submitted by Don Janssen, Extension Educator
Do the trees in your yard have pale green or off-color leaves that are smaller than usual, dead twigs at the ends of branches, and a general lack of growth and vigor? These are often symptoms that trees need fertilization.
Like lawns, vegetable crops and flowers, landscape trees depend on sunlight, water and certain nutrients from the soil for good growth. Poor soil fertility can also stress trees and make them more susceptible to insect attack, disease and other environmental problems.
The best time to fertilize trees is in the fall, after the growing season. Root growth continues into early December or even later, if weather permits. Fertilizing in fall makes nutrients available for that fall root growth.
You can also fertilize in the spring as soon as the soil is free of frost. Nutrients applied then benefit early spring root growth, which begins well before leaves appear.
Midsummer fertilization is usually reserved for trees that are recovering from defoliation or some other injury. It’s usually best to avoid fertilizing in late summer -- this can cause flushes of new growth that may be damaged by cold winter temperatures.
For homeowners, spreading fertilizer on the soil surface or applying dry or liquid fertilizer by way of holes in the tree’s root zone is usually recommended. Surface application can be tricky because enough nitrogen to meet the tree’s needs may be too much for the surrounding grass. Select a slow release form of nitrogen such as urea formaldehyde.
Applying the fertilizer into holes throughout the tree’s root zone requires a soil auger and some measuring to distribute holes evenly in concentric circles beginning about 3 feet from the trunk and extending outward past the edge of the crown. The rate for nitrogen is 6 pounds of actual nitrogen per 1,000 square feet. To figure out how much to put in each hole, divide the amount needed by the number of holes. Holes should be 1½ to 2 inches in diameter and 12 to 18 inches deep. After adding the fertilizer, fill the holes with peat or some other organic material.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office