Generally, apple trees need fertilizing each year. Nitrogen is the most important essential nutrient. Two other nutrients, phosphorus and potassium, are needed in relatively large amounts when the tree is young; however, after it reaches maturity, it usually requires only nitrogen.
Broadcast 8 ounces of 10-10-10 over a 2-foot circle about 1 month after planting. Keep the fertilizer 6 inches away from the trunk and broadcast it evenly over the recommended area. Do not put any fertilizer in the hole before planting. In June following the planting, broadcast another 8 ounces of 10-10-10 around the tree. Increase the amount of 10-10-10 applied by 0.25 pound per year to 2.5 pounds per tree for a dwarf tree, 5 pounds per tree for a semidwarf, and 10 pounds per tree for a standard tree. Maintain pH at 6.0 to 6.5. (See The Home Fruit Planting: Getting Started for more information on fertility and fertilizers.)