Pistachio nuts are actually considered a fruit in the plant world. Pruning is essential to proper nut production and general health of the tree. Cutting away excess branches allows the inside of the tree to receive the proper amount of sunlight for optimum nut production. Maintaining the pistachio tree from a young age will train it to grow to the height and shape you wish and promotes limb growth that allows for maximum sunlight coverage.
Select three to five healthy branches that you will not prune. Make sure they're evenly placed around the tree and not exclusive to one side and aren't directly across from each other. The lowest branch must be over 3 feet from the ground. These branches are called your scaffolds.
Prune all the branches away that are lower than your lowest scaffold branch on the tree. Prune all of the other branches on the tree that are not scaffold branches so that they are 4 to 6 inches from the trunk of the tree. Cutting away excess branches will allow light to come through the tree and keep them from crowding each other, inhibiting fruit production. Cut the scaffold branches down during late spring to promote side branches from the scaffolds.
Cut branches off the top of the tree that you can't reach from the top of your ladder. Cut other branches from the top so that sunlight will reach the scaffolds throughout the tree. This will promote pistachio growth.