Fertilization of Trees and Shrubs
Any complete fertilizer that is high in nitrogen and potassium but low in phosphorous is fine for trees. Do not use fertilizer containing a herbicide. Early spring two weeks before the shoot buds open or at the time of leaf fall in autumn are good times to fertilize. Since fall fertilization is usually a supplement to spring fertilization, apply no more than half the total seasonal application in the fall. Once the tree has become established it may not require a specific fertilization.
If a shrub is growing well and shows no signs of nutrient deficiencies you don't need to apply fertilizer. An easy way to fertilize shrubs is to broadcast dry fertilizer over the surface of the soil and water thoroughly. Shrubs on lawns may need no fertilizer as they benefit from fertilization of turf areas.
Methods of Application
Surface Application With Dry Fertilizer: Spread the necessary quantity of fertilizer over the root zone and water well in order to move nutrients into the soil. The zone of absorbing roots begins well beyond the drip line (the circular area on the ground whose perimeter is defined by the outer-most branches of the tree).
Whole Application of Dry Fertilizer: This consists of drilling holes around the tree and filling them with fertilizer. This method allows for the aeration of the soil and deep placement of granular material. Do not fill the hole to the top when working on a lawn. When this is completed water thoroughly and repeat every one to two weeks.