Subordinating a Codominant Leader on a Young Shade Tree With a Folding Pruning Saw: Shorten or Remove at the 2-Inch and 4-Inch Marks

Young shade tree with a shortened competing stem and a folding pruning saw

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A young maple or linden that forks into two equal trunks looks full and balanced for a few years. It is also building the weak, bark-filled union that splits in a storm once the tree is big enough to hit the house.

How do you fix two competing leaders on a young shade tree?

Pick the straighter, taller stem as the leader. Shorten the other one with a reduction cut back to a smaller side branch so it grows slower, or remove it if it is approaching 2 inches thick. Above about 4 inches, shortening is usually safer than removal.

Colorado State University Extension's structural pruning guide for young shade trees calls codominant trunks a major structural defect. It says to remove a competing leader that is approaching two inches in diameter, and to shorten one larger than four inches rather than risk exposing heartwood.

University of Florida IFAS's plan for training shade trees says to subordinate all but one codominant stem. It also says to keep branches under half the trunk diameter and maintain a live crown ratio over 60 percent.

Shorten or Remove: Size Guide

Competing leader CSU guidance
Under 2 in., equal size, no collar Shorten so a collar can form
Approaching 2 in. Consider removing it
2 to 4 in. Weigh size, dose, and structure
Over 4 in. Shorten rather than remove

CSU bases the choice on branch sizes, how much of the pruning dose the tree can afford, and the tree's branching structure. Its guide cites the ANSI standard of no more than 25 percent of a healthy tree's foliage removed in a year.

How a Reduction Cut Subordinates a Stem

CSU says a shortened leader has fewer leaves, so it grows more slowly while the uncut leader gets more light and speeds up. Over a few seasons, the cut stem becomes a branch instead of a rival trunk.

A reduction cut takes a stem back to a smaller side branch that is still growing. Cut just above that side branch, and tilt the cut slightly on an upright stem so rain runs off.

Materials and Tools

  • 10-inch curved folding pruning saw
  • Bypass hand pruners for small side shoots
  • A sturdy step ladder rated for your weight, used on level ground
  • Safety glasses and work gloves
  • Rubbing alcohol and a rag for wiping the blade between trees

Pruning Steps

  1. Pick the leader. Choose the most vertical or tallest stem as the one you keep.
  2. Check for included bark. Look for bark that rolls smoothly into the fork, which CSU says makes a much weaker union.
  3. Measure the rival. Gauge its diameter to decide whether to shorten or remove it.
  4. Find a side branch. For a reduction, choose a smaller side branch on the rival stem well below its tip.
  5. Cut. Saw straight across just above that side branch, angling slightly on a vertical stem.
  6. Use three cuts on heavy pieces. Undercut first, then cut from the top farther out, then make the final cut.
  7. Stop at the dose. Keep the total foliage removed within the CSU guidance.
  8. Recheck next year. Shorten the rival again if it is still keeping pace.

Mistakes and Hazards

  • Topping the leader you meant to keep
  • Removing a rival over 4 inches thick and leaving a large wound
  • Taking too much foliage in one year
  • Pruning hard on a tree that is already stressed or declining
  • Reaching from a ladder with a saw instead of moving the ladder
  • Working near power lines; call your utility or an arborist instead

For keeping the trunk safe while it grows, see caging young yard trees against buck rubs. A newly planted tree may also need staking with two stakes for its first season.

Voles chew the bark at the base of young trees in winter. The hardware cloth mesh size and gauge guide covers the mesh used for trunk guards.

FAQ

When should I start structural pruning?

UF IFAS says to begin pruning at planting and continue for 25 years, with about seven prunings in that span.

Why is a codominant union weak?

CSU says the union between codominant leaders does not form a branch collar and often has included bark, so the wood does not knit together.

Can I shorten a leader in two stages?

Yes. UF IFAS notes you may have to shorten competing leaders in two stages when there are more than three leaders.

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