Whenever the opportunity presented itself at a festival, convention or other event I have asked fellow bonsai enthusiasts if they were successfully able to graft on Hackberry (Celtis sinensis). The answer was always in the negative.
I believe that being able to graft is an invaluable skill for any bonsai artist to master or at least be capable in. The styling opportunities it presents are really useful. Sometimes in the design of your tree a branch in a particular position would make such a big difference to the positive and negative spaces or would simply fill a gap in your canopy. However, I find that hoping and praying that a bud will form into a branch in that precise position, especially on a reasonably old tree, is really a gamble which you are most likely to lose.
I regularly graft onto common deciduous species such as acer and ulmus (Read more about this here) but all my efforts with celtis have been in vain. Without anyone locally that has met with success I determined to look internationally for help.
When the chance to visit Taiwan at the end of 2017 for the BCI convention came up, I immediately began looking for a Taiwanese master who would be willing to teach me more about how they create such fantastic Celtis, and of course how to successfully graft with this species.
I am about to show you the two methods which were demonstrated to me and I trust they will inspire you to try it at home.
The Taiwanese bonsai artist featured in this video clip is Master Chang Yong Zhou.
This method is essentially an approach graft, which I had tried many times before. However, on further contemplation it has occurred to me that where I went wrong was that I was trying to graft a tree which was in a relatively confined container and thus possibly not growing as vigorously as it would need to in order for the graft to be successful.
Celtis, whatever the species is which we have here in South Africa, is a slow healer. When you see this, you should expect it not to graft easily either. In contrast the species I mentioned before heal quickly and easily, thus they will also graft easily as the cambium has the ability to fuse rapidly (the reason they are also able to callous quickly).
Although I have not personally tried this method, as I have been focusing on getting the trees I wish to graft on super healthy, I would suggest the following as two requirements for this graft to be successful on Hackberry bonsai:
Your trees must be growing strongly, most likely planted in a wooden box (learn how to build one here) or some oversize container as this species is a gross feeder and drinker. Better still this graft should be done while the tree is still being field grown.
The graft should be done at the peak of sap flow. This will be just as spring leaves become leather hard.
To perform the graft you will need the following tools:
Sharp grafting knife
Parafilm grafting tape
Sealant (in the video sealant is not used however I would encourage you to do so. The climate in Taiwan is tropical and thus very humid which in my mind is a game changer)
Decide where you want to graft.
Identify the branch which you are going to use to graft with, which I will from now on refer to as the scion. It will need to be hardwood, not softwood from this season’s growth. It should be flexible enough to be bent around to the position of the graft without snapping. There should be a fork in the branch.
Remove the bark and some of the wood of the scion using your grafting knife on both sides of the scion.
Carefully saw the trunk and then widen the cut using a grafting knife until the scion fits TIGHTLY.
Secure the scion in place with parafilm which will eventually perish of its own. Alternatively, you can use Plastrip grafting tape too, which also does not stretch as much.
Seal any gaps or openings with sealant.
Further secure the scion using wire. If the scion has any movement it will not fuse.
After a few months have passed confirm the graft has taken by checking the girth of the scion where it enters the trunk and where it exits. If the graft was successful, the girth at exit will be noticeably thicker.
Begin reducing the sapflow to the scion by cutting the whip on the entry side of the graft, so the graft strengthens its sap flow to the trunk.
After a few more months check if the graft is still doing well and if so, you can sever the whip entirely.
Final comments on method #1
You will notice the fork in the branch being grafted onto the trunk. Although I am not 100% certain as language was a bit of a barrier between master and student despite the best efforts of an interpreter. I believe the fork serves two purposes; firstly to increase the sap flow and also present a branch which can be used in the future design of the tree which emerges from the trunk at a more natural angle i.e. not out of the side.