Fall fertilization can also help root systems of lawns, trees, and shrubs. For lawns, early and late fall are suggested times for fertilizing. Right now we are somewhat in between, as the next suggested time would be about Halloween or slightly later. Wait until top growth is about done for the year, but the soil is not frozen. Trees and shrubs, although turning color and dropping their leaves, can benefit from a fall fertilizer application.
Soils are still plenty warm for significant root growth that can be helped by fertilizers.
Don't overfertilize trees and shrubs, however, either by a heavy rate or too frequent of application. If the tree was already fertilized in 1999, skip this fall. If in doubt, avoid overfertilizing. When fertilizing trees, it's best to get the fertilizer into the soil, especially if grass is growing over the tree root zone. Root feeders work well.