Black and Purple Raspberries
Black and purple raspberries require summer topping throughout the summer in addition to floricane removal. Black and purple raspberries should be topped at 36 inches, removing 3 to 4 inches of new growth (Figure 7.2). Do this two to three times during the season to top all of the canes as they grow. Topping encourages the development of lateral (fruiting) branches and increases the strength of the cane. (Note: Black raspberries will tend to have a very prostrate growth habit in the first year. If canes are pruned back in the dormant season, they will attain a more erect habit in subsequent years.)
For dormant pruning, remove all dead, damaged, and weak canes. Thin remaining canes to five to ten canes per plant. Lateral branches should be headed back to 4 to 7 inches (for blacks) or 6 to 10 inches (for purples). More vigorous plants can support longer lateral branches. All canes should be topped to 36 inches if they were not topped earlier.
Erect blackberries do not require trellising. They have, as the name suggests, very strong upright canes. They should be pruned similarly to black and purple raspberries; specifically, they should be headed back to 36 inches in the summer, with laterals cut back to 12 to 18 inches and canes thinned to 10 inches apart in the hedgerow during the dormant pruning.
Figure 7.2. Black and purple raspberry pruning (A) top the new canes at X; (B) laterals that develop after tip of cane is removed; (C) pruned plant with 6-8 inches of laterals left