Source: Richard Jauron, Iowa State UniversityWilly Klein, ISU Extension
One of the most important management practices for landscape trees is pruning. When done properly, pruning can improve the health and structure of trees, as well as provide a safer environment for people, pets and property. The best time to prune is in mid to late winter, which allows the tree to respond to the wounding early in the spring. Iowa State University Extension and Outreach horticulturists discuss proper pruning techniques. To have additional questions answered, contact Hortline at 515-294-3108 or email firstname.lastname@example.org.
Cut off the branch just beyond the branch collar and branch bark ridge. The branch collar is the swollen area at the base of the branch. The branch bark ridge is the dark, rough bark ridge that separates the branch from the main branch or trunk. Pruning just beyond the branch collar and branch bark ridge retains the tree’s natural defense mechanisms and promotes compartmentalization and callus formation.
Do not make flush cuts when pruning trees. Flush cuts are pruning cuts made as close as possible to the trunk or main branch. They destroy the tree’s natural defense mechanisms that promote wound compartmentalization and callus formation.
To prevent extensive bark damage, use a three-cut procedure when pruning branches that are greater than 1½ inches in diameter. Make the first cut 6 to 12 inches from the main branch or trunk. Cut upward and go about one-third of the way through the branch. Make the second cut 1 to 2 inches beyond the first. Saw downward from the top of the branch. As the second cut is made, the weight of the branch will cause it to break at the pivot point between the two cuts. (The initial, bottom cut prevents the branch from ripping off a large piece of bark as it breaks.) Make the final cut just beyond the branch collar and branch bark ridge.
Do not apply a pruning paint or wound dressing to pruning surfaces. The application of a pruning paint or wound dressing does not prevent wood decay and may actually interfere with the tree’s natural wound responses. Oak trees are an exception to the no paint recommendation. To prevent the transmission of oak wilt, oak trees should not be pruned in spring and summer. If an oak tree needs to be pruned during the growing season, for example to correct storm damage, immediately (within 15 minutes) paint the pruning cuts with a latex house paint. Winter (December, January and February) is the best time to prune oak trees in Iowa. There is no need to paint the surfaces of pruning cuts when oaks are pruned in winter.