I have an indoor gardenia tree in Long Island, NY. Gardenia's leaves have same yellow but the flowers are also covered with white flakes and some leaves are sticky. Checked under leaves and found tiny white-like mites. Would you have any suggestion on how to save my plants?
It sounds like your gardenia has a mealy bug infestation. These articles have information on treating these bugs, and also keeping your plant healthy so it can ward off such problems. https://www.gardeningknowhow.com/ornamental/flowers/gardenia/growing-gardenias-indoors.htm