What is structural pruning? Ed Gilman from the University of Florida explains:
"Many shade trees in the forest grow straight, tall trunks as they compete with neighboring trees for sunlight. In the landscape, however, the abundance of sunlight all around the canopy encourages trees to develop multiple, competing trunks or leaders. This type of structure is susceptible to mechanical breakage and can reduce life expectancy. But trees with one dominant leader and small well-spaced branches, like trees in the forest, are less likely to suffer this type of mechanical failure. The dominant leader structure also makes trees better able to retard the spread of decay within the tree."
At Acorn, we love to prune young trees for proper structure early and regularly so that they'll have the best possible chance for a long, healthy, and safe lifespan. Let Acorn shepherd your trees through their awkward adolescent years into beautiful, stable, mature trees.
Problem - Before pruning, the young to medium-aged tree has three developing leaders or codominant stems (a, b and c). These are likely to develop into multiple leaders, which are considered weaker than trees with one trunk. Large maturing trees usually perform best and last longest if they grow with one main leader. Structural pruning helps the tree develop one main leader and one trunk.
Solution - Reduce the length of (subordinate) leaders 'a' and 'c' using a reduction cut to encourage leader 'b' to grow faster. This will help leader 'b' become the dominant trunk by slowing growth on leaders 'a' and 'c' and allowing more sunlight to reach 'b'. In most cases on large-maturing trees, branches in the lower 15-20 feet of the tree should be kept smaller than half the trunk diameter using this technique.
Solution - This moderate pruning treatment is similar to the light pruning treatment. The main difference is here we are more aggressive. Larger holes are left in the canopy following moderate pruning. This might be appropriate if trees cannot be pruned for several years, or if they might never be pruned again. Up to about 40% of foliage could be removed on young trees, if necessary.
1-3 years in the landscape, under 4" diameter, up to 12' tall
3-5 years in the landscape, 4-6" diameter, up to 16' tall
5+ years in the landscape, over 6" diameter, over 16' tall