Do you need to repair a broken tree? Did your contracted landscaper (or you) bang the ride-on mower into your eighty-year old yellowwood? Did the mower grind up some pretty important surface roots? Repair grafting is laborious, but for a special tree with a major wound from winter splitting, animals (like buck rub or rodent chew), or power tools, it may be worth it to you.
Basic Idea of Repair Grafting
If you’ve ever noticed an old wound on a tree, from impact damage or a removed limb, you might have noticed rolls of “flesh” on the rim of the scar. When wounded, woody plants can heal only from the outside in because the actively dividing cambium is absent from the wound site, and present only at the edges.
Trees don’t truly heal as we do; rather, they grow over the dead wood in a wound with healthy wood. Working from the edges to the middle, this takes time, many years for large wounds. This is why when we make clean pruning cuts, we try to keep the wound as small and clean-cut as possible.
You wouldn’t do it for every wound on every tree, but for high-importance “specimen” trees, repair grafting can help along the healing process by sticking additional healthy wood onto and around the damaged site, where it can expand and cover the wound faster.
Inarching is a way to repair lower wounds on trees, including wounds to the roots. You can even replace the entire root system, done when you want to switch a mature plant to a new rootstock.
By inarching, small plants near the base of the tree have their tops joined to the trunk where they fuse into the wood, thereby providing a new root system and bridging any low damage.
Bridge grafting is a way to speed the healing of wounds on the trunk of a tree. Damage caused by buck rub, rodent chew, and impact with machinery are some examples of times this may happen. Proper pruning cuts, even to larger limbs, should not need repair with bridge grafting.
In bridge grafting, an evenly-spaced set of twig-sized scions, often from the plant itself, have their tops and bottoms inserted and nailed into the top and bottom of the wound. These fuse to the plant and, as they grow, expand and fuse to each other as in a natural approach graft, rapidly sealing the wound.
When two limbs have a weak crotch or other poor attachment one needs to be pruned off or braced before it splits out and leaves a large, ragged wound for disease to infect. Bracing can be done with a cable by a skilled arborist, where branches are essentially tied together with an artificial material, but artificial bracing has fallen out of favor as a sound arboricultural practice.
An alternative in the right circumstances is to use a woven “rope” of flexible scions, with each end grafted to the interior of the crotch. This is the graftage known as bracing. Instead of a man-made cable, which breaks down in the sun and weather over time, a rope of living scions grow, fuse, and strengthen.
Bracing is used particularly in orchards, where wood is often weak and depended upon to hold very heavy weights of large fruit.
Hartmann, Hudson T. and Dale E. Kester. Plant Propagation Principles and Practices, 7 ed. 2002.