by Jeff Wasielewski
Grafting is one of the most difficult types of propagation. Propagation by grafting results in offspring that are genetically identical to the parent plant. This is useful for replicating superior cultivars of fruit or flowring trees. Grafting involves joining a piece of a mature tree (scion) to a seedling (rootstock). The scion will become the new trunk and branches of the tree and the rootstock will become the root system. Grafting is generally used with fruit trees that are unable to be propagated using air-layering or cuttings such as mangos. The cambium is a key component in a successful graft as cambium layers from both the scion and the rootstock must be matched for a successful graft. The cambium is an active layer of cells located between the bark and woody portion of a stem or branch.
There are two main types of grafting: veneer and cleft. Both types of grafts require healthy scions (sometimes called budwood) and rootstock. Both the scions and the rootstock should be about the width of a pencil. When selecting scions for veneer or cleft grafts, choose healthy portions of the parent plant that have buds that are going to open soon, but have not opened yet (swollen). The scions should be about 3 to 4 inches long and the width of a pencil and should generally have their leaves removed after they are cut from the parent plant. It may be desirable to leave the top leaves on the scion when completing a cleft graft. Scions should be placed in a sealed bag as soon as they are removed from the parent plant. Scions may be kept several days before they are grafted with good success. With both types of grafting, a high-quality, sharp grafting knife is recommended. A grafting knife differs from a standard knife in that it is beveled on only one side. This unique quality of the grafting knife allows it to be used to make the smooth, flat and even cuts required for a successful graft.
Veneer grafting is done by removing the bark of one side of the scion. The bark is then removed from a portion of the rootstock that is roughly the same length as the scion. A flap of bark should be left on the bottom of the rootstock cut to help the scion hold in place. The bottom of the scion should be cut at a 45 degree angle to fit into the flap left on the rootstock. The exposed cambium (found just below the bark) of the scion and rootstock are then placed together and held in place with transparent grafting tape. The tape should be wrapped from bottom to top firmly, but not overly tight. The tape will seal the graft to retain moisture as well as hold the scion in place. It is important that the cuts made on the both the scion and the rootstock are smooth, flat and equal in width and length. The top of the rootstock should then be trimmed in order to stimulate bud growth in the scion. Once the cambiums have been joined, they will grow together and form a strong union of scion and rootstock which will makeup the newly propagated plant.
Cleft grafting is done by cutting of the top of the rootstock and gently making a cut down the middle of the rootstock about ½" in depth. The scion is then prepared by creating a thin wedge at the base of the scion which will fit into the cut made in the rootstock. The scion is then placed into the rootstock. Both rootstock and scion should be the same size and there should not be any air space when the two are joined. Scion and rootstock are then held in place by grafting tape. It is not necessary to wrap the entire rootstock. Only the union needs to be wrapped. The cambium layer for both rootstock and scion will begin to grow and cause a union which will form the newly propagated plant.
Aftercare for both types of graft is similar. After the graft is completed, the graft should be placed in a shady, humid, protected area. The graft union should be complete in approximately 4-7 weeks. Both types of grafts will begin to grow leaves from the scion when the graft is successful. It may be necessary to cut holes in the grafting tape to allow the leaves to emerge. The grafting tape can be completely removed once a strong union has been formed. With a veneer graft, the top of the rootstock should be removed down to the scion once the tape is removed. Newly grafted plants are ready for planting when they have grown approximately 14" in length.