Answer: Gardenias tend to lose their oldest leaves about this time of year, in preparation for producing healthy new foliage. Since only one plant is reacting this way, it might be that it is suffering from some root stress, or there might be an insect problem. Aphids can cause yellowing leaves, as can spider mites. If you find webbing on the undersides of the leaves or where the leaves meet the stems, you've got a spider mite problem. A miticide will take care of them. Hosing the plants off once a week or so will keep spidermites from camping out in your gardenias and will also rinse dust off the leaves. Sometimes a light pruning will encourage a flush of healthy green growth. Hope this helps!
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