For adequate pollination, plant at least two varieties together. Since most varieties of Japanese and American plums are self-unfruitful, plant two or more varieties together. Occasionally, certain fruit trees such as apples bear heavily one year and sparsely the next. The spring-flowering buds of most hardy fruit trees have actually been formed during the previous summer. Therefore, an especially heavy crop one year may prevent adequate bud formation for the following year.
Biennial bearing is difficult to alter or correct.
However, you can induce a return to normal yearly fruit production by early and heavy thinning during the year in which the trees are producing their large yield. About 30 to 40 healthy leaves per single fruit are needed to produce good quality. Within 30 days after bloom, thin remaining fruit to leave a single fruit every 6 to 8 inches along the branches. Avoid placing fruit trees where they will be shaded by buildings or by other trees. Leave adequate space for fruit tree root systems by planting away from shade or forest trees.