Take care when pruning young trees
By Tivon Feely
Iowa State University Extension
Landscape trees need proper care throughout their lives, and one of the most important tree management practices is pruning. Pruning is more than just indiscriminately removing branches. When done properly, pruning can improve the health and structure of the tree. Proper pruning includes knowing which branch to remove, when to do it, and how to minimize damage to the tree.
The main reason to prune young trees is to develop a good branch structure, and the first 15-20 years of a tree's life is the most critical time to prune to achieve good branch structure. The best time to prune is in mid to late winter (January-March). Pruning during this time of the year allows the tree to have a full growing season to seal over the wound.
If pruning must be done at other times of the year, avoid pruning during the spring from bud break through leaf expansion and during the fall leaf color season. Pruning during those times may reduce the vigor of a tree. Oak is a species where timing of pruning is critical. The pathogen that causes the oak wilt disease can be transmitted through open wounds by a small sap-feeding beetle. For this reason, avoid pruning oaks from March through September.
Limit pruning of newly planted trees to the removal of dead and broken branches or the correction of multiple leaders. Leave the temporary lower branches on the tree until they reach 1 inch in diameter to increase trunk growth and root development. Concentrate efforts on removing crossing, rubbing, broken, diseased and weak-angled branches in the upper portion of the tree. Also, eliminate double leaders and basal sprouts. Remember pruning is an on going process throughout a tree's life.
Before making a pruning cut, identify the branch bark ridge and branch collar. The branch bark ridge is simply where the branch and trunk meet. The branch collar is the swollen area just under the branch. When removing a branch, use the three-cut method. The initial cut is made on the underside of the branch 6-12 inches from the trunk and about a third of the way through the stem. The second cut is made through the stem about 1 inch outside the initial cut. The second cut removes the weight of the branch preventing tearing. The last cut is made outside the branch collar.
Proper pruning will help enable young landscape trees to survive and thrive. For more information on pruning, consider reading Iowa State University Extension publication Pruning Trees and Shrubs (SUL 5). That publication is available at www.extension.iastate.edu/store .
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