I have two Gardenia 'Jasminoidas' in containers at the end of my patio. The buds develop tight brown 'covers' on them, preventing them from opening. (I sometimes carefully pull these outer brown 'petals' off, so that the flower can open) The plants look otherwise healthy, green and upright. I live in Northern California; the plants get morning sun to midday. Gets quite hot here, 70-90 degrees. I use an acid fertilizer about every two weeks or so. Help! Please? Thank you so much.
It is possible that you have thrips. They are hard to see and they cause damage to the buds like that. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
This article will help if you feel it is not thrips: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-flowers-gardenia-buds-falling-off-plant.htm
Even if the buds are not technically falling off, the causes for falling off would also be for buds drying out that was not caused by pests.