A: Fertilizing trees or any plant is based on soil test results and recommendations from a soil laboratory such as the Rutgers Soil Testing Laboratory, Rutgers Plant Diagnostic Lab, or other soil laboratories that can provide fertilizer recommendations for plant fertilizers. Fertilizer applications should only be applied to soils that are lacking in nutrients. The over application of soil nutrients will not increase the vigor of the tree. For information on how to fertilize a shade tree visit RCE fact sheet FS031, How to Fertilize a Shade Tree. For information on how to properly take a soil test visit RCE fact sheet FS797, Soil Testing for Home Lawns and Gardens.