Blackberry plants primarily grow as upright, self-supporting plants in the United States, but some varieties are trailing and need a trellis. Both varieties require trimming to produce the maximum amount of fruit. Blackberry plants will become unmanageable if they aren't pruned annually. Blackberries are biennial, which means the canes produce fruit in their second year of growth. Knowledge of how to trim these canes will help you to grow a productive and attractive bush.
Sterilize your pruning shears. Wipe down the blades with rubbing alcohol and a rag to minimize the spread of disease from one plant to another.
Cut weak and dead canes to the ground, after growth starts, to increase air circulation within the plant.
Trim first-year blackberry canes when they reach 24 to 36 inches in height. Cut off only the tips. This will encourage branching and increase fruit production.
Prune fruiting blackberry (second-year) canes to the ground after harvest. These canes eventually will die on their own, but pruning them is better for their health.
Destroy all plant material after pruning. This will minimize the spread of disease to or from the blackberry plant.