Maintaining adequate levels of mineral nutrients in trees is an essential aspect of orchard management. Soil and foliar applications of these elements should occur only after careful observation of tree growth, bud and leaf quality, yield, and fruit quality and after measurement of concentrations with in the tree (through leaf analysis). With regular observation and annual application, nutrient levels can be optimized and tree performance can be maximize. However, environmental or management conditions often interfere with this process, resulting less than optimal nutrient concentrations. Soil applications and postbloom foliar applications often can correct these deviations, but one of the most critical phases of development in an apple tree is from the time growth begins through bloom, since much development of floral parts occur during this period and the ability of flowers to set fruit is determined. Prebloom nutrient applications can be used to supplement nutritional programs during this critical phase. Specific elements that can be targeted during this time are nitrogen, boron, zinc, and copper. The information included in this factsheet was derived from Orchard Nutrition Management by Warren Stiles and Shaw Reid (Cornell Cooperative Extension Information Bulletin 219).