Trees that are healthy and structurally sound provide all the great benefits associated with trees

Structurally sound roots start when a tree is planted carefully in a site that provides the tree enough growing space. Structurally sound tree canopies start at the nursery, but must be maintained as a tree grows into the available space in which it’s planted.

Correct pruning, outside the branch collar, helps a tree grow quickly over the wound.
Correct pruning, outside the branch collar, helps a tree grow quickly over the wound.

Trees don’t outgrow their clothes like growing kids do, but they may “outgrow” the branch structure they have as a young nursery tree. Consider this: in order to create clearance for vehicles, signs, pedestrians, etc., branches on most newly planted medium-sized trees (maple or ash, for example) are pruned so that the lowest branch is eight or more feet off the ground. That means that most, if not all, of the branches on a newly planted tree will eventually be removed; they are temporary.

When trees are planted and left to grow without follow-up pruning, low branches, crowded branches, and branches with tight attachment angles start to cause structural problems. Structural problems lead to what arborists call predictable failures: broken branches or total tree failure from defects that could have been eliminated when the tree was young and its branches small in diameter.

Any pruning is a form of wounding, which can make a tree susceptible to insect and disease problems. It is best to prune small branches while a tree is growing vigorously so that the tree can grow around small pruning wounds. Delaying pruning until large branches grow out can be asking for a problem.

According to Dr. Ed Gilman, Professor, Environmental Horticulture at the University of Florida, there are six components of structural pruning:

  1. Develop or maintain a dominant leader
  2. Identify the lowest branches in the permanent canopy
  3. Prevent branches below the permanent canopy from growing too large
  4. Keep all branches less than one half the trunk diameter
  5. Space main branches along one dominant trunk
  6. Suppress growth on branches with included bark

Consider visiting Dr. Gilman’s website Landscape Plants to learn more about pruning shade trees in the landscape and structural pruning. You can even view growth animations of how trees look with and without the benefit of structural pruning.

DNR’s Urban and Community Forestry team is here to help. We offer pruning, planting, tree care and maintenance workshops for municipalities and tree boards. Call us at 360-902-1703, for more information, and to schedule a workshop in your region.

Prune outside the branch collar to avoid damaging trunk wood. Photo: USDA Forest Service - Northeastern Area Archive, USDA Forest Service, Bugwood.org
Prune outside the branch collar to avoid damaging trunk wood. Photo: USDA Forest Service – Northeastern Area Archive, USDA Forest Service, Bugwood.org
A good pruning wound looks like a donut, as it seals.
A good pruning wound looks like a donut, as it seals.