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 Pruning 101: For the Home Orchard
Excerpt from The Apple Grower, by Michael Phillips
Pruning begins with knowing why you do what you do. Limiting a tree's reach is just one reason to thin out branches and make heading cuts. Pruning encourages fruit set and allows good air flow and sunlight penetration around the developing fruit. Old wood eventually needs to be replaced if the tree is to remain fruitful. The tree responds to different cuts in different ways, and an understanding of these variables is what will make you a good pruner.
Start with a vision of shape and lateral spacing. An orchardist will speak of maintaining a central leader within a framework of three scaffolds. Like a conifer, the base is kept broad and the top more upright to allow sunlight to reach the fruit buds on the lower branches. A scaffold consists of three to five branches radiating out from the trunk within a one- to two-foot span of the trunk. Having approximately three feet between scaffolds is a goal, with the first scaffold starting three feet or so above the ground on a semi dwarf tree kept to twelve feet high. Lower branches are too much in the "fungal zone" to produce high-quality fruit, and they often interfere with mowing. Training a tree during its first several years in the ground will get you much closer to the envisioned ideal than coming in years later to reshape the tree's framework to your liking.
Overly tall leaders, crossing limbs, and those branches growing back towards the center or with narrow crotch angles are the obvious ones to remove. A heading cut on a lanky leader will stiffen the remaining wood and encourage the lower buds on the clipped shoot to set a satisfactory top scaffold. Crotch angles are best dealt with at a young age - you want branches to radiate out from the trunk in the horizontal plane up to a 45-degree angle. Branches that develop with narrower crotches form a weak union with the trunk because of included bark, and years later, be it under a heavy fruit load or in an ice storm, severe injury to the trunk is likely when the branches split. Broken or infected branches should always be removed.
Focus on thinning out branches on each scaffold once the basic framework is in place. Excess branches up high block sunlight to lower limbs and to those precious fruit buds in the interior of the tree. Remove branches that don't hold to the horizontal plane and that compete with other shoots at the end of the scaffold branch. It's a delicate balance to leave enough fruiting spurs and yet not overcrowd those remaining and prevent them from receiving the sunshine and nutrients needed to grow large, beautiful fruit.
A proper pruning cut is made flush with the branch collar on the trunk so it can completely heal over. Leaving a branch stub is an invitation to disease and rot, as the uncovered dead wood will serve as a point of entry. Shearing off the branch collar removes the protective tissue that will form the healing callus. Generally, all cuts are made at the union of a branch to its parent limb. A heading cut made along the branch (out from the attachment point) stimulates lateral bud growth. Buds nearest this cut will be invigorated more and bend towards the vertical plane, but further back, the hormonal balance brought about by a heading cut will favor wider branch angle development. Large branch removal can result in rampant sucker growth in the healing tissue around the wound, which is best reversed by back-to-back years of summer pruning.
Dormant pruning should be done in late winter when the risk of sub-zero temperatures has passed. A branch cut stimulates cell activity at the wound, causing the tissues to lose hardiness for ten to fourteen days after the cuts are made. Prune the hardiest varieties on the more vigorous rootstocks first to lessen the possibility of such winter injury. Summer pruning in early August, particularly of water sprouts and when training young trees, encourages fruit bud development over vegetative regrowth. It also allows better sunlight penetration to the ripening fruit, resulting in better color and size. Summer cuts are best limited to branches with a diameter of one inch or less, which can fully harden-off before the winter months.
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