When apple trees are pruned yearly, it becomes a quick and routine job. When the trees are left for a number of years, more needs to be removed making the job harder and more time consuming. Apple trees should be pruned when they are dormant. The goal of pruning an apple tree is improve fruit production, more and larger fruit.
If the apple tree is mature, look to see how it was originally pruned. Older trees were often pruned with an open center or vase is style with the central leader is removed at 30 – 26 inches (.75 to 1 meter) from the ground. Low side branches are pruned to grow tall and wide with an open center making the tree easy to climb and the fruit readily assessable. At present time, young trees are rarely pruned using this method as the open centers often results in sunscald from the heat of the early spring sun reflecting off the snow.
Today pruning an apple tree by modifying its central leader is considered acceptable practice. The central leader is removed once 7 - 12 strong lateral or side branches have formed. Removing the top of the leader reduces the tree’s height, encouraging the tree to spread outwards. In this method, young trees are trained to a central modified leader with branches radiating in 4 directions; like an X. Ideally there should be 3 different levels of branches growing from the main leader. Each level should be at least 6 in. (15 cm) higher or lower than other branches.
Space between the branches insures that air circulates throughout the tree and branches do not rub. The tree is also pruned in the shape of a pyramid. Shorter branches at the top, ensuring the bottom branches receive sunlight.
Apple trees that are grafted on semi-dwarfing or dwarfing rootstock do not need their central leader removed as they will not reach an unmanageable height. Instead, these trees are pruned to remove excess branches and foliage which encourages the tree to put its energy into the fruit.
When pruning apple trees, start by removing all water sprouts, suckers and dead wood. Water sprouts are new branches that grow 2 or 3 feet upwards in a season. Suckers are new growth that comes from the roots not the grafted part of the tree. If left intact, the suckers will outgrow the grafted section of the tree, using all the nutrients, which eventually will kill the tree above the graft.
Next eliminate crossing branches by removing the branch with the least desirable characteristics; pointing towards the center of the tree, torn bark, weak angle or smaller in diameter.
Remove branches that duplicate or hang under other branches as the fruit on these branches will not be in the sun
Remove or modify narrow angled branches as they produce weak unions and are likely to split under stress of a crop of apples or a heavy snow. Young branches can be trained to grow at a wider, ideally 90˚angle by either pulling the branch down with a rope which is attached to the ground or by attaching a milk jug or water bottle to the branch and filling it with enough water to cause the branch to go downward to the desired angle. Remove the weights or rope when the branches hold the desired shape.
Prune back the upper and outer branches to keep the tree manageable
Fruiting wood which is thicker and grows slower forms on growth over 2 years old. As the tree ages, remove older fruiting wood from the center of the tree and keep the new wood closer to the end of the branches where the apples will receive more sunlight and be easier to pick.
When pruning, keep an eye of the pile of wood that has been removed from the tree. Remove over a ¼ of the tree in a year and the tree will become stressed and put forth numerous suckers and watersprouts.
Remember to set aside time on a warm day when the trees are dormant annually to prune the apple trees. The result will be fewer but lager fruit.
Linda Tomlinson is a horticulturalist that lives close to Rocky Mountain House. She can be reached at your_garden@hotmail.com