Pistachio, known botanically as pistacia vera, are flowering and fruiting or nut bearing trees that thrive in dry, warm climates and deep, nutrient-rich soil. As dioecious trees, pistachio trees are male or female and need one another to cross pollinate and fertilize their flowers. Pruning regularly on young and middle age trees and less so on older trees as little new branching will result and nut harvest may be impacted. Conduct any significant pruning in the late fall or winter when the tree is dormant.
Prune aggressively during the first five years of life to create an open center with three to five main branches well spaced or a single main branch emanating from the trunk with a secondary leader branch--think of an lopsided V-shape. Remove weaker, smaller branches and water sprouts as needed.
Encourage vigorous and dense branching by making heading cuts deep on the branches to just above a lateral bud and leaf. Place the cut roughly 1/4 inch above the leaf node.
Conduct a light spring pruning to remove any dying, damaged or disease branches that did not survive the winter. Place cuts back to the point of healthy wood and just 1/4 inch above a bud.