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.

Fertilize 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 and then being 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, you can fertilize the roots by using tree spikes, a root feeder or by using a probe or crow bar to get the fertilizer down to where it is needed. Fertilizer should be applied down to about 12-15 inches deep and every 2-3 feet apart in the area under the tree canopy.

If you're using a root feeder or tree spikes, use the fertilizer designated for the type of tree you're fertilizing. Use a mixed fertilizer such as 20-20-20 or 16-3-8, if you're using a bulk type fertilizer.

Shade trees are fertilized at the rate of one pound per inch of trunk diameter, measured at 4 1/2  feet above ground level. flowering trees should be limited to ½ pound per inch of trunk diameter. Evergreens should have 1/3 pound per foot of height or tree spread, whichever is greater. Shrubs should receive 1/4 pound per foot of height or spread. When shrubs are planted in beds or bare soil, apply 2 pounds of fertilizer per 100 square feet of bed area. As shrubs reach their desired size, reduce or eliminate fertilizer to limit growth.

This page was last updated April 2003

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