The most common damage to trees in home landscaping tends to be from cars hitting the lower parts of trees and trucks hitting higher on the trunk and the undersides of major limbs. Trees don’t heal as we do; when they are injured, the wood on the outside of the wound can only creep in year by year until it closes over. This is called compartmentalization of decay in trees, or CODIT.
When a tree you love has a big wound, the bridge graft is your best aid if you are willing to put the time and work into the job. It is a type of repair graft, not used to propagate plants but to supplement damaged vascular tissue.
When to Use a Bridge Graft
You might want to use a bridge graft if the tree is special and/or the wound is large. This graft takes a lot of work. It’s not worth it for small wounds that will heal well on their own, or trees without a major role in your landscape. If you do choose to use a bridge graft, do it during the active growing season. You need bark that will “slip,” and this is only possible during the active season of growth in spring through summer. Early spring is best.
What Is a Scion?
A scion is a young shoot or branch of a tree commonly used in grafting. This project uses scions from the damaged tree, if possible, to create a patch that is likely to hold, protect the tree, and heal the injury.
Equipment / Tools
- Grafting knife
- Chisel and mallet (if needed)
- Long nails
- Sealing wax
- Bow saw (if needed)
- Pole pruner
- One-year-old scions of 1/4 inch to 1/2 inch thick and long enough to bridge the wound
Trim the Problem Area
Trim the wound edges to a cleanly cut and smooth edge on top and bottom. Remove all ragged and dead tissue; the edges should be made entirely of live tissue.
Cut the Scions
A natural place to get scions is the young, last year’s growth of the tree you are working on. A pole pruner is your best friend here. Cut them to the correct length to bridge the wound, with slanting cuts on either end. The slants should go in opposite directions so that the scion now has a long side and a short side.
Cut Into the Bark
Cut pairs of slits distanced at the exact width of the scion, a pair just above the wound and a pair just below it. These slits should allow you to pry up a free end of bark to get underneath it.
Insert the Scions
The long end of the scion faces the tree. To work it in, pry up the bottom slit bark—possibly with a chisel—and firmly force the bottom of the scion into the tight space. Do the same to work the top of the scion into the top slit directly above. The scion is now firmly fixed in place, all parts touching or nearly touching the tree, not bowed out too much. Nail the ends in place.
Insert More Scions
Insert scions again, just as you did in the previous step. This time, however, you'll insert them laterally. This will create a grate of many scions spaced about 1 1/2 inches apart.
Complete the Repair
Wax all of the unions and the exposed wound wood. Perform standard aftercare for the new graft.