The key to splicing fruit trees is to start with two trees that are similar. Ideally, both the stock (the tree in the ground) and the scion (the tree that will be spliced onto the stock) should be of similar species, the same diameter and at the end of their first year of growth. Splicing should be done in early spring, between February and April when both trees are reaching the tail end of their dormancy. Successfully spliced fruit trees should begin producing new shoot growth in a week or so.
Choose the right trees to splice. The closer the trunks are in diameter, the more likely the the splice will be successful. Ideal fruit trees for grafting have diameters that fall between 3/8 and 3/4 inches in diameter and have at least 2 buds that are at least 6 inches long.
Cut off the stock tree's trunk 6 to 12 inches from the ground with a steep diagonal cut that is 3 inches long. Try your best to make the cut in one smooth stroke. Making a few cuts on a practice branch may improve your accuracy.
Make the tongue groove. Use the knife to make a cut that runs parallel to the trunk of the tree and starts 1 inch from the top of the diagonal cut and moves down to 1 inch from the bottom of the diagonal cut.
Cut the scion off its trunk at the same height as you cut the stock tree. Make the same diagonal and tongue cuts that you made in steps 2 through 3.
Match the diagonal cuts and tongues together. Slide the stock and the scion onto one another so that the tongues interlock and the spliced trunks fit snugly together. If the trunks were the same size to begin with, the parts will fit perfectly together and the spliced tree's trunk will look like it was never spliced at all.
Wrap the spliced section with grafting tape to hold it firmly together.