Prune blackberry bushes by trimming the tips in the spring and removing the canes that produced berries in the fall. Cut away any dead, infested or diseased blackberry canes as soon as possible to prevent damage to the bush.
Pruning in the spring is called tip pruning. This process encourages the blackberry bush to branch out, not up, resulting in more berries during the summer. Tip prune the bush by snipping off the canes to approximately 24 inches high. For smaller canes or for newly planted blackberry bushes, cut off the first 1 to 2 inches of the growing cane.
In the late summer or fall, blackberry bushes need a cleanup pruning. The purpose of this type of pruning is to remove the canes that have produced berries to allow new shoots to grow. Because blackberries only grow on two-year-old growth, cleanup pruning is essential. Cut all of the canes that grew berries down to ground level. Cleanup pruning helps bushes to produce more blackberries in subsequent years.
Because blackberry bushes are susceptible to disease, it is crucial to properly dispose of pruned canes. Any diseased or infested canes should be burned or hauled away in order to prevent reinfection.