Growing Gardenias

I have the following problems with my gardenia. Some leaf edges are turning brown while the rest of the tree looks healthy. And, secondly some buds are not opening although the rest on same tree are doing fine and opening to full blooms. These unopened buds become white as if they are trying to open, but they don't in the end. (See the picture, it shows one flower is fine while the upper one is not open.)

By lahib