Q.gardenia/ yellow leaves
my gardenia is in a tub it has been in the same tub for a few years. It now has yellow leaves nearly all over it. i have given it one watering of Debco water soluble food for acid loving plants.
Sorry no photos don’t yet know how to upload them, but whole leaf is yellow and covering most of bush.
Gardenia can be a finicky plants and yellowing of the leaves is a common issue.
This article will help you pinpoint the issue.