(Readers who receive the Fort Wayne Bonsai Club newsletter will see this in the current issue in slightly different form.)
During the Exhibit Critique at the 2016 Mid-America show, Colin Lewis described a grafting technique that gets around one of the common difficulties encountered in grafting. That difficulty is making sure that the cambium of the scion and the cambium of the stock line up with each other at all (or almost all) points. Until your eye has been trained by some experience, making sure that the cambium layers line up all around can be a very frustrating affair.
The technique Lewis shared abandons any attempt to make the cambium line up all around in exchange for eight guaranteed points of cambium-to-cambium contact. Let me try to explain the method, using some twigs cut from the ash tree in our front yard for the purpose. (In case anyone wonders, the intent of this post is to explain and illustrate the concept, not record an actual graft.)
Step 1. The first step is to trim the scion flat on one side. The cut needs to be as smooth as possible. Then turn the scion over and trim the opposite side in the same way. The surfaces of the trimmed areas need to be as close to parallel as possible.
|The green arrows point to the cambium, the thin green layer between the brown of the bark and the off-white of the sapwood.|
The chartreuse arrow points to the foliage end of the scion.
This technique, by the way, can be used equally well when a seedling or rooted cutting is being grafted in and its own roots are being retained until the graft takes. You just trim down into the sapwood on opposite sides, as illustrated, at the point on the scion where you want it to contact the stock. Make the trimmed-down area just slightly wider than the flap bed (the exposed area of cambium and sapwood on the stock; see picture 2.)
Step 2. Cut the flap in the stock.
|Again, the green arrows point to the cambium, the chartreuse toward the foliage.|
Step 3. If the scion is thin enough after trimming, you can skip step 3. But if the scion is thick enough that you won’t be able to close the flap properly, you need a notch, no wider than the scion and just deep enough that the upper surface of the scion lies flush, or nearly flush, with the top of the notch. Note the red arrow! If I had actually been making a graft, rather than simply trying to illustrate a technique, I would not have left the floor of the notch so rough. For an actual graft, it needs to be smooth and flat.
|Do not leave the floor of the notch rough like this.|
By the way, you can make the notch at any angle you choose, depending on the angle of growth you want the new branch to take. Handy, huh?
Step 4. When you lay the scion in the notch, the line of cambium on each side is going to cross each of the lines of cambium in the stock. That gives you four firm points of cambium-to-cambium contact, two on each side of the scion on its underside.
|Each of the green circles sits above a point of cambium-to-cambium contact on the underside of the scion.|
Step 5. The underside of the flap also has two longitudinal lines of cambium, and when you close the flap, each of them is going to come into contact with each of the two cambium lines on the upper side of the scion. This gives you four more points of cambium-to-cambium contact.
You now have four cambium-to-cambium points of contact on the underside of the scion, and four on the upper side, for a total of eight. This is enough for a good join.
|Again, each green circle sits above a cambium-to-cambium contact point on the upper side of the scion,|
as well as one on the underside.
It's important that the flap lie flat or nearly so, so that cambium-to-cambium contact can be re-established between the flap and its bed. Otherwise, you risk some dieback and an unsightly wound.
(Don't forget that when you make an actual graft, there are other things to consider as well: a very sharp knife and good aftercare, to name just two.)
Lewis pointed out another benefit of this technique: Sometimes the stock branch is intended to be cut off after the graft takes, and the scion is intended to take over. In that event, you’ve introduced some movement into the eventual finished branch in the process of making your graft!
:-) :-) :-)