Annual pruning of mature blueberry plants is necessary if you want to keep them productive. Blueberry bushes produce flower buds the year prior to flowering. This means flowers that bloom this spring were set last summer on new wood. Therefore, if the plant is not pruned and fertilized to promote new, vigorous growth, much of the plant's energy will be used in maintaining tall, woody, nonproductive growth. The time to do the pruning is late winter to early spring.
Pruning Terminology
A rule of thumb is to not have any stem on the plant more than five or six years old. One way to determine the age of a stem is to look at the bark color. New stems are green to reddish. Two-year-old stems are reddish to light brown. Three-year-old stems are light brown to gray while older stems are gray and the bark may be starting to flake off The number of stems in a mature plant is usually kept between four to seven.
To prune highbush blueberries correctly, it is essential to know their bearing habits. Most of the flower buds, each containing from five to ten flowers, are borne on the top portions of the current season's growth (Figure 1). The buds are formed in the axils of leaves during the late summer and early fall then bloom and produce fruit the following year.
Figure 1. Notice the difference between the large flower buds and small leaf buds.