Approach Grafting for Bonsai

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Advantages and Disadvantages of Approach Grafting over Thread Grafting

One of the principle advantages of approach grafting is that the foliage does not need to be removed from the scion in order to carry out the graft. This makes it suitable for coniferous species such as Pine/Pinus and Juniper/Juniperus.

Approach grafts are also easier to apply in situations where the wood to which the scion is to be attached is thick in diameter, making drilling a hole difficult or impossible. And because the trunk does not have to be drilled, unlike with threadgrafts, several approach grafts can be applied close together.

Four field maple seedlings approached-grafted to the back of a much larger field maple bonsai

Four field maple seedlings approached-grafted to the back of a much larger field maple bonsai

The trunk of the field maple above is approximately 4” in diameter. Four field maple seedlings have been attached to the back of this trunk to create new surface roots and an improved nebari; this would not be as easy to carry out with 4 threadgrafts in such a confined area. Using approach grafts in the above situation also means that the thick trunk does not have to be repeatedly drilled nor will the trunk have 4 threadgraft-exit scars being created in full view of the front of the tree.

There are of course, disadvantages with approach grafts that must be taken into consideration. Firstly, approach grafts are not as ‘clean’ as threadgrafts. Rather than the simple entry and exit hole of the threadgraft, an approach graft requires that a strip of bark be removed in order that the scion is attached. Even after the graft has taken and the area has calloused and healed over, the scar can on occasions look unnatural and therefore be visible. Whereas when a threadgraft is severed, there is only a small entry hole to callus over, the strip of damage to the bark can take longer to heal.

Successful approach grafts are also more reliant on the tree species having a thick bark/cambium layer and strong callusing/healing characteristics. Approach grafting is less suitable for tree species with thin bark, slow healing/callus formation characteristics and in particular, a susceptibility to the cambium layer dying back around the edges of wounds.

Finally, if all goes wrong and the graft does not take, a threadgraft at worst will leave you with two small holes/round uro in the trunk whereas a failed approach graft can leave a nasty and visible scar.

In summary, while approach grafts can be used to great effect and are fairly straightforward to carry out, it much harder to know when and where to utilise them. Great consideration has to be given to the tree species to be used, the position of the graft, the visibility of any resulting scar tissue and the health and vigour of tree in question. It is important that both the scion and tree to be grafted are growing strongly to maximise callusing, healing and minimise the time taken for the graft to take and for any resulting scars to heal over.

As a general guide, I would suggest considering approach grafts for all Acer/Maple species (red leaved varieties are much less suitable due to reduced vigour), Ulmus/Elms, Ficus/Figs, Pinus/Pines and other similar coniferous species with thick cambium/bark such as Picea/Spruce, Cedar/Cedrus, Larix/Larch and Chamaecyparis/Cypresses.

To gain experience with approach grafting, Trident, Mountain maples or Ficus species are by far the best subjects to start with due to their superior growth rates and callusing/healing abilities. I would also suggest practicing on ‘potentsai’, that is, developing trees being grown in training pots that are exhibiting vigorous growth rather than slower growing specimens in bonsai pots.

The Process of Applying an Approach Graft to an Acer Palmatum (Japanese Maple) Bonsai to Produce a New Branch

The subject of these images is an Acer Palmatum or Mountain Maple Bonsai with a thick trunk that has a ‘blank spot’ where a branch is needed but no new shoots or buds have previously appeared. A second purpose of this particular graft is that the new branch will speed cicatrisation of the existing large wound that resulted from the removal of a large branch 2 years previously.

Acer Palmatum or Mountain Maple Bonsai

The first part of this process is to mark exactly the point where it is intended for the new branch to 'emerge' from the trunk when the graft has finally healed over. In this case I have used a black marker pen.

cambium layer and bark is cut away

With a very sharp knife, the cambium layer and bark is cut away along the intended path of the graft. Try to take care to make a channel just large enough to accept the scion without damaging the bark of the scion itself.

deep enough for the entire scion

The wood within the channel is then removed; I have used a Dremel in this case but hand tools are more than adequate for the job. It is important that the channel is deep enough for the entire scion to be seated at or just below the level of the trunk, where possible. This will eventually produce a cleaner scar and make the initial fixing of the scion easier.

scion or 'donor' shoot from the same tree

I am using a scion or 'donor' shoot from the same tree. This is a shoot from a different part of the tree that has been allowed to grow long enough to be bent into the grafting position.

A branch from a separate tree can be used, however bear in mind the practicalities of keeping a separate tree in position while the graft is taking. The scion must be of the same genus as the tree to which it is to be grafted; it is normal that the same species and/or variety is used to ensure that the bark and foliage of both scion and grafted tree are the same. However, it is not unusual for the foliage of one Pine or Juniper species to be grafted to another

It is paramount to the whole process of approach grafting that the scion will be fixed very firmly into position.

Secure fixing of the scion ensures that the graft does not move around and break while healing. It also ensures that the scion cannot be 'rejected' or pushed away by the cicatrisation/callusing of the trunk. Be wary that even after the graft has fully taken, it will be some years before the scion is held strongly in place by the new scar tissue. Securing the scion manually now will save the accidental break of the graft in future years.

securing the scion

There are a variety of methods for securing the scion. Avoid using steel but copper, brass or aluminum are suitable. I like to use ordinary aluminum or copper bonsai wire. However tacks, pins or screws can also be used. Circled above are two 1.5mm pilot holes I have drilled so I can insert a staple made from 1.5mm aluminum bonsai wire.

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