Blueberry bushes fit well in the schema of the gardener with a long-term vision: they require time on the order of years to become established and bear a rewarding crop of fruit. Though berry yields will be lower in the first few years after planting, proper pruning of your blueberry bushes will increase the overall fruit size and yield within several years, and is necessary for a vigorous, healthy shrub.
In general, the late winter months from January to March are the best time to prune blueberry bushes of any age or variety. Plants are completely dormant during this time. Southern climates may have earlier frost-free dates, so gardeners there should prune earlier rather than later, or risk pruning green wood.
Trimming away weak, sick, diseased and dead canes off otherwise healthy blueberry bushes encourages growth of new wood and promotes vigor. Branches that are low and near to the ground can sap energy from the taller upright canes, or branches, which are better suited to fruit production. Pruning also opens up the structure of the shrub, allowing sunlight and airflow into the middle of the bush and onto fruit.
Prune young bushes, from 1 to 4 years old, relatively heavily to discourage the shrub from bearing any fruit at all. This allows the plant to concentrate on root growth and strengthening existing canes. The remaining canes will grow thicker, and once the bush is allowed to set fruit, the resulting crop will generally have larger berries than a bush allowed to fruit without first being pruned.
To prune, target the tops of canes where fruit buds form, twig shoots lower on the main branches and any weak or low-growing shoots.
Three to 10 years
Mature bushes---3 to 10 years old---do not need to be as heavily pruned as young shrubs. Gardeners should aim to cut back roughly 20 percent of new cane growth at the crown, keeping the plant at a manageable height.
As with a younger shrub, old, weak or low-growing shoots should be pruned away completely, as well as twigs in the interior of the bush. These small branches not only clutter the heart of the blueberry bush, but also draw resources away from fruit buds and leaves on the ends of the main branches.
Older Than 10 Years
Most varieties of blueberries begin to decline after 10 years of age. By pruning an older bush back severely, or cutting off all canes to within 2 to 3 feet of the ground, you can rejuvenated the plant for another several years.
One way to accomplish uninterrupted fruit yields is to plant new bushes when older ones begin to exhibit symptoms of age and decline. By the time the younger bushes have gone through several years of pruning, they will be of fruiting age, and you can remove the older bushes.