Structural Pruning

Structural pruning improves the form of a tree by suppressing branches that are competing with the dominant leader. The objective is to prevent all branches and stems from growing larger than about half the diameter of the trunk. Young trees respond quickly to structural pruning. Changes in branch diameter relative to trunk diameter (aspect ratio) brought about by structural pruning are slower to manifest on medium-aged and mature trees than on younger trees because the core trunk and branch structure has already been established. Prune often and begin at planting.

Goals of structural pruning:

1. Develop and maintain a central leader.

2. Identify the lowest branch in what will become the permanent crown.

3. Prevent branches below the permanent crown from growing larger than half the trunk diameter.

4. Space main branches along the central leader.

5. Reduce vigorous upright stems back to lateral branches.

1

Current tree form demonstrates multiple co-dominant leaders and an out-of-scale lower branch

2

Current tree form demonstrates multiple co-dominant leaders and an out-of-scale lower branch

3

Current tree form demonstrates multiple co-dominant leaders and an out-of-scale lower branch

4

Current tree form demonstrates multiple co-dominant leaders and an out-of-scale lower branch

Step-by-step:

Identify the best candidate for a dominant leader. It should be in the center of the crown, and free of cracks, openings, mechanical damage, large pruning wounds, cankers or other defects that could compromise its strength.
Identify the stems and branches that are competing with this stem. This includes stems larger than half the diameter of the trunk, and large vertical growth other than the central leader.
Remove competing stems and branches back to the trunk, or subordinate by shortening them with a reduction cut. Be sure to remove branches that are clustered together and growing from the same point on the trunk. Ideally, only one large branch grows from one position on the trunk. Inspect for and remove any branches that inclusions, illness, or weak attachment.

Go back: Pruning Cuts

Next Page: Raising the Crown

Pro Tip: Pruning a young tree

Be prepared to develop good structure after planting if there are few nurseries that carry a particular species with suitable trunk and branch structure. This can begin when the tree is planted. When you see that pruning is needed to correct some trunk or branch defects on a recently planted tree, and you will not be able to prune the tree for several years, prune it at planting to correct the problem. If you wait, it may never be pruned correctly. Long-term health will be enhanced with improved structure.

Even small diameter (pencil size) stems that are the same size as the leader can occur in the top half of the crown on high-quality nursery stock. These could eventually develop into a group of codominant stems if they are not pruned at planting. Some pruning at planting is almost always necessary because it is unreasonable to ask growers to prune every tree with one perfect single leader to the very top of the crown. Last but not least, always check roots at planting and prune to correct circling roots and other root defects that could impact future health.

Tree on the left was planted into the ground several years ago. Notice the small current-year stems at the very top of the tree. Photograph above shows the tree five years later with codominant stems growing from what was the top of the original nursery tree.