Two common methods of propagating grape vines are by cuttings and by grafting. Cuttings root and grow as a single variety, perpetuating any weaknesses of the parent vine in the cuttings. Grafting has advantages because you can use a root stock grape variety that has desired hardiness or disease-resistance characteristics and graft a different variety with the fruit-bearing characteristics you want as the top growth. You can also use grafting to change established grape vines so that they bear a different variety of grapes on currently healthy trunks and root systems. To graft Concord grape vines, you need vigorous root stock suited to your local growing conditions and Concord grape scion wood cuttings for the fruit-bearing branches. You should do grafting work in late winter while the grape vines are dormant.
Gather scion wood from healthy Concord grape vines in January or February. Select canes that previously grew in full sun with healthy buds that have not suffered freeze damage. Use canes that are about 1/4 inch to 1/2 inch in diameter. Allow two buds per graft and two grafts per trunk. Place the cut ends of the scions in moist towelling until you are ready to graft each piece.
Cut the trunk of the existing vine you will use as root stock to the desired height for the placement of the grafts using a pruning saw or loppers. Clean up debris to prevent spreading diseases.
Use a pruning saw to make two small cuts through the bark and slightly into the cambium layer near the base of the trunk, one cut on each side of the trunk. Make the cuts about 1/4 inch deep. The trunk will "bleed" sap through the cuts. Make the cuts before you graft or the sap flow will dislodge the grafts.
Cut the scion canes into sections with hand pruning shears. Each section should have two viable buds. Keep the scion sections moist in wet towelling.
Make a 30 degree diagonal face cut on the trunk by beginning about 2 inches from the top of the prepared trunk and drawing the knife up to the cut top edge. The face cut should expose the cambium layer with the bark removed. Prepare the grafting face further by making two incisions about 1 inch long downward into the cambium of the face cut. Prepare a face cut on the opposite side of the trunk for the second graft.
Make a long diagonal face cut on the bottom end of the scion that matches the length of the face cut on the trunk. Turn the scion over and make a steeply angled cut across the tip of the first scion cut to create a flat point. Beginning in the centre of the scion face cut, make an incision about 1 inch long to "split" the scion face cut. Repeat with another scion for the second graft.
Hold a prepared scion so the face cut meets the face cut of the trunk. Open the slit incisions of the trunk and the scion slightly, and slide the scion section into place with the outer bark of the scion exposed and the inner cambium layers of the scion and the trunk interleaved. Repeat with the scion of the second graft.
Wrap grafting tape around the trunk to secure the scions. Paint grafting sealant over all wounds. Paint over the grafting tape.
A face cut prepares flat, layered surfaces on the trunk and the scions. The flat surfaces are the areas that will heal together to complete the graft. Hold the scion correctly and gently tap it into place if necessary. The face cuts must make solid contact.
The cambium transports nutrients from the roots to the grafted branches. The cambium layers of the trunk and scion must have contact or the graft will not grow.