This test planting, made early last year, looked like this already in July. Greg Lang shows off a UFO tree.
Tall Spindle Axe—In this system, the central leader is the only permanent wood, and it is not headed until full tree height of about eight feet is achieved—and perhaps it won’t need to be headed at all before full fruiting commences. The rest of the tree is made up of temporary fruiting wood that is to be renewed on a five-year cycle (20 percent per year). The largest limbs will be cut back to a basal bud from which a new branch will grow. Buds need to be selected (with nonselected buds removed), or perhaps induced with scoring or Promalin (gibberellins and benzyladenine) treatments, to build uniformly distributed tiers of fruiting wood.
Sweet cherries fruit differentially on year-old and two-year-old wood, Dr. Greg Lang of Michigan State University reminded growers on a recent cherry tour in Michigan. Trees will fruit first from buds at the base of the previous season’s growth. The next year, fruiting will occur at spurs all along the two-year-old (and older) section of branch. The length of this “fruiting unit” needs to be controlled annually, cut back 15 to 30 percent, as a means of balancing future fruit production and thus optimizing fruit size.
As seasonal branch growth slows, nodes become closer and closer together, Lang said. Those large clusters of fruit that would develop toward the end of branches can overcrop the tree and depress fruit size, hence the benefits of annual heading to regulate future crop loads.
Slender Spindle Axe—Very similar to tall spindle axe except for their annual pruning, these trees were set twice as close (30 inches apart), and the branches are kept even shorter. Much of the fruit is borne on basal buds of the previous season’s new shoots, as close to the trunk as possible. This is accomplished through “short-pruning” all previous season shoots to the basal flower buds plus the most basal one or two vegetative buds (which will regrow the shoot). Lang is keeping track of Stefano Musacchi’s work in Italy, where trees pruned this way have remained fruitful for nine years so far.
A key challenge is to develop enough short shoots to promote fruiting units rather than strong branches, since fruiting occurs right at spurs and short branches off the trunk; this will likely be influenced not only by rootstock but also variety, Lang said.
Kym Green Bush—This bushlike tree is created by heading the whip to encourage four or five buds, then repeatedly heading back new growth, two or three times over the first couple of years, until 20 to 30 upright fruiting branches are achieved. It takes an extra year to build this structure, Lang said, but the result is a tree that fruits on upright growth, which is renewed on a five-year cycle by removing the largest fifth of the branches each year. Only the short trunk is permanent. In its fruiting pattern, it is similar to the Upright Fruiting Offshoot system, with the majority of the fruit borne on spurs along each upright fruiting unit, and removal or “short-pruning” of any laterals to prevent shading.
Upright Fruiting Offshoots—In this system, a tree is planted at an angle (45 degrees seems best, based on research by Lang’s current graduate student Tiffany Lillrose), then the whip is bent down and fastened to a wire about 21 inches above the ground. Buds along the bottom are rubbed off, and a dozen buds, preferably right on top and evenly spaced, are encouraged to send shoots upward. These uprights are the fruiting units, and one fifth of them, the largest, are removed every year to develop new upright replacement shoots on a five-year cycle.