Apple trees need to be pruned throughout their lives. The most important period for pruning and training fruit trees is the first 4 to 5 years after planting. Proper pruning and training of young apple trees should produce strong, well-structured trees that yield a large crop of high-quality fruit.
Best Training System
For home gardeners, the easiest training system for apple trees is the central leader system. The central leader system produces a vertical central leader or main stem with tiers of strong, properly spaced limbs or scaffold branches. These scaffold branches grow about 30 to 45 above horizontal. This system of training results in a "Christmas tree" shape or pyramidal-shaped tree.
When to Prune
The best time to prune apple and other fruit trees is late winter or early spring. In Iowa, this is March and early April.
Start Pruning at Planting
Prune newly planted trees immediately after planting. Whips or branchless apple trees should be cut to a height of 30 inches. Make the cut just above a bud. A central leader and several lateral (side) shoots will develop on the upper 8 to 10 inches of the trunk by summer. The following spring (March or early April), retain the central leader and select 3 to 4 well-distributed lateral shoots with wide crotch angles. These lateral shoots will be developed into scaffold branches. Prune off all remaining shoots. Cut back the lateral shoots by 1/4 and the central leader up to 1/2.
When planting a well-branched tree, select and retain 3 to 4 lateral shoots plus the central leader. Remove all other shoots back to the main stem. Retained shoots should have good (wide) crotch angles and be well distributed both around and vertically on the trunk. The lowest shoot should be approximately 2 feet from the soil surface. Cut back the selected shoots and central leader by half their length. Make the cuts just above the buds. If trees have only 1 or 2 desirable lateral shoots, remove the lateral shoots and treat the trees as whips.
Pruning the Second Year
The following spring, there are usually 2 or 3 new shoots at the ends of each scaffold branch. Retain the best positioned of these shoots and remove the others. Remove 25% of the new growth on the retained shoot. The amount of growth made by the central leader determines where to make the cut on the main stem. The second tier of scaffold branches should be about 24 to 30 inches above the top branch of the lower tier. If the distance from the top branch of the lower tier to the top of the central leader is greater than 30 inches, cut off the central leader 30 inches above the top branch of the lower tier. Shorter central leaders (those less than 30 inches in length) should be cut approximately in half. However, make sure the central leader remains the tallest shoot. Slow growing trees will require an additional year of growth before pruning and forming the second tier of scaffolds.
Pruning in Years Three, Four, and Beyond
After two or three years, select a second tier of scaffold branches. Choose 3 to 4 shoots with wide crotch angles that are uniformly distributed around the trunk. No second tier branch should be directly above a first tier branch. Cut back these second tier branches by 1/4. Head back the central leader.
After two growing seasons, use limb spreaders to force the spreading of the first tier scaffolds to 45 branch angles. Spreaders can be made by cutting a notch in each end of a piece of lathe or similar wood. Manufactured spreaders are available from garden centers and mail-order companies. Place the spreader between the central leader and the scaffold branch. Inspect the trees frequently and replace spreaders if they become dislodged. It may be necessary to replace the spreaders with longer ones as the limbs grow. The spreaders should remain in place for 2 to 3 years. The limbs should be stiff enough to remain in the desired position after this period.
Training and pruning in succeeding years should continue the processes of leader development and scaffold selection and training. After several years of training and pruning, the apple tree should have 3 to 4 tiers of scaffold branches. The lower 2 tiers usually consist of 3 to 4 scaffold branches, while there may be only 2 or 3 scaffold branches in the upper tiers. Always keep the upper branches shorter than the lower branches to prevent shading of the lower limbs. When the tree reaches the desired height, cut back the central leader to a weak, outward-growing lateral branch.