Gary Moulton & Jacky King, WSU Mount Vernon Research & Extension Unit
Fruit trees need pruning for two primary purposes: to establish the basic structure, and to provide light channels throughout the tree so that all the fruit can mature well. A well pruned tree is easier to maintain and to harvest, and adds esthetic value to the home garden as well, but the primary reason for pruning is to ensure good access to sunlight. Did you ever notice that the best fruit always seems to be in the top of the tree? It’s true, because that’s where the most light is available. Training a tree that is open to the light, and easy to care for and to harvest, is the main consideration to keep in mind when pruning, whatever system you are using.
Most pruning can be handled with 3 tools: a hand pruner, a long-handled lopping shears, and a pruning saw. Either bypass or anvil-type pruners can be used, but a bypass-type is better for close pruning such as is necessary on young trees. Some prefer the folding saw for its handiness but non-folding types are good also. A number of accessories are useful in tree training. Either spreaders (different lengths can be made or purchased) or weights that clip to the branches can be used to bend branches to a more horizontal position, so they will begin fruiting earlier. Limbs can also be tied down using ground clips (hop clips).
The two types of pruning cuts you can make are thinning and heading. Thinning is removing an entire shoot, branch, or limb, back to the point where it originated. Thinning cuts are the ones you should use most of the time, because they tend to open up light channels throughout the tree. Often just thinning out the limbs that are crowding or crossing over does an effective job of opening up the tree. Heading is removing part of a shoot, branch, or limb (up to 1/3 to 1/2 of its length). Heading cuts encourage growth of side branches at the point of the cut, from the part of the branch that remains. Heading should be used primarily for establishing branches in young trees. Leaders or future scaffold branches can be headed to cause laterals to branch out. In most cases heading should be avoided, as it can result in a tree overcrowded with shoots that close off light channels and reduce productivity. When heading is necessary, such as to shorten and stiffen up a long bare branch, make the heading cut into older wood, as this results in less regrowth.
Pruning is done primarily in the dormant season (November 15–April 15), so when looking at a shoot or branch to decide whether to thin or not, try to picture the branch as it will be when full of leaves in the summer, and eliminate shoots that will be too closely spaced. Keep in mind the key phrase: When in doubt, thin it out! Make most of your cuts thinning cuts.
The training systemsmost used in pruning fruit trees are the Open Center, Central Leader, and Trellis (Espalier). In our area, as leftovers from earlier orchard methods, we also see many old trees pruned in the Umbrella method.
The Open Center or Vase type pruning is well adapted to the stone fruits that have a spreading habit. Peach, nectarine, apricot, cherry and plum are usually pruned as open center trees. In this system, at planting the tree is headed at the point where the future main branches will be established, and three to five of the branches are selected to form the main limbs, or scaffolds. In selecting future scaffold limbs, remember to allow clearance for lawn mowers, etc. Any limb will always be the same height above ground where it branches out from the trunk, no matter how large it gets, so be sure it doesn’t start out too low. Ideally scaffolds should be spaced evenly around the trunk and be of approximately equal vigor, but the more vigorous branches can be trained outward using spreaders to shape the basic framework of the tree in its first and second years.
As the tree matures, pruning should concentrate on keeping the center open by eliminating water sprouts, sometimes called “suckers,” that grow straight up from the main limbs, and providing good spacing and access to light along each of the scaffold branches. Peaches and nectarines bear fruit only on one-year wood, that is, the shoots that grew the previous season produce this season’s fruit. Half or more of each season’s new shoots usually need to be thinned out, to prevent crowding and make room for fruit to grow. Some branches on mature trees may need to be headed back if they spread too far, but be sure to thin the resulting shoots in the following year so that lower branches are not shaded out by excessive growth in the tops. Thin out large diameter shoots in the upper part of each limb.
The Central Leader is well adapted to trees that have a naturally upright growth habit , which includes apple, pear, cherry and some plums. This is the best system for trees on dwarf rootstocks. If trees already have developed side branches before planting, only the leader needs to be lightly headed. Side branches should be selected to form the lowest or main scaffold, and trained outward to a 45 degree angle with spreaders or tie-downs. Any branches that compete with the leader in vigor, or that would crowd the chosen scaffold branches, should be thinned out. Smaller branches can be left to set fruit, and should not be headed.
As the tree matures, select a second scaffold, 24″–30″ above the main scaffold, and train it similarly, only training to a flatter angle (about 60 degrees from the vertical). A top scaffold can be developed in the third or fourth season. The ideal profile is something like a simplified Christmas tree – a triangular shape wide at the bottom and narrowing at the top. In the top of the tree, thin out the most vigorous shoots, and keep those that are not so vigorous. Never allow the upper scaffolds to overgrow and shade the lower ones, and prune out large diameter upright- growing branches. Try to maintain about 60% of the tree’s total volume in the lower scaffold area. This provides good access to light throughout the tree, and makes for easy care and picking
Trellis training is similar to the central leader, only in a more 2-dimensional framework. Choosing a tree on the right dwarf rootstock is important, so that the tree doesn’t outgrow its space. The classic espalier is a more painstaking variation, but one that will reward the home gardener’s artistic efforts. A simplified trellis system is increasingly used by commercial orchards, particularly apple growers, to maximize fruit production per unit area, and to provide better exposure to sunlight for high fruit color and quality. The best alignment for a trellis is north-south, so that both sides get good exposure to sun. In setting up the trellis, the first wire is usually about 30″, and the top wire usually at 6 or 7 feet, but fruit trees are quite adaptable and can be trained to a number of different designs.
The key element to emphasize with all of them is that the less actual pruning you do, the better. The wires allow for branches to be bent down and tied in position, either horizontally as in the classic espalier, or at a 45 degree angle from the trunk. Very little cutting should be done, and then only to remove shoots and branches that are growing in the wrong direction (at right angles to the trellis) or are too crowded. In young trees, the leader should be headed to produce side branching at each level, until the main trunk reaches its desired height. After that, growth should be controlled by bending the branches to encourage early fruiting, and thinning out any shoots that are too vigorous.
Umbrella trees are usually older trees (some up to nearly 100 years old), originally planted in yards and homesteads when the modern size-controlling rootstocks were not yet available. They were pruned to an umbrella shape to keep trees that would normally reach 40 feet down to a manageable height. An established umbrella tree has as its basic framework one set of main scaffold limbs that are horizontal and are also the apex of the tree. Fruit bearing branches grow outward and downward from these main limbs, and clumps of water sprouts shoot upward.
Keeping these water sprouts thinned out is the key to maintaining a productive umbrella tree. About 80% of the water sprouts that emerge each year should be thinned out. The largest and most upright should be removed, leaving the smaller ones well spaced, much as you would thin a row of corn. These remaining sprouts can be positioned by bending and tying them to encourage more fruit buds. Don’t head these water sprouts, as it only stimulates more shoot growth and reduces fruiting.
In the rest of the tree, thin out weak branches, particularly those that are shaded by an overhanging branch. Areas of the tree that get little or no access to light will weaken and die, so try to make sure that all fruiting areas of the tree are pruned to let light in. When a tree has been left unpruned for many years, it is sometimes best to take 2–3 years to get it back in shape, rather than try to do it all at once. Start by looking at the basic structure of the tree and choose two or three major branches to eliminate completely – ones that will open up central areas of the tree to light. Try to visualize what the tree will look like without those branches. The next year, look again, and repeat the process. Follow up by thinning out water sprouts, and maintain the tree’s new shape with regular fine-tuning of the branches that develop.
Pruning: Both A Science And An Art
In a home garden no tree exactly fits the textbook training system. The science of pruning a tree means being aware of how light affects its growth, and how its structure develops over time. The art lies in pruning a tree so that the balance of growth and productivity is esthetically pleasing to you. Put aside any fears of making a mistake, and just keep in mind the purpose you are aiming for: a tree that is well balanced between growth and production, easy to manage, and open to the light and air. Until they gain some experience, most people tend to prune too little, and too timidly, rather than too much. Often you can make one or two big cuts to thin out a large, crowding branch and have a better result (for you and the tree) than from a dozen cautious little nibbles that don’t solve the problem. Think of it as a living sculpture, with many light channels flowing throughout its structure, which will reward your efforts with a bounty of tasty, good quality fruit
For anyone interested in learning more, a detailed 55-minute video Easy Steps to Fruit Tree Pruning can be obtained by calling 360-445-5483. Also, pruning workshops are included annually in the February/March Open House and Field Day held at Mount Vernon research station.