Grafting is an old and well-established technique by which parts of two separate plants are joined and then grow into one. The lower part, called stock or rootstock, typically provides a hardier or more disease-resistant basis to the plant, or may limit the mature size of the specimen, while the scion, grafted onto the stock, consists of the desired fruit or flower-bearing portion.
Stock and scion must be compatible: unrelated plants cannot be randomly joined together. The closer related species are, the more likely one is successful. Thus, wine grapes can be grafted onto North American grape rootstock, multiple apple varieties onto one apple tree base, desirable tomatoes onto disease-resistant stock, even tomatoes onto their potato relatives.
Collect unfrozen, healthy scions, each 8 to 12" long, during the winter, a few weeks before grafting actually takes place. Store in the fridge, in damp peat moss and enclosed in plastic; soak a few hours before grafting. Then make fresh cuts to trim scions to their desired length; leave at least 4 buds. Don't touch the cut ends, and when grafting, ensure that the original orientation of stock and scion remains the same, that is, that up stays up, and down stays down.
A very sharp blade is used, so that plant tissues are cut, not crushed. For healing to occur, the cambium of the scion, a thin layer of plant tissue found just below the bark or skin of the plant, must be linked to the cambium of the rootstock; it is from this layer that the xylem and phloem, which carry water and nutrients, derive. Thus, the outer tissues of both plants must be lined up before being held into place.
Ordinary tape is as effective as anything else, in terms of holding scion and stock together, until the plant heals. However, enclosing the graft site in plastic may be helpful; it helps prevent the site from drying out. Remove tape once the scion shows signs of growing and the callus at the graft site seems to strain against the tape.
If moving a grafted specimen, make sure that the bud union stays at least 2" above soil level, so that the scion cannot itself grow roots directly into the soil. Should this happen, desired rootstock properties may be lost altogether.
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