Leaves dry up, turn yellow and fall off. Why? The plant is in a pot and in acidic soil.
Gardenia Leaves Turning Yellow and Falling Off
Certified GKH Gardening Expert
I highly recommend the following article on the care of indoor gardenias – verify that you are giving your plant the light, temperature, humidity, and watering that it needs:
This article on “Helping A Gardenia Bush With Yellow Leaves” will also help you: