The pruning system best suited for all stone fruits that keeps the fruit-bearing surface close to the ground is called the "open center." Pruning and training the trees to this system produces a vase-shaped tree. All stone fruits are very susceptible to brown rot. Open-center trees allow better air circulation and light penetration within the tree--both important factors in reducing the development of brown rot on fruit.
Pruning at Planting
If you purchase an unbranched tree, or one with no branches 20 to 30 inches above the soil line, cut the tree at 26 to 30 inches above the ground after planting. Failure to do so will result in a tree whose major branches are too high above the ground (Figure 5.2). The scaffold branches will develop within 4 to 6 inches below the cut.
If you purchase a tree with healthy branches located 15 to 30 inches above the soil line, select three or four branches, one at each of the compass points. Choose branches that initially develop from the main axis at a 60- to 90-degree angle. Cut them back by one-half to a healthy outside-facing bud. Remove all branches that are less than 15 inches above the soil line and cut the tree off just above the topmost selected scaffold (see Figure 5.2). During the summer, pinch off any shoots that begin to grow toward the center of the tree.
Cut unbranched trees 24 to 30 inches above the soil line. Cut branched trees back to 30 inches and cut three to four side branches in half, removing all others.
By the end of the first summer, trees should begin to take on the typical open vase shape. Three or four permanent scaffold limbs should be selected at this time and the others removed. The permanent or primary scaffolds chosen should be distributed evenly around the trunk, approximately 6 inches apart vertically. Small side branches along the scaffolds can be left for early fruiting. Do not select primary scaffold limbs that are directly above one another. The limbs selected should have an angle of 60 to 90 degrees from vertical.
Pruning the Winter after Planting
Always prune most stone fruit trees in late winter. The best time to prune is from just before bloom to 2 weeks after petal fall. Do not prune the trees from January through March, and do not prune before budswell. Stone fruit trees are very susceptible to a disease called cytospora canker. If pruned in the winter, the trees cannot protect the pruning wounds from infection by this disease. The exception is sweet cherries, which are best pruned after they have fruited or in early July.
First, remove any broken or diseased branches. Second, cut out any vigorous upright shoots that might have developed on the inside of the main scaffolds. Ultimately, prune the tree so it becomes vase shaped with no branches in the center (Figure 5.3).
Figure 5.3. Two-year-old peach tree before (left) and after pruning.
Pruning the Second Winter
Trees that have grown well for 2 years may be 5 to 7 feet tall, 6 to 8 feet wide, and have trunks 3 to 6 inches in diameter. During the second winter after planting, the trees should begin to develop secondary or subscaffold branches on the primary scaffolds. Select two or three limbs per branch that developed during the second summer. They should be spaced 6 to 8 inches apart, 18 to 24 inches from the main trunk, and on opposite sides of the branch (Figure 5.4). Remove all other limbs. Head the chosen side-limbs back by one-half. Head back the primary scaffold by one-half. Large, vertical-growing limbs on the primary scaffolds should be completely removed, leaving only the less vigorous wood for fruiting.
Figure 5.4. Pruning the second winter after planting.
Pruning the Third and Subsequent Years
After careful pruning and training during the first 2 years, heavy pruning should not be necessary. Light corrective pruning should maintain the open center (Figure 5.5). A well trained tree should have 3 to 5 scaffold branches with wide angles evenly distributed around the tree. Thin out and shorten inside limbs to prevent shading of the center. Remove large, branched water sprouts. These shoots may be 4 to 7 feet long. They are not very fruitful and shade the tree center. Prune every year to keep the tree within its allotted space and to prevent limb breakage. Remove vigorous upright branches and leave the less vigorous ones. Head back limbs to encourage the development of new fruiting wood.
Figure 5.5. Mature peach tree before (left) and after pruning.
Pruning Mature Trees
Limit the height and spread of older mature trees. Their height can be limited to 7 to 9 feet tall by removing large branches from the upper side of scaffolds, leaving only small fruit-producing shoots. Head back primary scaffold branches to an outside-growing side branch. Remove or cut back damaged portions of larger branches. Maintain the open center to prevent shading of the interior portion of the tree. Retain shoots that grow horizontally and 12- to 18-inch fruiting shoots, regardless of their orientation. Thin fruiting shoots to a spacing of about 4 to 6 inches apart on the limbs.