I have several hugh bushes which may be as old as 40 years. The main bush is about 30 feet wide and 20 feet high and each year they bloom differently. One year flowers bloomed on only the sides of the main bush and the middle was bare of flowers. Another year, the flowers were very far apart. Last year was the best one yet with flowers covering the entire main bush close together. This year,however, there are hardly any flower buds on the whole thing but the leaves look healthy and there are lots of leaf buds. Does this season after season of different blooming patterns sound normal or is there something I should be doing to make the blooming more consistant?