“Prune until it hurts, and then prune some more,” was the old saying repeated by North Dakota State University’s Professor Neal Holland as he taught apple tree pruning to us young horticulture students some 45 years ago.
We were so afraid of cutting away too much, but quickly learned that timidity prevents the proper pruning necessary to make trees more productive.
Why should we prune apple trees? The most apparent reason is to control height for easier picking. If left unpruned, apple trees can become large, with the best fruits high on the outer perimeter where better sunlight encourages flowering and fruiting. If left unpruned, large upper branches shade and overshadow lower branches. Proper pruning encourages fruit formation on lower branches where picking is easier.
Pruning also decreases disease by increasing air circulation through the tree as the canopy is thinned, removing overcrowded branches. And it helps trees bear fruit more evenly each year, leveling out the every-other-year heavy crop pattern of many apple varieties.
The best time to prune apple trees is late winter, after severe cold is likely past, but before new growth begins to sprout. March through early April is usually a good pruning window for fruit trees.
To decide what branches to prune, start by imagining the ideal, well-pruned, well-bearing apple tree. Research favors the “central leader system” in which a single central trunk runs the height of the tree, with strong side branches called “scaffold” branches radiating outward. The preferred shape is pyramidal, or Christmas tree-shaped, with the widest, outstretched branches lowest on the tree. All branches receive greater sunshine with this shape, which encourages more flowers and fruit lower on the tree.
Most apple trees fall into one of three categories: young and planted within the past few years; 7 to 15 years old and of fruit-bearing age; and older, overgrown trees. Let’s examine each pruning case separately.
On young trees, if there is more than one central leader, remove one to eliminate “V” branching at the top of the tree. Prune into a pyramidal shape with the lowest branches being widest, and shorten progressively as you move up. Always cut to a side bud or branch, never leaving empty stubs.
If an apple tree is about 7 to 15 years old and is currently a round globe, prune it into the pyramid shape described earlier. Start with the lowest branches, making them the widest. As you move up the tree, shorten branches in stair-step fashion until the top is the narrowest point.
Branches along the central trunk are often too close together on trees of this age. The main horizontal scaffold branches should be spaced 12 to 24 inches apart along the trunk. Remove excess branches back to the trunk, pruning just outside the raised “collar” where the branch arises from the trunk.
After shaping the tree and establishing a network of scaffold branches, prune out crisscrossing branches and branches pointing backward into the tree. Branches should radiate outward. Remove upward-pointing shoots, called watersprouts, from main branches. Remove sucker growth from the tree’s base, and any dead wood.
If your apple tree has never been pruned, reshape it gradually over two or three years. If your apple tree is old, overgrown and any fruit is high out of reach, a rejuvenation might help. Remove about one-third of the tree’s height each year for three years, attempting to get the tree down to about 12 feet high. Prune branches back to side growth, never leaving stubs.
Following steps in the preceding paragraphs, remove the clutter from inside the tree, such as branches that rub one another, and inward facing branches. Opening up the tree will allow more sunlight and air movement, which will improve fruit color and reduce disease.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at firstname.lastname@example.org or call 701-241-5707.