The practice of removing a young tree’s lower branches, often referred to as “raising the crown” or “limbing up,” significantly shapes the tree’s future strength and appearance. This modification is a structural choice that directly impacts how the tree allocates its energy and develops a strong trunk. The correct approach depends entirely on the tree’s age, establishment, and the specific method used. Making this change too early or incorrectly can permanently damage the tree’s ability to support itself in high winds.
The Trade-Offs of Removing Lower Branches
A young tree relies heavily on its lower branches for developing a sturdy trunk, which creates a conflict with the desire for clearance. These lower limbs are important for photosynthesis, providing the energy needed for both root and stem growth, especially in the early years. Removing too much foliage too soon starves the tree of this energy source.
The movement of lower branches in the wind stimulates the trunk to grow in thickness, a process known as developing trunk caliper and taper. This gradual widening allows a tree to withstand high winds without snapping. Removing these branches prematurely results in a weak, spindly trunk that is more susceptible to failure as the tree matures.
Despite the biological benefits of keeping them, lower branches often create practical problems for homeowners. Common reasons for removal include providing clearance for walking paths, mowing equipment, or vehicle traffic. They are also removed for aesthetic reasons, such as revealing a clean trunk line or opening up views across the landscape. The goal is to balance these practical needs with the biological requirement for structural development.
Timing and Selection: When to Start Limbing Up
Pruning should not begin immediately after planting; a young tree must first overcome transplant shock and establish a vigorous root system. Arborists generally recommend waiting at least two to three years after planting before attempting any major structural pruning. This initial period allows the tree to focus its energy on growth rather than wound recovery.
When pruning begins, the most important rule is to maintain a high live crown ratio, meaning a majority of the tree’s height must be covered in foliage. The “two-thirds rule” suggests that at least two-thirds of the total tree height should have live branches to ensure proper trunk taper and health. Removing more than one-third of the total live canopy in a single year can severely stress the tree and must be avoided.
The first branches to remove should be the smallest, weakest, or those with narrow angles of attachment to the trunk. Many lower branches are considered “temporary” and should be retained for a few years to contribute to trunk growth and shade the bark. Rather than removing these temporary branches entirely, shorten them to reduce their length and slow their growth, encouraging the main leader to grow taller. This slow, gradual removal process over several seasons minimizes stress and allows the tree to compartmentalize wounds effectively.
Precise Techniques for Safe Removal
The method used to cut the branch is as important as the timing, since an incorrect cut can leave a large, unhealable wound on the main trunk. The cut must be made just outside the branch collar, the slightly swollen ring of tissue where the branch joins the trunk. This collar contains specialized cells that facilitate wound closure, and leaving it intact allows the tree to naturally seal off the wound.
For any branch larger than about one inch in diameter, the three-cut method must be used to prevent the branch’s weight from tearing the bark down the trunk. The first cut is a shallow undercut made on the bottom of the branch, about a foot away from the trunk, to prevent bark stripping. The second cut is made further out, cutting down from the top to remove the majority of the limb’s weight.
The third and final cut removes the remaining branch stub just outside the branch collar, ensuring a clean surface for the tree to seal. Using sharp, clean tools, such as bypass hand pruners, loppers, or a pruning saw, is important to make precise cuts that heal quickly. Avoiding wound paints or dressings is recommended, as research shows they often delay the tree’s natural healing process.