Dear Janet & Steven,
The snows kept us housebound for a while and we didn't use the front door. When we finally shoveled that walk, imagine our dismay to discover that our six year old Japanese red maple that is three feet high and up against the house has a split in the top crown. It looks as though the split can get worse, go down the entire trunk and then we will lose our precious friend.
Is there anything we can do to save it? My husband suggested drilling a hole through the sides and inserting a screw to pull the split together. Is this the way to save our tree? - P.M. -
Yes, bracing is a possibility, P.M. That means to insert a metal rod which will help hold a weak or split crotch together until several years of new growth encircles the problem area like like a layered fiberglas cast -- one that can never strangle the trunk or limb because the growing edge remains on its outside. The rod remains in the limb, beneath the new wood.
Do this work while a tree is dormant or fully leafed out. Don’t do it in spring as it’s leafing out because then the tissue just under the bark is slippery and easily damaged. Don’t do it in fall because a tree’s infection-prone as it drops leaves. So what I describe here should be done before March 1.
Carefully remove any snow from the split branches to reduce their weight. Gently draw them back together. This might involve installing crutch-like props under the limbs.
Buy a threaded rod from the hardware store, perhaps one half inch longer than the diameter of the trunk just below the split. Buy a pair of nuts and four washers to fit the rod. Make a hole for the rod 3 to 4 inches above the lowest part of the split. Drill through the centers of the two halves of the trunk, at right angles to the split. If you were able to close the split, drill the hole 1/16 inch diameter less than that of the threaded rod, which will then be screwed through the wood. If you must tighten the nuts to bring the limbs together, drill the hole the same size as the rod.
Before inserting the rod, cut the bark and cambium away from the hole in a circle just larger than the washer. This seats the washer against the wood rather than the bark, allowing new growth from the edges of your cut to more quickly cover the hardware.
Here's a diagram of that process:
Imagine this as the top branches of a small weeping tree, in profile (A) and in cross section (B). Each branch adds a ring of wood and bark each year. Where these rings have united, that wood holds the limbs together.
Above: When weight on one branch stresses the bond, it cracks (C). If the crack can be closed, a threaded rod, washers and nuts (D) may be used to keep it together while new wood grows. The new layers of wood eventually cover the hardware and bond the limbs once more. The rod should be inserted 3 to 4 inches above lowest part of crack (E).
If the split limbs are large in diameter, two rods can be inserted in that area three- to four inches above the lowest point of the split. Put these in one rod just above the other, each rod at a 45 degree angle to the split. Seen in x-ray from above they’d look like a cross through the trunk.
If you rely on the tightening of the nuts to bring the limbs together, use double washers. The washer against the wood will be less likely to rotate or wiggle and cause further injury
After everything is in place, if you can cut off the protruding ends of the rod without nicking the bark or pushing against the tree, do that. If you can’t, that’s okay -- it will take the tree more years to cover over those rod ends, but it will still happen.
If your Japanese maple is right up against the house, it will eventually be too big for that area. Learn how to prune it to keep it small. Then if there is damage like this you'll have another option -- cutting just below the split and training a supple, younger limb up and over the stub to become the new top. Read What's Coming Up 188, especially for Afraid to cut a Japanese maple or check out What's Coming Up 176's pruning articles Keep tree small unabridged and Prune dwarf maples.
Whether you brace or prune, it will always be the case that this tree is at risk because it's located so near a roof that may shed snow in a smashing second. It will be a good idea in future autumns to put crutches under the largest branches to help support unusual snow loads during winter.