My plant is very healthy otherwise and has many buds on it.
Why do my Gardenia flower buds just turn dark and don't bloom?
Last week I did a search on gardenia care already aware how temperamental gardenias are. I ended up at "University of Rhode Island Green Share Factsheet" Altho you didn't say the buds were dropping after turning brown here are some possible causes. Low humidity, over watering, insufficient light, high temperature, rapid temperature fluctuations, cold drafts or change in plant locations. Since you stated your plant is otherwise healthy and isn't diseased sounds like you have a fighting chance, good luck!
Reply:I think it's called blosum rot and caused from high humidity