The ideal time to prune fruit trees is after the coldest part of winter is over, but before bloom begins. In this area of Colorado that time is now. It’s safer to prune a little bit later rather than earlier—especially with fruit trees. Pruning wounds heal fastest when the tree is just beginning to grow for the season, and that fast healing helps limit problems from pathogens trying to take hold in the cut areas.
Any tree can be pruned while it's in flower and you'll get those same benefits.
Fruit Tree pruning tips:
Remove weak, diseased, injured or narrow-angle branches (the weaker of any crossing or interfering branches), and one branch of forked limbs. Also remove upright branches and any that grow toward the center of tree. You want to keep your tree from becoming too thick and crowded and to keep its height reasonable. All these objectives promote improved bearing, which is your overall aim. A good rule of thumb for fruit trees is to open them up to allow air flow. A bird should easily be able to fly through a properly pruned fruit tree.
Apple, pear, cherry, and most plum trees do best when pruned and trained to a central leader tree. This type of tree has a pyramidal shape with a single upright leader limb as its highest point. This leader is the newest extension of a long, upright growing trunk from which all lateral branches arise. As with all strong growing branches, the leader should be headed back each year. The uppermost bud on the leader produces a vigorous new leader, and no other shoot should be allowed to grow taller. Lateral limbs should be selected from shoots growing out from the central leader. These should be spaced vertically 4-6” apart, have growth that is more horizontal than vertical and point in different compass directions from the trunk.
Peach, nectarine, and apricot trees do best when pruned and trained to a vase-shape. This type of tree should have no central leader. The shape of the tree is controlled by selecting and maintaining three to five main scaffold limbs arising from the trunk. These limbs should point in different directions and originate no less than 18″ and no more than 36” from the ground. Prune as shown, balancing growth evenly between the scaffold limbs.