Answer: Gardenias are not usually bothered by the black spot disease that attacks roses because their leaves are thick and glossy (unlike rose leaves). I wonder if the black specks are the beginnings of sooty mold. This is caused by the feeding of sucking insects such as aphids. When the pests feed they exude a sticky substance which has a high sugar content. The spots turn moldy and a sooty black color. See if you can't wipe the spots off. I think you'll be able to. Yellowing leaves can be caused by poor nutrition or high soil pH. Feed with an acidified fertilizer and topdress with peat moss. It's normal for broadleaf evergreens such as gardenias to lose their oldest leaves (towards the center of the plant). If only the oldest leaves are turning yellow, there's nothing to worry about. The leaves will be replaced in time. If the new leaves are turning yellow, feed and topdress as suggested above. Best wishes with your gardenia.
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