Information on Gardenias With Yellow Leaves

Cultivation

• Ideally, gardenias are grown in daytime temperatures of 68 to 74 degrees F and night temperatures of 60 degrees F. Gardenias grow in full sunlight to partial shade. The flowers also need humidity and fertilizing two or three times a year, with timing depending on your location. Yellowing leaves could indicate cultivation problems, including water deficiency or too much water. Check the soil to determine whether plants are receiving too much or too little moisture. Water the plant more frequently if the soil is excessively dry. Very wet soil could be poorly drained, and may need to be amended. Cold weather also can turn leaves yellow. Foliage can yellow or become discolored from natural causes; for example, old leaves may yellow with age in fall and winter before new leaves develop.

Chlorosis

• Gardenias do best in soil with a pH between 5.0 and 6.0. If pH levels rise dramatically higher than this, the plant can suffer from chlorosis. Iron chlorosis, or iron deficiency, is the most common form of chlorosis. Lack of iron makes the foliage turn pale green or yellowish and growth can be stunted if the problem is not corrected. Apply iron-rich fertilizer to the soil according to package directions to give the plant the nutrients it needs. Another option is to test the soil's pH and make adjustments if it is too alkaline.

Pests

• Aphids feed on the nutrients found inside gardenia stems and leaves. The resulting damage turns foliage yellow. Whiteflies create similar damage by sucking nutrients and sap out of foliage. Plants that are heavily infested may be stunted, and foliage may wilt and die. Insect-killing soaps are effective against both whiteflies and aphids. Mix a few drops of dishwashing liquid with a gallon of water and spray it directly on gardenias, particularly on the underside of leaves, to control these pests. Scale insects also feed on gardenia plants, usually the leaves and stems. The feeding weakens the plants, turning leaves yellow.

Disease

• In early stages, bacterial leaf spot fungus creates pale yellow spots on foliage. Over time, the spots turn reddish-brown. Leaf spot is a fungus that creates dark brown spots ringed with yellow margins. Leaves may wilt and drop from the plant when fungal infection is severe. Root rot is caused by another fungus that attacks the roots of the plant. The damage to the root keeps gardenias from absorbing nutrients and water, turning leaves yellow. The plant may wither and die. Control disease problems with fungicide treatments. Fungal growth is often favored by wet conditions. Do not mist gardenias, and water flowers in the morning, allowing plants to dry naturally in the sun.