image by Acme: Flickr.com
Pruning blackberry bushes helps control and direct their growth. It also increases the production and size of the berries. Blackberry cane growth is a two-year cycle. In the first year a non-fruiting cane, called the primocane, is produced. In the second year, the primocane turns into a floricane. This is the cane that produces flowers and berries. The floricane dies after it produces berries.
Prune lateral branches to 16 inches long in the early spring. This encourages the blackberry bush to produce more branches and create a bushier habit.
Remove any scraggly growth from around the crowns of the blackberry bushes. These are canes that are not useful in the production of berries. Eliminating them will allow more light to reach the crowns.
Cut the primocanes back to 3 to 4 feet in midsummer. Remember that the primocanes are canes without flowers and are next year's berry crop. Cutting back the primocanes allows more energy to be directed into berry production.
Remove any dead branches when it is obvious that they are lifeless. Look for brown canes that are easy to snap off amid new green growth. This will help prevent disease.
Prune the floricanes down to the ground after they have stopped bearing fruit. This will redirect the growth into the primocanes for next year. It will also result in less work in the spring when you are clearing away dead canes.