by George Buehler

Have you ever needed a branch on a tree? Have you bent an existing branch around in order to hide a spot on the trunk that needed a branch? Do you want to try something different to help the overall design of your tree? Do you need another nebari to balance the root profile? If you answered yes to any of the above, you might want to consider thread grafting. This technique only works for deciduous and broadleaf trees.

Thread grafting involves using a branch from the subject tree (or in some cases, another one that will have to be kept in close proximity throughout the process) and basically 'threading' it through the trunk. You accomplish this by drilling a hole through the trunk and 'threading' a branch through the hole in the trunk. This may sound scary but is really quite simple as long as you follow some basic guidelines. The buds on the tree and most importantly the branch you will thread must not be swollen, although I have seen one master perform this technique on a partially leafed out trident maple – he simply stripped the branch he was threading and proceeded. Another expert advises to cut off the leaves rather than strip the branch to avoid damaging the axilary buds.

• You want the branch to be as close as possible in diameter to the hole you are about to drill.
• Make sure the branch (in most cases, really a leader) is long enough and supple enough to be useful. You may need to let several shoots grow freely the previous growing season to get a useable shoot.
• You want to do the grafting when growth of the scion is most vigorous.
• Practice patience!!

Beginners take heed. This technique has a very high level of success. It is not difficult; and I realize some may consider boring a hole into a trunk as dangerous, but it really isn't. Remember, the "living area" of a trunk is very small; the "heartwood" is basically support material.

Remember the key to this technique is to be patient! Normally the 'graft' takes in one season, but waiting two seasons is not a bad idea. The sign to look for is when the "exit" side of the branch (this is the side where you want the new branch) swells to a diameter greater than that where it ENTERS the trunk. When this is very obvious, you can consider severing the branch at the point of entry into the trunk. If the graft was successful, it will not suffer any setback. If not, it will die quickly.

Now let's look at the procedure. You need to determine where you want the new branch to be. I like to use a piece of masking tape, and wrap it around the trunk at the location just above where I want the branch. I then draw a line on the masking tape at the angle I want the branch. Most references I have seen indicate that the hole you will drill should be almost horizontal or "slightly" going uphill. If the shoot faces slightly upwards, the side to be the new branch (at the exit side of the hole) will bud out and grow more strongly than the entry side. BEFORE you drill the hole, check once again that the branch you intend to use will bend enough to go through the proposed location. Select a drill size that is very slightly larger than the size of the branch you will use. You might want to start with a small drill and gradually work up to the size of the hole needed. Now take a deep breath, center the drill bit on the trunk, and drill the hole. Do not push extremely hard, especially as you get close to exiting the trunk, let the drill bit do the work. You don't want to break the bark as the drill exits the far side of the trunk. Although this won't hurt the tree, it will be unsightly. Run the branch through the hole. Particularly with soft-wooded shoots, try to pull the shoot through rather than push it, if possible. To ensure the new grafted branch will have a short first internode, position the graft so a bud (node) is a short distance from the exit hole. Leaving a long distance to the first bud will mean that in the future, the first secondary branch will be a long way from the trunk. If the drilled hole is larger than needed, you can take a piece of thin wood from elsewhere on the same tree and gently insert it into the hole to fix the position of the scion since this will help the union to take quicker.

Now seal both openings where the branch enters/exits the trunk. Almost any wound sealer can be used as long as it is fairly stiff. Lac balsam is a good choice. The one caveat is to only "seal" the opening; do NOT force the sealant INTO the hole. The success of the graft depends on the union of the branch (scion) with the cambium of the trunk. Excess sealant may prohibit this.

Encourage strong growth of the threaded scion. Feed the tree well to ensure strong growth. Remove any new growth on the entry side of the thread graft to encourage maximum growth on the exit side. Do not prune the thread graft as this will slow thickening.

When it is time to cut the mother branch, do not detach all of the redundant side of the graft at once (since the scion will still receive a little energy and be supported from the entry side of the branch). Detach the scion from the parent branch, but leave a length of the donor branch in position so that the scion can slowly become accustomed to being entirely supported by its new parent trunk. Over the course of three or four weeks, the donor scion should slowly be shortened. The entry hole can then be pruned flush to the trunk and allowed to completely heal.

Wiring should not be attempted until the mother branch is severed and then with extreme caution. If it is absolutely necessary to start shaping the new branch before the donor branch has been cut, extreme caution should be exercised and no drastic bends should be attempted.

THREAD GRAFTING NEW ROOTS

The principle of thread grafting new roots is precisely the same as for branches, except that when the graft has taken, you retain the "parent" part and discard the other. The best time for this operation is in early spring, before the buds open; but it can be done with care any time during spring/early summer.

Find a healthy seedling of the same variety as the main tree. The stem of the seedling must be roughly the same thickness as the existing nebari on the main tree.

Drill the hole at an angle sloping upward from the exact point where you require the new root. Start drilling the hole from the opposite side to where you need the new root.

Excavate a wedge of soil where you want the new root, to accommodate the roots of the seedling.

Prune all lateral branches and leaves off the seedling and push it up through the hole, making as tight a fit as possible. Once again, seal the entry/exit hole, but don't push the sealant into the hole.

Gently arrange the roots in the excavated space and refill with soil. Water thoroughly and keep the assembly in the shade for a few weeks.

Feed the tree well to encourage rapid thickening of the inserted stem and healing of the wound.

Always wait a season longer than you think is necessary before cutting off the free-growing top of the inserted stem, leaving the trunk base and roots behind.