Top working is a type of graft that involves removing the top portion of a tree and replacing it with a scion, a specially prepared branch, from another tree. This technique allows a hardier, more disease-resistant tree to be joined to another tree with more desirable fruiting traits. While there are several methods of top working trees, the four flap method is an effective way to top work pecans. It is relatively easy to perform and results in a heavier, more substantial graft on more mature pecan trees than other top working techniques.
Gather mature branches from the tree to be grafted in early spring, prior to buds opening. The branches should be about 1 inch in diameter and have buds on them. Cut the collected branches into 10-inch lengths. Place the cut lengths in an airtight container and store them in a refrigerator.
Prepare a scion from the stored wood when buds on root stock trees begin to open. Select a piece of branch wood that is the same diameter of the root stock tree to be used. Trim the wood to about 6 inches long, with two or three buds on it. Starting about 2 inches from the trunk end of the scion, cut the bark away on four sides.
Select a pecan sapling that will act as the root stock for the graft. Cut the trunk of the sapling straight across with a pair of pruning shears. Place a snug rubber band on the trunk about 4 inches from the cut. Trim back any remaining branches on the sapling to around 6 inches long.
Make four evenly spaced vertical cuts through the bark of the root stock tree from the cross cut to about 2 inches down the trunk. Carefully peel the bark to form four flaps. Cut off the remaining center wood where the flaps end.
Place the cut end of the scion into the center of the bark flaps on the root stock tree, aligning the cuts in the scion to the flaps. Fold the flaps up around the scion and slide the rubber band up to hold them in place.
Wrap the entire graft with grafting tape. Crumple a piece of aluminum foil around the graft to protect it. Slide a plastic bag with one corner cut out onto the scion until it covers the graft, and tape it in place above and below the foil to seal the graft.
Check the graft occasionally to see if it has taken. If so, the buds on the scion will begin to open and sprout leaves. Remove the plastic bag, foil and tape once the graft has completely healed. This usually takes around six to eight weeks.
Control the growth of the graft. Remove the growing tips of branches that form on the graft if they are growing too quickly. This will help to form a stronger trunk. If the graft is growing too slowly, remove some of the lateral branches from the root stock. After two or three years, when the tree is well-established, remove any remaining lateral growth from the root stock.