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.|