This past week saw some of our coldest mornings in years and you are probably noticing some plants have suffered.
Even a small gardens have their own micro climates of warm and cool areas. If you pay attention to where plants have suffered and where they have been ok, you may find that the higher points or slopes allow the cool air to fall way without settling. Also the shelter of a tree canopy or the eaves of your house can help protect soft plants under. In spring you may want to transplant some of the less hardy plants to the warmer areas in your garden.
Note also that we have had little rain for weeks now, and frost does not contribute any water to your plants. Check how dry the soil is with your finger and keep up the water, at the roots not the leaves, and in the warmest part of the day not in the evening.
For now, leave the damaged parts on the plant until spring comes as this will help protect the plant from further damage. This Gardenia can usually handle frost but several severe frosts in a row will cause stress.