Based on experience in West China, physiological responses to pruning of orange trees are quite different from apples. While winter pruning in suitable but not excessive amounts stimulates the vegetative processes of apples, it enhances the reproductive processes of citrus and summer pruning does the opposite. As a supplementary practice to winter pruning, summer pruning of oranges at the right time with specific techniques will invigorate neglected and old trees and modify the alter nate bearing habit of healthy trees. During the on-year, trees respond to moderate summer pruning by producing moderate amounts of summer flushes which increases the shedding of young fruits. Thus, the on-year crop will be reduced and the next year crop increased. This is “physiological thinning/’ as compared to chemical or hand thinning. Excessive summer pruning before the time of “June drop” can result in considerable fruit drop.