An overdose of nitrogen can result in excessive growth and make plants subject to wind damage. Phosphorus develops roots, flowers and fruit as well as matures seeds. There is only a small amount of the phosphorus in our soils that's in a form plants can absorb. Even when you add phosphorus it becomes bound up and unavailable to plants. To get phosphorus into the rooted area, you must dig down where the roots are to place the nutrient and then water well.
Potassium increases plant resistance to disease and high and low temperatures.
It is available in most soils but rarely needed by trees and shrubs once they are established. Here's some advice on feeding your plants. Use a nitrogen and potassium fertilizer to blast them off into summer. Add iron to get richer green. And watch how you put on your fertilizer.