Grafting to crabapple trees diversifies orchards by introducing new varieties of apples and crabapples without planting new trees. Growers take advantage of the crabapple's hardiness and disease resistance by grafting less rugged fruiting varieties to established trees. The type of scion--a cutting from the desired cultivar--grafted to the tree determines the flowering habit and the type of fruit. The rootstock of the crabapple determines the size of the tree at maturity.
Collect or purchase healthy apple or crabapple scions in late winter when trees are dormant. Use pruning shears to cut the scions to 8-inch lengths with at least three buds each and store between moist layers of paper towels inside sealed zip-top bags. Refrigerate the scions until needed.
Select an upright trunk or an upward leading branch 1 or 2 inches in diameter and between 4 and 6 feet from the ground to serve as the site for the graft. Using a pruning saw or limb loppers, saw the limb or stem straight across at least 8 inches from a main fork or the junction with the trunk.
Place the edge of the grafting knife across the end of the branch stump and strike carefully with a wooden mallet to slightly split the grafting site. Hold the split open with a narrow wooden wedge.
Select two scions of the same diameter. Sharpen the base of the scions to a wedge shape with two converging 1 1/2-inch long diagonal cuts. Blunt the point of the scion wedges by trimming the tips back 3/16 inches. Bark could peel away from scions cut to a sharp point. Wedge the scions into opposite sides of the split, lining up the bark on the scion with the bark of the branch stump. Remove the wooden wedge that held the cleft open.
Seal the end of the crabapple branch with grafting wax. Seal the split section below the scions with wax, but be careful not to force the scions out of position. Wrap the limb from top downward with grafting tape, ending 2 inches below the split section.
Cover the graft with aluminum foil to form a seal around the base of each scion. Place a plastic bag over the graft, forcing the scions carefully through holes cut in the bottom of the bag. Secure the bag below the graft with grafting tape.