Gardenias can be picky plants but don't panic. Is it a houseplant or outdoor  shrub? The most common problems are  lack of water, dry air, poor drainage or too much water. Indoors increase the humidity by misting and do not let the pot set in water. Outdoors keep roots moist and mulched. Too much fertilizer or lack of acid soil can also cause leaf drop. Perhaps if you sent me a photo I could better diagnose your diva gardenia and we can find a reason for this leaf drip tantrum.  Keep Growing, Marianne Binetti