Beech (Sylvatica) & Hornbeam (Betulus) Thread Grafting

[0soyoung]

I have never grafted before so I would practice before I would try it on the Beech. Several questions: on a thread graft why is it necessary to drill a hole clear thru the trunk? Why can't one just go 1/2 or 3/4 thru, pick a suitable scion, and cut it off so you have an inter-node with no buds to deal with for an inch or so, drill the hole just a tad bigger than that, and insert scion that still has 2-4 buds on it, wedge up with tooth picks if necessary, seal and wait. I guess I don't understand why it has to go clear through the trunk.

It is analogous to air-layering versus rooting a cutting. An air-layer is supplied water and minerals via the xylem that remains continuous with the mother plant. With a cutting, this xylem connection is also severed and the cutting must survive on its own, so it is a race against time for it to grow roots before it desiccates.

Grafting free scions is analogous to rooting a cutting. You cut it and the receiving tree to expose the cambiums and to put them into contact. The two cambiums produce a callus and eventually a new thin layer of xylem that is continuous across the mating surfaces so that the scion will then be supplied with water and minerals --> it is a race against time for this new common xylem layer to be created before the scion desiccates. As with rooting cuttings, we must do something to maintain humidity around that cutting/free-scion.

There are two ways we can graft while keeping the scion associated with its roots (instead of being 'free' of them): approach or thread. With approach grafting the stems are just pushed up against one another (one approaches the other), Usually makes a groove in the thicker trunk and fits the thinner one into it. As the stems thicken the cambiums will wind up in contact and the graft is formed in time. There is a tendency for the thinner stem to 'pop-out' of the groove, so it is secured in some way, typically with tacks or wide headed nails. Once the graft is completed, the scion's stem to its roots is severed and it is officially a new stem on the receiving tree. Of course, the scion stem could have been a branch of the receiving tree or a previously rooted cutting from the tree, or an entirely separate seedling.

The other way to graft while keeping the scion associated with its roots is to thread the stem through a hole drilled though the bigger stem. The graft eventually forms primarily because of the thickening of the thread. Of course, the thread, being in a hole that is larger, could be free to move around for some time. This is why we 'jam it' by inserting a piece(s) of wood inside the hole. Again, once the graft has completed, we sever the input side of the thread, leaving you with on branch (the output side). Of course, and again, the scion stem could have been a branch of the receiving tree or a previously rooted cutting from the tree or an entirely separate seedling. Thread grafts, however, can only be done with deciduous species, for obvious reasons.

 

[River's Edge]

I am a bit of a latecomer here, but really enjoyed the thread and all the detail. I have the beech pictured here that I just received from Bill V. It is 23" tall and has a 1+" trunk with a great nebari as you can see. It has been suggested by several, that eventually, one or both of the forks at the top need to be removed. When that happens, I will have several nice top branches that could be grafted lower down to fill in gaps. I have never grafted before so I would practice before I would try it on the Beech. Several questions: on a thread graft why is it necessary to drill a hole clear thru the trunk? Why can't one just go 1/2 or 3/4 thru, pick a suitable scion, and cut it off so you have an inter-node with no buds to deal with for an inch or so, drill the hole just a tad bigger than that, and insert scion that still has 2-4 buds on it, wedge up with tooth picks if necessary, seal and wait. I guess I don't understand why it has to go clear through the trunk. I don't want a branch on both sides, opposite of each other, just on the bare side. Thanks for help, Peter

Peter, it would be helpful if you separated the techniques you are thinking about. A thread graft requires the branch pass through the trunk or branch. That is how thread grafting is defined.
If you wish to move a branch, that usually involves a combination of approach graft and peg graft. First an approach graft is attached to the branch you wish to move close to the trunk. The approach graft sustains the branch while the peg graft is healing with the cambium of the trunk. Essential it is a two step technique that begins with developing seedlings or cuttings to use as rooted approach graft material in advance. A more detailed explanation of this approach is contained in the chapter Styling and Maintenance Techniques of Bonsai Maples by Andrea Meriggioli. I have seen many successful examples in nurseries in Japan.
Typically this technique is used to move branches and shorten trunks.

 

[Aiki_Joker]

It may be summer before I update this thread for this year everyone. I am currently away. I look forward to this year's inspection and appraisal though. Strong new buds formed on the branch last season anyway.

 

[River's Edge]

It may be summer before I update this thread for this year everyone. I am currently away. I look forward to this year's inspection and appraisal though. Strong new buds formed on the branch last season anyway.

Thanks for the comment. I have been thinking of the thickening response on the beech. I wonder if the thread graft was placed on more of an angle through the trunk if the response would be altered? This should spread out the thickening response and lessen the visual effect!

 

[Aiki_Joker]

Picture received of the Beech thread graft this year. That is three years to failure.

As the above commenters highlighted, this graft failed to bind to the bottom cambium because it was shimmed to the cambium at the top of the graft. There was too much space at the bottom and my sealant choice did not help things at all.

The other side of the graft however was at an angle such that it could fuse with active cambium on the lower side. This resulted in a reverse thread graft if sorts... Interesting, but a failure nonetheless.

Last year this graft flushed out. But the completion of the fusing on the reverse side last year and the lack of productive tissue on the chosen side obviously resulted in the plant dropping the chosen side last winter.

A good decision. And looking at the relative thickness of the back of this graft, the plant put alot of resources into it in Autumn to ensure that it would survive the winter. Alot of carbs pumped in there indeed. Maybe it was also checking the flow to see if it could get anything through because the caliper increase was greater this year than any other year. The chosen side had alot of light too and the other side was cut back.

Of course complete fusion and development of the relevant vasculature to support the thickness gains are probably the cause of the increased thickening compared to other years... It is just nice to think that the plant is making anthropomorphic checks and trying to please us idiot humans!

 

[Aiki_Joker]

Attached(?)

 

[Paulpash]

Thanks for the update.