Answer: Blackberries just ARE big, but regular pruning and training can help a lot both with size control and with fruit production. In winter or early spring, canes that have completed their second growing season should be removed to make way for new growth. They can be distinguished by their old, crackling bark. The canes that sprouted the previous summer will bear the fruit this coming year. Each winter, remove two year old canes (the ones that bore fruit last year) and any excess and/or weak 1-year-old canes at the ground. Then prune back the remaining canes to 4 to 18 inches to make them stronger (leave the thick ones longer). Leave only six or eight first-year canes spaced four or six inches apart per clump. If the plants have suckered or spread wildly, you can also dig up and remove the excess plants.
Besides pruning, you can try training them in a row between two parallel wires set on posts (hold the wires apart like an old fashioned laundry line), or tie each clump loosely to a tall stake. Either of these is easier to pick through than a cage.
Good luck with your berries!
Q&A Library Searching Tips