the surface. Affected plants are stunted and die slowly. Destroy all diseased plants to prevent spread of the disease. Place new plants in a different location. Disease is easily spread on propagating knives.
  • Bacterial Leaf Spot (bacteria--Pseudomonas gardeniae, Xanthomonas campestris cv. Maculifolium-gardeniae)
    Small, round ovoid spots on young, tender leaves are the first sign of bacterial leaf spot. As the spots enlarge, the center is at first pale yellow and later becomes reddish-brown surrounded by a yellow halo. Margins of the lesions are thickened and water-soaked in appearance. Spots may coalesce to form large, irregularly shaped spots. Severe infection may cause defoliation. Avoid overhead watering. The disease is spread by taking cuttings from infected plants. Use sterilized soil and pots.
  • Rhizoctonia Leaf Spot (fungus--Rhizoctonia spp.)
    Leaves infected with this fungal leaf spot disease have tan to brown spots up to 1/4 inch in diameter. Spots are circular and zoned. The disease begins on the older leaves and spreads upward when the plants are watered excessively or when air circulates poorly because of overcrowding. Diseased leaves should be destroyed and sterilized soil should be used. Disease-free plants should be used for propagation. Avoid wetting foliage when watering.
  • Leaf Spot (fungi--Cercospora spp., Phyllosticta spp.)
    These fungi cause spots of various sizes on leaves throughout the year. Spots may be small, dark-brown necrotic areas surrounded by a yellow halo. In severe cases, premature leaf drop may occur. Control is obtained by spraying with a folia fungicide at regular intervals.
  • Sooty Mold (fungus--Capnodium spp.)
    Sooty mold causes black, thin layers of the fungus to form over the upper surface of the leaves. Sooty mold is caused by a fungus that grows on sugary exudates from white flies. Control white fly.
  • Bud Drop:
    Bud drop, the abnormal dropping of buds, occurs during periods of high night temperatures or during periods of low light intensity. Some bud drop is a natural condition. Every effort should be made to keep the soil uniformly moist, but not wet, during flowering.
  • Powdery Mildew (fungus--Erysiphe polygoni)
    Powdery mildew is characterized by white, powdery spots on leaves. Use preventive fungicide.
  • Other Diseases:
    Root Knot Nematode, Cotton Root Rot, Crown Gall and Mushroom Root Rot

 

Adapted from the University of Illinois, 2001

Pesticides are poisonous! Read and follow all safety precautions on labels. Handle carefully and store in original containers out of reach of children, pets or livestock. Dispose of empty containers immediately, in a safe manner and place. Pesticides should never be stored with foods or in areas where people eat.

When trade names are used for identification, no product endorsement is implied, nor is discrimination intended against similar materials. Be sure that the pesticide you intend to use is registered for the state of use.

The user of this information assumes all risk for personal injury or property damage.

For more information, call the URI CE Gardening and Food Safety Hotline at 1-800-448-1011 or (401)874-2929 from outside Rhode Island; Monday-Thursday between 9 am and 2 pm.

 

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