Answer: If just the tips of the leaves turn black, it is the result of temperature changes or a possible fungal infection. Prune off the affected leaves to remove any fungal spores and also open your plant up to better air circulation. If there is a powdery coating on the surface of the leaves, it is called sooty mold and is the result of insect feeding. Inspect your plant for signs of aphids, mealybugs or scales. These pests excrete a sticky substance called honeydew which falls onto the leaves below and turns black. If you control the insect pests, the sooty mold will weather away. Best wishes with your gardenia.
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