Theory of Bark Grafting

[jcaldeira]

I need help understanding the theory of bark grafting.  When bark is peeled away from a stem/stock, which layers are on the bark, and which remain on the stock?  Does peeling a bark tear the vascular cambium layer in half, or is it on one side?  Is the graft joining only on the stock side, or the bark side?




I recently made three bark grafts to top-work a citrus tree, and only one succeeded.  That's enough, as it's quite healthy, but I don't really understand how bark grafts work.  Specifically where is the scion and stock joining together?



Thanks!
John

[Guanabanus]

Good questions--- I wish I knew the answers.   Chances are it varies a lot among types of plants, and that it varies due
whether the bark is "slipping or not.

[shaneatwell]

Once looked for the answer to this myself without success.

As far as I can tell, most grafting has to do with proximity, not actual contact of the right tissue types. Cutting induces an injury response. The rootstock (and scion?) sends out cells to repair the damage and if its close enough and protected enough, finds the partner tissue in the scion. Then starts building (or converting to) the appropriate bridging tissues. I think this is why grafts that don't really make sense probably work.

[fyliu]

It's the base of the scion and the wood side of the rootstock. You cut the scion at an angle and keep it flush to the wood of the rootstock after you peeled the bark.

Some people will cut a little off the other side of the scion so there will be some contact with the bark of the rootstock. A couple of cells is all it takes to connect. Left undisturbed they will divide and form a stronger connection.

[socal10b]

Citrus is the easiest plant to graft for me so far. I'm 100% sucess on top worked trees. I made T-cuts on rootstocks and then prepare scions with 2-3 buds make a 2inches long v-shape cut ( like u would when u r cleft grating) insert scion into the T-cut. You need to secure the T-cut really tight. Cover it with a plastic bag to prevent rains get in. Within 2 weeks u should see growth. I guess I made good connections with cambium with 100% success rate?

[jcaldeira]

It's the base of the scion and the wood side of the rootstock. You cut the scion at an angle and keep it flush to the wood of the rootstock after you peeled the bark.

Some people will cut a little off the other side of the scion so there will be some contact with the bark of the rootstock. A couple of cells is all it takes to connect. Left undisturbed they will divide and form a stronger connection.

Thanks, Fyliu.  That's the kind of info I'm looking for.  If it's only the wood side of the rootstock that joins, it seems the best scion cut for a bark graft would be a single diagonal cut; not a dual cut as in a cleft graft.

Your thinking is somewhat supported by the success of patch buds, where a piece of rootstock bark is removed and replaced by a piece of scion bark containing a bud.  In this case, though, the rootstock is seemingly not joining to the same layer on the scion, but the layer that's attached to the bark.

I'm tempted to do a few more bark grafts on a throw-away tree and then dissect the successful grafts to confirm what's really happening.

[jcaldeira]

I found this relevant text in the book "The Propagation of Tropical Fruit Trees" by R.J. Garner, S.A. Chaudri, et.al., 1976:

"Any grafting process which involves lifting the rind from the wood when the cambium is in active growth will reveal the position of the cambium, for it is in this region that the separation occurs.  Some cambial tissue adheres to the lifted rind, whilst some remains attached to the wood, and much of it is moist and slippery to the touch.  This cambium, whether remaining on the wood along with the other meristematic elements, or on the rind, is able to continue growth, laying down new rind on the outside and new wood on the inside, provided it is protected from the air and does not become infected with destructive organisms."  (page 85)

[shaneatwell]

Nice!