Mature fruit trees should receive fertilizer if their branch growth is sub-par or flowering and fruiting has been halted or diminished. Mature fruit trees are generally considered to be underperforming if they produce less than 8 to 10 inches of new branch growth each year.
Less-than-average branch growth calls for a balanced complete fertilizer. When branch growth is on track but fruiting and flowering are failing or diminishing, use a low-nitrogen or nitrogen-free fertilizer once a year to restore vigorous growth.
Determine the type of fertilizer needed by inspecting the tree for appropriate growth and evaluating last season's flowering and fruiting. Choose a balanced and complete fertilizer to spur branch and foliage growth. Choose a low- to no-nitrogen formulation to spur flowering and fruit development.
Calculate the amount of fertilizer using the age and size of the tree and consulting the fertilizer dosing tables. Do not exceed an application rate of 1/8 pound of fertilizer for every inch of the trunk diameter when measuring a foot up the trunk from the soil surface.
Apply the granular fertilizer of choice to fruit trees either in the fall after the leaves have been shed, or in the very early spring a few weeks before the buds break open or new green growth appears.
Cast the fertilizer granules under the canopy of the tree in a wide doughnut formation starting at least a foot out from the trunk and continuing to a few inches past the outer perimeter of the drip line or tree canopy.