It looks like your gardenia has a few mealybugs on it.  Mealybugs are insects that feed on the plant sap and if left uncontrolled, can slowly kill the host plant.

We recommend controlling mealybugs with one of these houseplant products:

  1. Earl May Earth Rx Houseplant & Insect Spray
  2. Bonide Houseplant Insecticidal Soap

You would want to apply either of these products weekly until the insects are controlled.