A professional gardener told me that when and how I fertilize my trees is as important as the fertilizer I choose. I was in the habit of fertilizing my trees once a year, either in late winter or early spring.
The gardener recommended that I use a fertilizer with more nitrogen in spring or summer and then fertilize the trees with small amounts of fertilizer several other times during the year. This method is for younger growing trees. For older trees, one good feeding a year will most likely work best for the tree.
You should also be certain not to allow the fertilizer to come in direct contact with roots and leaves from the tree. This can burn and damage the tree. And always read the directions on any fertilizer you purchase. This should tell you how much you need to use and how to apply it.