Fertilizing - In the pear tree’s second year, and each year thereafter, apply a slow-acting general-purpose fertilizer in spring. Sprinkle a granular fertilizer on the soil under the tree out to the dripline. When feeding pear trees, beware of using too much nitrogen. Excessive nitrogen makes pear trees much more vulnerable to fire blight, their most serious disease. It is best to use ammonium nitrate at about 1/8 pound per tree. Use less if the soil is already very fertile. A spray of liquid seaweed extract on pear foliage two or three times during the growing season improves their disease and drought resistance. This provides boron, which pear trees need. An indicator of a healthy, well-fertilized tree is the length of new growth each year. On a dwarf tree, a season’s growth of 8 to 12 inches indicates that the tree is receiving adequate but not excessive nitrogen. On a standard tree, a season’s growth of 12 to 18 inches is good.