Trees are thinned, or pruned, to give them a more attractive or useful shape, to give them more vigorous growth, to eliminate diseased branches, and to increase the size and production of fruit. Knowing what to cut rests largely on knowing how the tree will respond when it loses buds or branches.
The Effect of Trimming
Thinning does not eliminate roots, so the strength and vigor of a new shoot depends on how many stems that you cut. If you just remove the tips of old growth, there will be shorter and less vigorous new growth. If you want more fruits that are smaller in size, thin sparingly. If you want fewer, but larger fruits, thin more vigorously.
If you cut the end of a young, vigorous branch, you will encourage lateral shoots up and down the branch. If you cut the branch back heavily, the one or two buds below the cut will grow rapidly. Thin lightly to develop a bushy, well-shaped tree. Thin heavily to encourage growth.
The last bud on a branch determines which direction the new shoot will grow. To thin a crowded interior, keep buds that point outward. This prevents shoots from crisscrossing through the interior of the plant. Remove branches that are crossing, broken or infested by branches.
Where to Cut
When you prune branches, choose those that are close to 45 degrees to the larger branch from which they are growing. When you remove a bud, the buds nearest to the cut will become the new growing points.
To shorten a branch, prune it back to a side branch. Cut a 1/2 inch above the bud. If you cut too close to the bud, the bud will usually die. If you cut too far away, the bud above the wood will usually die.
When you remove the terminal, or top, the nearest side buds will grow more than usual; the bud nearest your cut will become the new top. If you want more branches to grow on the side of your tree, cut the tips of all limbs.
Removing Thick, Heavy Branches
Cut heavy and thick branches as far as the collar at the base of a branch. The collar is the base of a branch at the trunk. It protects the trunk from decay that might be advancing down the branch. If you cut the branch flush to the trunk, you eliminate the trunk's natural protection, leaving it open to fungi, disease and decay.
When you cut a branch more than 1 1/2 inches wide, make a cut about a one-third of the way through the branch from 6-12 inches from the trunk. Make a second cut on top 3 inches out from the undercut. You have a stub that you can cut back to the collar.
Thinning versus Topping
When you top a tree, you cut it back to a few large branches. You will see vigorous growth for a few months, but topping leaves a tree open to attack by disease and insects. Windstorms can break off the bushy new growth.
It is better to thin a tree by cutting it back to its original shape, retaining its natural branching and making its interior more open.
Thinning Young Trees
The practice of removing up to one-third of the top growth of newly transplanted trees reduces the amount of leaves needed to generate plant energy. Thin only to maintain the shape you want and to shorten shoots that are extra vigorous. Don't remove limbs larger than 1 inch wide to avoid scarring the trunk.
Thinning Older Trees
Prune older trees when they are dormant. Limit your thinning to smaller branches that you can reach from the ground.