How Do I Get Rid Of Sooty Mold On My Gardenia?

You can use a mixture of two tablespoons Dawn dishwashing liquid and 1 gallon of water.
  Pour it into a sprayer, (the kind you hook to a water hose works well), and spray the leaves really well.
  Is your gardenia planted in a location where it gets good air circulation? This is important to help keep the mold off.