Japanese maples (Acer palmatum) are a favorite garden plant for many. If you've every dreamed of propagating your own, it may be easier than you think. These small, graceful trees grow in U.S. Department of Agriculture plant hardiness zones 5b through 8b and are typically propagated by grafting. This time-honored technique involves splicing a cutting from a particular variety of Japanese maple onto the "rootstock" of a seedling variety. The rootstock conveys vigor and health to the tree and the cutting, also called the "scion" wood, grows into a tree that is an exact replica of the one from which the cutting is taken. Late winter is the best time to graft a Japanese maple.
Bring the "rootstock" plant indoors several weeks before grafting. You want the plant to "wake up" from dormancy so it will feed energy to the "scion" after it is grafted. The best rootstocks are seedlings of the basic Japanese maple species (Acer palmatum), which are available in some nurseries or online plant catalogs.
Collect the "scion" wood from the Japanese maple you wish to propagate. Take cuttings of branches that are about the size of a pencil and divide them up into 6- to 12-inch pieces. Make sure to keep track of which way the cuttings were oriented on the tree. When you graft, the end of the cutting facing up needs to be the same end that was pointing toward the growing tip of the branch on the tree from which it came.
Cut the bottom of each cutting into a "V" or wedge shape with a grafting knife. The total length of the cut should be 1 to 2 inches. A cut with the inverse shape needs to be made in the trunk of the rootstock, about 4 to 6 inches from the soil line. If the trunk of the "rootstock" is a larger diameter than the "scion" cuttings, make the wedge-shaped cut into the side of the trunk. If it is approximately the same diameter, cut the rootstock down to the point where the graft will be made and then make the wedge cut directly into the top of the remaining stem. The goal is to for the inner bark layer of each piece of wood, known as the "cambium," to line up perfectly and remain in close contact. The more each cut can be the true inverse shape of the other, like a hand inside a glove, the more likely it is for the graft to be successful.
Slide the point of the wedge-shaped cut on the bottom of the "scion" firmly into its counterpart on the "rootstock." Wrap grafting tape tightly around the union, being careful not to move the position of the "scion." Wrap it 10 or 12 times, securing it on the final go-around by tucking the tail of the grafting tape under the last wrap and cinching it tight.
Coat the entire area around the graft union with a sealant used for tree wounds to trap moisture in the graft and keep disease organisms at bay. Avoid getting any of the sealant between the point of contact between the cut ends of the "scion" and "rootstock."
Keep the grafted Japanese maples in a sunny window and water them whenever the top 1/2 inch of soil becomes dry. It should be apparent within a few weeks if the grafts have taken. There is rarely 100 percent success with grafting Japanese maples -- try more grafts than you actually need and don't be discouraged if some of them don't make it.
Once the weather has warmed in spring and all danger of frost has passed, place the Japanese maple in a partially shaded location outdoors. Allow it to grow for the season in its pot and then transplant it to a permanent location in fall or the following spring.