Massive or minuscule, round or scraggly, spiky or smooth, all can describe members of this genus Yucca. Yuccas are adaptable plants of varying appearance that boom in U.S. Department of Agriculture plant hardiness zones 4 though 10. Perhaps the best known part of this Yucca clan is the Joshua tree (Yucca brevifolia) for whom a national park is named in California. It is possible to use grafting techniques adapted for fruit trees to meld a branch of a single Yucca cultivar onto the rootstock of another. The nearer the species, the greater the likelihood of success.
Saw off the yucca trunk or branch at a right angle to the grain. Select a trunk no more than 2 1/2 inches in diameter or a branch less than 6 feet from the bottom. If you decide to graft to your branch, choose an upright rather than a horizontal branch and make the cut no more than 2 feet from the yucca trunk. This part of the graft is termed the rootstock.
Drive a knife or grafting cleft into the cut end of the rootstock with a mallet, making a slit about 2 inches deep. Wedge the back end of this tool or a bit of rock into the cleft to hold it open.
Cut two scion pieces to graft into the rootstock; the scions are the components that make the branches, fruit and flowers of the Yucca. Prune the scions from sections of the previous season’s growth that are about one-quarter inch in diameter. Take cuttings about 6 inches long with at least three growth buds per scion, together with the smallest bud 2 inches from the bottom of the scion.
Use a grafting knife to remove a strip of bark beginning just below the lowest grass on the scion and continuing to the bottom end of the cutting edge. Turn the scion and repeat the cut on the other side of the basal end of the cutting edge. These cuts turn into the basal end of the scion into a rough wedge. Remove sufficient bark to expose the cambium, the layer of green wood just inside the bark. Ideally, the side of this basal wedge with the grass should be slightly thicker than the opposite side. Repeat this procedure using the next scion.
Catch the squeeze end of each scion into one side of the cleft from the rootstock. Position the pieces so that the smallest buds on each and every scion face out. Remove the tool you added to hold the cleft open. As the cleft closes, it will hide most of the cut surfaces of the scions.
Cover the graft area with grafting paint, including the entire cleft. After the first growing period, shorten or remove the weaker scion.