Shade trees in the landscape provide shelter from the sun as well as a refreshing visual break of lush green in the garden or yard. According to Oregon State University, young landscape trees with a trunk diameter of 6 inches or less benefit greatly from regular applications of fertilizer, while older, more established trees near manicured lawns or garden beds may need little or none.
Evaluate the need for fertilizer by observing the growth rate and performance of your shade tree. If annual branch growth on a young tree is less than a foot in a year or leaves are shrunken or sparse, fertilizer may be warranted. If the tree has been plagued by an insect infestation or disease, fertilizer may also help it to recover and grow more rapidly.
Select either a slow-release or fast-release, nitrogen-rich, complete fertilizer product with a guaranteed analysis of 20-5-10 or 10-4-6 or a similar ratio of macro-nutrients.
Time the fertilizer application for early to mid-spring each year if using a quick-release water-soluble formulation. Apply in the late summer or early fall if using a slow-release or organic fertilizer formulation.
Apply the fertilizer according to the product label dosing directions; do not exceed a 1/4 lb of fertilizer for every inch of the tree trunk diameter, when measured roughly 4 feet up from the ground. Scale the amount of fertilizer up as the tree grows in diameter.
Cast the fertilizer evenly, several feet out and around the trunk and extending to one and a half times the spread of the tree canopy.
Water the fertilizer into the surrounding soil, drenching the soil to a depth of at least 12 inches to saturate the root zone.