Approach Grafting Roots for Better Bonsai Nebari

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Timing: Speed of Callousing vs Health of the Seedling when making Approach Grafted Roots

When approach grafting young seedlings to the base of a bonsai, there is something of a quandary. Is it better to make the graft in the Spring/during dormancy when it is safer to disturb the roots of the seedling but wound healing or callusing of the bonsai is poor or non-existent? Or, do you make the graft during the Summer when the graft will take more quickly though it means exposing and disturbing the roots of the scion while it is in leaf?

As discussed previously, I believe it is a case of weighing up the risks of both dieback of the channel edges and the possibility of poor or slow grafting or the risk of exposing the roots of the seedling during the growing season.
Roots can be and are often approach grafted to many species in early Spring but I would thoroughly recommend summer grafting for those species with poor callusing characteristics or species with a tendency to dieback around the edges of wounds.
In general, I prefer to carry out all approach grafts during the Summer. To minimise any risks to the scions, I ensure that they are root pruned as appropriate during the preceeding Spring and planted individually into small seed-pots so that the scion can be lifted from its container and planted (and grafted) to the main tree with minimum disturbance.

Separating the Newly Grafted Root

As described previously in the article ‘Approach Grafting’, the exit or 'top' of the scion will become noticeably thicker than the entry or 'bottom' of the scion. This allows one to determine that the scion has grafted to the trunk.

Obviously, in this case, it is the base of the scion that is kept and so the exit or 'top' of the scion is removed and dressed almost as though it is simply a low branch being removed.

In the case of newly approach-grafted roots on deciduous and broadleaf species, I find that there is a tendency for the scion to produce new buds and shoots for anything up to 2 years after grafting. These should be removed as and when they appear.

Failure of an Approach Graft

Approach grafted roots cannot really fail and die; they simply take a very long time to graft to the main or host trunk. However, there are several reasons why an approach graft can be very slow to graft to the main trunk.

Firstly, it is of great importance to recognise that strong callusing of the main trunk is necessary for the cambium layers of the scion and main trunk to be forced together in order that they can graft. Strong callousing is produced by fast growing, healthy and vigorous trees and tree species.

A sick, weak or slow-growing rootbound bonsai will not callous strongly enough to graft very quickly. Equally, the scion must be healthy, well-fed and allowed to grow freely in order that it thickens enough for its cambium layer to be forced against the cambium layer of the main tree.

Lastly, patience is essential. Successful approach grafts are not a quick process.

Further Examples of Approach Grafting

As with approach grafting new branches, grafting new roots is not a difficult technique to carry out. However, it is much harder to know in which situation approach grafting is suitable or appropriate. Much depends on individual tree species, individual specimens and the best timing for the given sitiuation.

Here are two further examples of approach grafting roots;

Field Maple (Acer campestre) root-over-rock

Field Maple (Acer campestre) root-over-rock

This Field Maple (Acer campestre) root-over-rock has a poor spread of roots (top image). To improve the appearance of the roots, a young field maple seedling is approach grafted (on the left) and a second seedling (on the right) is threadgrafted. Both of these grafts were carried out at midsummer.

UPDATE July 2008

field maple bonsai roots

The two grafts made during the summer of 2007 (shown above) have healed well; additionally another dozen new grafts have been made to further develop the root spread.

 

Acer campestre bonsai

The above image shows the back of a second Acer campestre bonsai with its surface roots uncovered during repotting. Though there are roots at the back of this trunk, they are too low and new roots are needed in the middle of the area circled in red.

Previous attempts to prompt new roots have included a wire tourniquet (just visible below the circled area) and drilling holes in the trunk (these are filled with rooting hormone and can sometimes prompt new root growth around the wounds. In this case it just prompted a sucker above one of the three holes).

Acer campestre bonsai

This second image shows the same trunk 2 years later after 4 saplings have just been approach-grafted. The second root from the left is a successful approach graft taken just 12 months previously.

The root to its right has just been grafted but not yet sealed. In this image it is possible to see the tiny brass screw holding the sapling in place.

For a more detailed article covering the root development of this bonsai please see
Grafting a Better Nebari onto a Acer campestre/Field Maple

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