Almost all apple trees are grafted. The mature height of the tree depends on the type of rootstock to which it is grafted. Standard trees, which can exceed 20 feet tall, are grown on normal apple seedling rootstocks. Dwarf and semidwarf trees are grafted onto dwarfing rootstocks, which slow the growth of the trunk and branches. Genetic dwarf trees are naturally dwarf no matter which kind of rootstock they grow on.
Apples bear on long-lived spurs. The fruit forms at the tip of last year’s spur growth, and the spur itself then grows a bit more, off to the side of the fruit. Each spur bears for 10 years or more, so don’t tear it off when you pick.
Although all apple trees bear fruit on spurs, some trees are called spur-types. These are mutations of standard apple trees that produce more fruiting spurs than do standards. Spur-type trees remain 30 percent smaller than non-spur strains grafted onto similar rootstocks.
Prune apple trees to maintain a strong framework that supports the weight of the crop, and to maximize the number of spurs, which bear the fruit.
Pruning a Central-Leader Tree
Although a mature tree can easily be maintained at the desired height and spread, it will be necessary to prune regularly to restrict top growth. If top pruning is neglected, the vigorous upright shoots, which receive maximum sunlight, will grow faster than those below and distort the productive shape.
When the tree reaches a convenient height for harvesting and spraying, restrict further growth but still maintain the tree’s vigor. Each year during the dormant season cut all one-year-old laterals off the central leader. Then head the leader by one half of the previous year’s growth. Apical dominance will be restored below the cut and then new, upright-growing shoots will form from the dormant or adventitious buds. Remove any water sprouts and suckers.
As the tree matures it will be necessary to thin limbs to allow sunlight to penetrate throughout the tree. If the top tiers become overgrown with large branches, remove them rather than prune many smaller branches. This measure temporarily limits yields on the upper scaffolds but the lower tier becomes more productive.
Pruning a Vase-Shaped Tree
First, remove any damaged or broken branches. Next, thin back to a lateral any branches that are crossing the center of the tree. It’s important to keep the center open to allow light to penetrate to the interior. Thin it out if it is becoming overgrown. Head back some of the new growth to make the branches stronger.