Trees and shrubs (especially shade trees) benefit from an annual or at least biennial fertilizer applications. If your trees have been very slow growing or if the foliage is very sparse they may need fertilization. A good way to determine when your plants need fertilizer is by checking the leaf color. If the leaves are light green or yellow green in color, they probably are in need of fertilization.
Fertilization should be done in early spring just as the leaves are coming out. Don’t wait until mid-summer. Late fertilization may cause your trees and shrubs to continue growing into late fall when they could be damaged by freezing temperature.
The feeder roots of nearly all trees and shrubs are in the top foot or two of soil. They usually start a foot or more out from the main trunk and extend out to beyond the spread of the branches. Keeping this in mind, the roots can be fertilized by using tree spikes, a deep root feeder or by using a probe to get the fertilizer down to where it is needed.