(Released: 05 October 1995)
By B. Rosie Lerner
Extension Consumer Horticulture Specialist
Although most people think of spring as the time to fertilize, fall feeding can give trees and shrubs a boost. Not all landscape plants need fertilizer, but young plants and those that are recovering from stress can benefit.
Timing fall fertilizer application is important because feeding too early can promote late fall growth. Young tissue will not have a chance to harden off properly before winter and is likely to be killed. Fertilizer applied too late in the fall will not be taken up by the plants and will be wasted. Roots continue to grow and take in fertilizer as long as soil temperatures are above 40 degrees Fahrenheit. The trees and shrubs themselves are good indicators of when to fertilize. Make your application immediately following leaf drop.
For most plants, 1 pound to 2 pounds of actual nitrogen per 1,000 square feet should be adequate for a late fall fertilization. Cut the application in half for evergreens since they tend to have more shallow root systems. It is difficult to know just how far-spreading the root system of a given tree or shrub is, but a general rule of thumb is that the roots tend to be most active in a band the width of the radius from the trunk to the dripline, centered at the dripline.
Since nitrogen fertilizer is usually quite soluble, you can spread the fertilizer material evenly on the ground in the root zone area, then water the material into the soil. If the area surrounding the tree or shrub is planted to grass, you’ll want to fertilize the entire lawn area to keep the turf uniform. For more information on fertilizing woody plants, contact your county office of the Purdue University Cooperative Extension Service and ask for a copy of HO-140.