How to make a cleft graft
Now that I've cut
the top off of my young tree, I can insert the
scionwood. Step one is to slit the trunk of the tree vertically
for about two inches --- making the cleft.
Orchadists have special
tools for cleft grafting, but I figured I could find everything I
needed between the kitchen and the toolbox. The small, sharp
knife shown below was too miniscule to do the job, but a big, dull
butcher knife combined with a hammer was just right.
I hammered the big knife
into the center of the trunk, then pounded on the sides of the knife to
insert it a bit deeper. On my second tree, I didn't make the slit
quite so deep, and found it more difficult to insert the scionwood, so
be sure to make your slit big enough the first time.
The next step is to
widen the cleft using a wedge. Again, professionals use a special
tool for this procedure, but a screwdriver pounded in easily and worked
the scionwood as described previously, then insert two pieces, one
each side of the wedge. If the cleft isn't quite as open as you'd
like, you can rotate the screwdriver slightly to widen the gap.
Scionwood insertion is
the trickiest and most important part of the whole process, so take a
few minutes to make sure you're doing it right. The diagram below
shows a cross section through a piece of scionwood, illustrating the
layers of different kinds of cells that make up a twig.
You can think of the cambium
as the stem cells of the plant world --- the cambium cells are still
physiologically flexible and can grow together with the cambium of a
different tree. The cambium is relatively easy to see if you have
good eyes since it tends to be bright green. Your goal is to make
sure the cambium of your scionwood lines up with the cambium of the
tree you're grafting onto.
Your gut reaction will
probably be to try to make the scionwood fit flush against the side of
the tree being grafted onto, but that's not quite right. As a
tree grows, it not only expands the xylem (the woody part in the
center), but also the phloem (which turns into the bark). So, the
cambium is going to be a little deeper into the
older tree being grafted onto than it is on the little twig of
scionwood. That's why most people recommend making sure your
scionwood is slightly indented as you look at your graft from the side.
One way to hedge your
bets is to insert your scionwood at a slight angle, as is shown in the
drawing to above, so that the cambial layers intersect somewhere. This type of angled
scionwood placement won't give you as strong a connection, but is
better than nothing if you're not sure you'll get your cambial layers
lined up otherwise.
One last note on
scionwood placement (which you really should have considered when
making your cuts) --- most sources recommend that the first bud on your
scionwood sits just above the top of the tree being grafted onto.
If you had extra scionwood length, now is a good time to cut each one
down to two or three buds. Stay tuned for tomorrow's post, in
which I'll explain how to seal the cut surfaces.
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