After a week of rain my gardenia has spots of white on the leaves. Could this be mold?
It would be powdery mildew. You can use neem oil to control this, as long as you do not spray this in full sun, or when it is excessively bright. This article will help: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm