From Aggie
Horticulture, Texas A&M AgriLife Extension
Texas A&M
University
System
Cleft Grafting
Cleft grafting is a grafting technique which
allows the union of a
rootstock limb that is much larger in size than the scion piece. Cleft
grafting is conducted in late winter when both the rootstock and the
scion are in a dormant condition.
Common applications for cleft
grafting include changing the variety of an existing orchard
(topworking), adding a branch of an untested scion cultivar to an
existing tree for observation, or repairing a tree that may have had a
branch broken off by storm damage or fruit overloading.
The
limb to be grafted or topworked is cut square with a sharp pruning saw.
The branch is then split in the middle longitudinally using a chisel,
large knife, or a special tool that is a combination blade/wedge
designed specifically for cleft grafting. The limb is split for a
distance of 2 to 4 inches, with care taken to make the split in the
middle of the limb. For species which do not split evenly, the initial
cut may need to be made with a saw to prevent uneven splitting (termed
saw kerf grafting).
After
the split is made, the "cleft" is pryed open and held open with the
wedge end of the grafting tool or another suitable instriment to hold
the cleft open.
A
3 to 4 bud scion stick between 4 and 6 inches in length is then
prepared for grafting into the cleft. The budstick should be obtained
from small limbs or water sprouts that grew vigorously during the past
season of growth (1/4 to 3/8 inch in diameter) as indicated by well
spaced, large plump buds. Very large diameter sprouts and ones which
are small and thin with closely spaced buds should be avoided.
The
lower end of the budstick is trimmed with gradually sloping cuts made
on exactly opposite sides of the stick. The slope of the cuts on the
budstick should match the angle of the cleft as closely as possible.
The
sloping cuts on the budstick should exactly match the shape of the
cleft in the rootstock. Furthermore, the cuts should be even in slope
(not wavy) to allow for maximum contact between the budstick and the
rootstock for the entire length of the budstick. If the budstick is too
blunt, the amount of contact will be too small to promote good healing
of the union.
When the budstick is inserted into the cleft, the
cambia of the two pieces must be matched exactly to promote good
healing. The cambium is recognized as the faint line that separates the
bark from the wood. The bark on the rootstock will likely be much
thicker than the bark on the budstick, so the outer edges of the
budstick and rootstock will not be flush.
The ability to align
the cambia of the two partners to be grafted and maximizing the contact
between the two pieces to promote rapid healing are the two principal
determinants of success in cleft grafting.
The
natural spring in the wood should be sufficient to hold the budsticks
in place. After both budsticks have been inserted and aligned, the
wedge holding the cleft open is carefully removed. The cut ends of the
budsticks, the cut end of the rootstock, and the splits of the cleft
are painted with grafting wax to prevent desiccation of the wood.
The
budsticks should break buds readily during the subsequent spring growth
flush. If both budsticks survive and resume growth, the less vigorous
one should be cut away being careful not to dislodge the other one. A
decision on which one to remove can wait a month or so to see which
grows out most vigorously. However, under no circumstances should both
budsticks be allowed to remain for the entire growing season since
complete healing of the wound will not occur with both in place.
Publication from Aggie Horticulture®
The information, as it is presented on this Website, does not represent
an endorsement
by the State of Texas or any State agency.
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