How to Repair a Broken Tree with Grafts

Grafting a tree branch
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Maybe your landscaper (or your husband) rammed the ride-on mower into your Kentucky yellowwood tree. Or, you accidentally ground up a few fairly important surface roots yourself. Trees can also sustain damage due to winter splitting from heavy snow loads or animal damage (like buck rub or rodent chew). Whatever the cause, tree surgery may be needed. Tree grafting is a laborious undertaking, but for a special tree with a major wound, the task may be worth it to you.

Tree Grafting Basics

If you inspect an old wound on a tree—resulting from impact damage or a broken limb—you might notice rolls of “flesh” on the rim of the scar. When wounded, woody plants heal from the outside in because the actively dividing cambium (or skin) is now only present around the edges. The tree then attempts to grow over the deadwood in the wound, replacing it with healthy wood. Working from the edges to the middle, this can take many years to complete. For this reason, it's important to make clean cuts when pruning to keep the resulting wound as small as possible.

Grafting involves placing a makeshift Band-Aid over the wound to form a bridge that the cambium can adhere to. Grafting is usually only required for a large wound, aiding in the healing process and covering the damaged site. The result yields a faster recovery time and prevents insect damage or disease from moving in.

Bridge Grafting

Bridge grafting is one of the most common ways of healing of wounds on the trunk of a tree. In bridge grafting, an evenly-spaced set of twig-sized scions (or bridge wood) is obtained either from the tree itself during a prior growing year or purchased from a nursery. To graft:

  1. First trim the loose bark from around the wound, creating smooth edges.
  2. Next, slice a few parallel cuts above and below the wound, peeling back the bark to make flaps.
  3. After that, work the end of each scion under the flaps and nail the ends in place with small brads to secure them.
  4. Lastly, cover the grafts with grafting wax to prevent the wound from drying out and shave off any buds that form on the scion during the repair process.

Note: Depending on the size of the wound, you may need several scions to complete the bridge.

Inarching

Inarching is a way to repair wounds that reside on the lower part of the tree, including a wound to the root. You can even replace entire root systems by using this tactic.

Inarching involves taking the small plants (or suckers) that reside at the base of the tree and joining them to the trunk in a similar fashion to bridge grafting. For this process:

  1. Select suckers that are at least a 1/4 inch in diameter.
  2. Cut the sucker so that it's a 1/2 inch longer than the wound area.
  3. Create a flap in the tree's bark, similar to the flaps used in bridge grafting, so that you can slide the sucker under it to create a girdle.
  4. Cover the area with grafting wax and protect the tree with a cage or cylinder to prevent future damage.

Bracing

The last type of wound repair is used when two limbs on a tree develop a weakened crotch or poor attachment point. Bracing needs to then be implemented to secure the branches that could otherwise split the tree, leaving a large, ragged wound. Bracing is usually performed by a skilled arborist and involves tying two branches together with either an artificial material, like a cable, or a woven “rope” made of flexible scions grafted to the interior of the crotch.

Instead of using a man-made cable, which can decompose due to sun and weather, a rope of living scions grows into the tree's structure, fusing and strengthening the organism. Bracing is used particularly on orchard trees where weak branches may yield heavy loads of large fruit.