Grafting is used to reproduce a pear or apple tree's original variety (cultivar). Seed from the fruit does not reproduce the cultivar because it has usually been grafted onto a strong rootstock of another cultivar. Topworking is the term used to describe cutting back the branches of an established tree to graft another cultivar onto it. Grafting a single bud into an existing tree is called budding onto understock. July to August is the optimal time to graft because buds are beginning to open. Trees under 5 years old are best for topworking and bud grafting.
Cut a bud stick from the new cultivar's present year growth. Choose a slightly brownish mature bud on a branch ¼ to ½ inch in diameter. Cut off the leaves and the tip end. Wrap the bud stick in wet burlap, moss or paper to prevent drying out.
Make a T-shaped cut 15 inches from the understock tree trunk on a side branch. Carefully open the flap edges of the cut with a sharp knife to loosen the bark.
Cut a bud from the bud stick that includes a thin piece of attached wood. Insert the bud into the T-shaped cut, with the bud facing outward from the tree trunk.
Tie the bud graft onto the tree branch with adhesive tape or electrician's tape. Wrap tightly but do not cover the bud.
Remove the tape in two to three weeks, cutting from the side opposite the bud. The bud graft will remain dormant until the following spring. Cut off the branch above the bud as soon as it begins to grow.
Remove all extra growth after the second year, keeping only the bud-grafted tree shoots. Do not allow shoots to develop from the original rootstock cultivar after you have grafted on a new bud.
"Hibernal, Columbia, or Virginia crab, because of their vigour and their strong, well-placed branches, are very good understocks," according the University of Minnesota Extension website information on grafting. Other grafting methods include the whip graft, cleft graft and the side graft.
Grafts may fail if the understock cultivar is unhealthy or the new cultivar is infected with harmful insects such as aphids.