Pruning Primer - Thinning
Thin to Maintain Shape
Thinning is the complete removal of a branch back to another branch or to the main trunk. Thinning is almost always the most appropriate method for pruning most shrubs and trees. Thinning is used to control size while still maintaining a natural appearance. Thinning creates a more open plant and allows more sunlight to reach the interior and the ground beneath. Thinning cuts do not stimulate the growth of new shoots. Thinning cuts are used to maintain a neat, informal shrub with a natural shape.
Thin to Control Size
Use thinning cuts on shrubs and trees to control or even reduce size, and to allow more sunlight to penetrate and reach the ground below. You can dramatically reduce the size of a tree or shrub by cutting back the main trunk and some of the lateral branches to the next lower crotch with a smaller branch. This is called "drop crotching." The size of the remaining branch should be at least 1/2 to 2/3 the diameter of the branch removed, otherwise it might react like a heading cut and respond with numerous weak shoots emerging below the cut.
Thin to Increase Flowering
Woody plants that bloom on new growth, like crape myrtle, will have more and larger blossoms if thinned to remove smaller branches and twigs.
- remove excessive stems (suckers) that emerge from the base of the plant
- remove branches that point in toward the center of the plant
- remove small caliper branches and twigs
- remove lateral branches from ground to nearer eye level when trimming flowering trees
Thin for Health and to Increase Vigor
Thinning increases a plant's vigor by removing old growth and making way for young wood which flowers more profusely and is more resistant to disease. Certain situations call for "surgery" in order to maintain the health of the plant. This kind of thinning should be performed anytime of the year it is needed.
- when two stems cross and rub together one should be removed to prevent physical damage to the bark
- branches that are dead, damaged or broken should be cut back to make room for new growth
- branches that are diseased or infested with insects should be removed to lessen the chance of spread
- old branches should be removed to stimulate new growth which is more vigorous
Making the Cut
Never make cuts flush with the trunk or larger branch. Instead, always make pruning cuts a half-inch to an inch above the branch collar, a slightly bulging ring on the branch where it is attached to the trunk or to a larger branch. The branch collar produces the hormones that cause the wound to heal; be careful not to damage it.
Remove large branches in two stages to prevent accidentally tearing bark off the branch collar should the limb fall prematurely. First, remove most of the branch: Saw through the bark on the bottom side of the branch 6-10 in (15.2-25.4 cm) above the branch collar.
Next, finish the first cut from the top side of the branch.
Now the remaining spur, relieved of most of its weight, can be removed safely with the final cut, just above the branch collar.
A large branch was removed from this plum tree and the branch collar is healing over the wound nicely. No need for tree wound dressing!
Steve Christman 3/6/01; updated 12/26/03, 9/21/15