Growing Together: How to prune an apple tree
A primary reason for pruning fruit trees is to let more sunlight and air inside the tree. The sunlight prompts more flowers to form lower on the tree, yielding more fruit within easy reach.
Most apple tree owners know our fruit trees should be pruned. But when we’re standing in front of the tree with pruning shears in hand, knowing how to begin the surgery can feel intimidating.
Apple tree pruning isn’t as complicated as it might seem once we understand what twigs and branches to remove. We’re now entering the prime pruning window of opportunity, after the coldest winter weather is likely past and before spring warmth causes growth to begin.
Pruning while apple trees are dormant is the traditional time, from about mid-March through mid-April, depending on the year. You can easily see branch structures while trees are bare, and trees won’t waste energy producing new growth that ends up being pruned away.
Fireblight disease bacteria are inactive now, so spreading the bacteria during the pruning process is less likely during the dormant season. However, there is an alternate time for apple tree pruning to better reduce the chance of another major disease, which I’ll address later in the column.
A primary reason for pruning fruit trees is to let more sunlight and air inside the tree. The sunlight prompts more flowers to form lower on the tree, yielding more fruit within easy reach. Getting more sunlight and wind in the canopy decreases interior humidity and lessens disease.
Pruning also controls tree size. If left to their own devices, apple trees can become large, with the best fruits high on the outer perimeter where better sunlight encourages flowering and fruiting high on the tree.
Pruning levels out yearly fruit crops, reducing the tendency of some apple types to have boom-or-bust apple harvest cycles, where trees bear heavily one year, followed by no apples the next.
To begin pruning, several types of tools are needed. Handheld, shears-type pruners are meant to cut branches about pencil-sized diameter. Long-handled loppers are for branches about one-inch in diameter. For larger branches, a pruning saw is needed.
To decide where to begin, imagine the ideal, well-pruned, well-bearing apple tree. The shape favored by research is a pyramidal Christmas tree shape, with the lowest branches being the widest.
Pruned to this shape, all branches receive greater sunshine, which encourages more flowers and fruit lower on the tree. The shape is called a “central leader system” in which a single central trunk runs the height of the tree, with strong side branches, called “scaffold” branches, radiating outward.
On young trees, planted within the past few years, if there’s 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 a little older, around five to 10 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, and moving up the tree 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.
If your apple tree has never been pruned, reshape it gradually over several years, especially if your apple tree is overgrown and fruit is high out of reach. Remove about one-fourth of the tree’s height each year for four years, attempting to get the tree down to about 12 feet high. Prune branches back to side growth, never leaving stubs.
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.
I previously indicated the dormant season to be the traditional apple pruning time. However, Jim Walla, retired NDSU plant pathologist, now with Northern Tree Specialties, is a leading fruit tree authority, and he favors delaying pruning until apple trees begin active growth.
As Walla indicates, the risk of black rot canker fungus, which is by far the most damaging disease of apples in our area, is reduced by delaying pruning until trees have begun growth. Because the tree’s cell growth has become active at that point, pruning cuts will seal more rapidly, leaving less tissue open to invasion by the black rot fungus.
Walla’s observations about delayed pruning are well worth noting, as black rot canker disease kills many area apple trees every year.