Gardenia Mystery Plant Has On Some Leaves Spots Reddish Brown. Not Growing On Those Parts — Other Parts Are Growing Ok.
Affected leaves have "new growth" but they do not grow into new foliage. Should I cut those leaves off?
Certified GKH Gardening Expert
This sounds like it could be a bacterial infection!
I would recommend, only, cutting off the infected leaves. It will, also, benefit from a fungicide. This article will help:
This usually happens from overwatering, or soils that remain too moist for too long. If you can keep it from getting watered until the top two inches of soil are dry, then it will reduce infection. If this is not possible, then you will need to treat with fungicide often.
These articles will help you to care for Gardenia plants: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-plant.htm