I can't diagnose the problem with your gardenias with that information. I suggest that you take a sample from the plant along with a photo of the plant in its growing location (if possible) to your County Extension Office to see if they can help diagnose the problem and recommend an appropriate course of action. Their contact info is:
Brevard County Extension
3695 Lake Drive, Cocoa, FL 32926
Phone: (321) 633-1702
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