Principles of Pruning, Part 2: Making a Good Cut

Pruning shade trees is important to keep the tree healthy and growing properly, and while there are many valid reasons to prune a tree, the three main reasons are for safety, health and appearance.

Dr. Jeff Iles, chair for the Department of Horticulture at Iowa State University, said that it is important to be vigilant when it comes to pruning to ensure a long life for your trees.

Lower branches on a young tree are vital; they help develop stem taper and the root system of the tree, but it is important to keep eyes on those branches, as they will never grow higher, and might be in the way someday.

When looking at a tree, Iles likes to see about 2/3 of the tree in branches, and said that proportion should be kept up for the entire life of the plant, while of course only pruning during the dormant season. Read more about why and when pruning should occur in Part 1 of this pruning series here.

Iles said that when pruning, using a three-cut technique is usually a successful method. The first cut should be on the underside of the branch about a third through the branch and 6 to 12 inches from the trunk, and the reason for this is to keep the bark from ripping down the side of the tree. The second cut is made on the top side of the branch, about one inch farther out. The branch will break at the pivot point between the two cuts.

The final cut is made just outside the branch collar, which is the flared base of most branches. This collar is an important barrier, or protection zone, that prevents the spread of decay in the trunk. Pruning cuts that injure or eliminate the collar destroy the protection zone, leaving vulnerable tissues open to invasion and infection. Therefore, the proper pruning cut should be made to the outside of the branch bark ridge and collar. Flush cuts must be avoided because they violate the protection zone and leave large wounds that are difficult for trees and shrubs to defend.

For Part 3 in this series, click here.

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