Azalea tree growth blocked by azalea leaves and oak logs

Was making an azalea tree farm, which worked up until the bonemeal dispenser started trying to grow an azalea bush into a tree. No matter how much bonemeal the dispenser used, the azalea bush simply would not grow. I tested this further, and it seems to be because there were azalea leaves & oak logs in the way, neither of which should block the bush from growing.