Blackberries Cut away old canes and reduce the number of new ones. Trailing blackberries are usually trained to a trellis. After pruning, allow each season's new canes to trail on the ground, where they won't crowd fruiting canes. Alternatively, train new canes on one wire or in one direction along the trellis, and train fruiting canes along the other wire or in the other direction. Red and Yellow Raspberries Fruit stalks grow on the canes, not on branches.
Longer canes produce more fruit.
How much to shorten them depends on your trellising method. You can surround the rows with two rows of wire strung between posts at each end of the row at 2 and 5 feet above the ground. Either tie the canes to the wires and shorten them to about 6 feet, or leave the canes nearly full length, then bend them along and around the upper wire. Everbearing Brambles Prune everbearing types of red and yellow raspberries as you would prune the summerbearing kind, with one difference. The year-old canes will have started fruiting at their ends late the previous year and will finish fruiting lower down the second year.