Look for a tree fertilizer with a slow (also called controlled) release of available nitrogen and a low salt index. In addition, look for the product that best suits your region. Each tree gets about one tablespoon per foot tall. It extends in a band approximately half a radius wide below the drip line.
If the drip line is an average distance of 12 feet from the tree, spread the fertilizer in a 6-foot wide band (half a radius) from about 3 feet inside to 3 feet outside the drip line).