What if there is a small hole in the gardenia leaf?

According to what you said, the symptoms should be caused by aphids. You can spray dimethoate on the leaves. Go to the flower market to buy a small bottle of dimethoate pesticide or pesticide that can prevent aphids, and spray it at the above concentration. Because dimethoate is a systemic pesticide, it can also be properly watered or sprayed in pots, especially on the back of leaves. If you turn the leaves upside down, you will see small aphids.