Did you plant it in the ground or keep it in a container? The problem with your gardenia might be caused by poor air circulation. If so, misting the leaves will make it worse. It would be best to water once a week and water the soil rather than the leaves or flowers. Remove dead and dying leaves and cut off any dead branches. If in a container, put your gardenia in a place with bright light, good air circulation, and give it a good watering once a week. It should improve. Also, keep an eye out for signs of insects. If you find any, your local garden center can give you advice on how to treat them.
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