Although these prefer an acidic environment, it is best to avoid vinegar. This is toxic to plants. I would recommend citric acid, or phosphoric acid for this. In any case, there may be an actual deficiency. Can you include a photo? This will help me to see what is going on. In the meantime, here is an article that will help you on their care: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-plant.htm
Answered on July 24, 2019
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