The goal of pruning apple trees is three-fold: increase sunlight penetration, remove unproductive wood, and shape the crown into a stable form. This helps increase fruit size, promotes uniform ripening, increases sugar content, and reduces disease and pest problems by allowing better spray coverage and quickening the drying process after rainfall.
Not too long ago I read that a good apple tree should not be a good shade tree. Frequently gardeners let standard-size fruit trees outgrow our ability to effectively use ladders and pruning tools to shape them. Using dwarf or semi-dwarf trees can help solve this problem.
Apple tree buds begin developing the growing season previous to the one in which they mature into fruit. Buds appear on 2- or 3-year-old twigs that are thicker than a pencil. Typically, more buds are formed than can develop into fruit. Growing conditions during bud initiation and the following winter greatly affect the number of buds that flower. Certain cultivars are termed "alternate bearers," meaning they rarely initiate many buds during a year with heavy crop yields.
To minimize cold injury, prune apple trees when they are dormant. February or March is usually a good time. Neglected trees should be pruned back gradually over several years to limit stress on the tree. Topping or shearing off an apple tree is probably the worst thing that can be done. Avoid pruning too close, since flesh wounds heal slowly; leaving part of the branch collar is recommended. Remove suckers or watersprouts, which are fast-growing shoots that rob the tree of nutrients needed for fruit production. These often appear at the base of grafted trees, in crotches and near previous pruning locations.
Any dead, broken or rubbing branches also should be removed. Since downward-growing branches produce few fruit buds and can eventually shade other more productive branches, they should be eliminated too. The lowest branch should be at least three feet from the ground. Prune out some of the interior branches that are shaded and develop lower-quality fruit. This will also open the tree up for easier harvest.
Whorls occur when several branches originate at the same place on the trunk or limb. Joints are weaker here, so determine the best branches and remove the others. Prune out branches that are taller than the central leader of the tree. They can cause the tree to become unbalanced and structurally unsound.
Smith is a University of Illinois Extension Master Gardener in McLean County. For horticulture questions or information about the Master Gardener program, call 309-663-8306 or visit www.mcleanextension.org.