Threadgrafts are by far the easiest and most reliable grafts available
to the bonsai enthusiast. Normally used to create new branches
on a bonsai, a young, pliable shoot is threaded through the trunk
of the tree.
As
the shoot grows and fattens, the cambium layers of the shoot and
the trunk are forced together and a join or graft is made.
Threadgrafts
can also be used to attach new roots to a bonsai. With the English
Hawthorn (Crataegus monogyna) below, a new root is required to
improve the nebari (rootspread) of the tree and this is provided
by thread grafting a young Hawthorn seedling.
For
more details on the subject of threadgrafting, please visit:'Threadgrafting
Bonsai'
A
second useful and related article is ‘Approach
Grafting New Roots’; both threadgrafting and approach
grafting new roots are equally viable techniques and should be
seen as techniques that can be used individually or in conjunction
with each other.
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The roots of
the Hawthorn immediately after collection. As is fairly typical
of this species with its deep-growing tap roots, there were few
fine roots in the rootball that I collected.
Pictured here
is the rootball at the time of collection. The tree was planted
into an inorganic soil mix with a little added sphagnum moss. |
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3 years later,
the same rootball is pictured after rootpruning.
The nebari
and rootspread is developing well though the lateral surface roots
are very straight and untapered; this will be improved over the
years by selective pruning to increase ramification of these roots.
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When the tree
is repotted it becomes obvious that the areas either side of one
of the old thick taproots is ugly and bare.
There are a
number of ways of introducing new surface roots; some owe much to
luck. Threadgrafting a new root is a relatively quick and sure-fire
way to improve the nebari. |
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The seedling
used for a threadgraft must be of the same genus as the parent
tree but it is also preferable that it is of the same species.
Different species (such as Acer campestre (the field maple) and
Acer palmatum (Japanese maple) will graft together but the bark
colours and rate of growth are ill-matched. This will cause the
graft to look artificial in future years.
It is important
that threadgrafting is carried out before the seedling starts
to bud out in the Spring as at this time the leaf buds swell and
are easily dislodged as the seedling is threaded.
The seedling
is bare-rooted and any side branches are removed.
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A hole is drilled
through the trunk of the bonsai.
Though it is
preferable that the hole for the threadgraft is made from the entry
side to ensure it's position with absolute accuracy, this tends
to be difficult if the tree is already potted up.
Try to make
the exit hole for the graft in a position where it will be hidden
from view (facing the back of the tree).
Use a wood drill
bit that is slightly larger than the diameter of the seedling so
the seedling can be introduced through the hole without damage.
However, making the hole too big will increase the time needed for
the graft to take. |
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If a large
diameter drill bit is needed for the seedling to fit, use thinner
bits to make an initial pilot hole and gradually widen the hole
with larger bits until the correct diameter is reached.
Ensure that
the drill bit is fixed very firmly in the chuck; wet wood has
a lot of 'drag' and there is potential for the drill bit to come
out of the drill and become stuck inside the trunk.
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After drilling,
the seedling is threaded through the hole.... |
.............until
it is finally in position.
As can be
seen in this picture, the seedling has been selected for matching
bark colour and the way the taproot naturally bifurcates (splits
into two) creating a more natural surface root.
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The roots of
the seedling are covered with soil and the holes in the main trunk
sealed with cut paste to encourage rapid healing. |
The seedling
will be encouraged to grow strongly this year; the greater its
growth, the faster the graft will take.
When the seedling
and the main tree have visibly joined and healed together, the
upper part of the seedling will be gradually pruned down until
all that is left are its roots growing into the main tree.
Patience is
necessary; at the very earliest this separation will take place
in a year's time.
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The
main tree and the threadgraft July 2005 |
Update:
December 2006. By August of this year, the threadgrafted shoot
had grafted tightly into position. The top section of the threadgrafted
seedling was pruned away leaving its base as part of the main
tree.
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The Hawthorn bonsai
itself; December 2006
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Here is
another example of threadgrafting roots; this time on an Acer
campestre/Field Maple.
Acer campestre,
as with most Acer species, exhibit strong root growth. Though
there are three strong lateral/surface roots that are being
to develop some division and taper; there are also two large
gaps in between these three surface roots.
With many
maples, new roots could be encouraged by simply scoring the
bark of the trunk, however, if new roots were to emerge,
they would require many years of strong growth to thicken
as much as the three existing surface roots.
Instead,
three young, pencil-thick Acer campestre saplings are thread-grafted
into the gaps in the nebari. These will take much less time
to become nearly as thick as the existing surface roots.
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In
this image the three saplings (new roots) have been threadgrafted
into position.
A
couple of reed-sticks have been lodged across the
roots to ensure the new roots keep their positions when
they are covered back over with soil.
Notice
that the exisiting larger roots have been pruned to ensure
a smooth transition into the smaller secondary surface roots;
just as you would ensure a smooth transition between the
branch sections of a bonsai.
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