June-bearing red raspberries will grow naturally in a hedgerow system, as Figure 7.1 illustrates.
June-bearing Red Raspberries
The suckers, originating from the root system, will fill in the entire length of the row. No summer pruning (except for spent floricane removal) is necessary, although suckers growing outside the 12-inch hedgerow may be removed at any time. March is the best time to prune in Pennsylvania because any cane dieback from cold will be apparent; however, raspberries can be dormant pruned any time canes are fully dormant. In the dormant season, remove canes outside the 12-inch width of the row, thin canes to 6 to 8 inches between canes, and top remaining canes to 48 to 60 inches in height, removing about one-fourth of the cane. Be sure to retain those canes with the largest diameter.
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
Everbearing Red (or Gold) Raspberries
Everbearing red (or gold) raspberries should be mowed to a height of 1 to 2 inches in the dormant season. Although some gardeners prune them like June-bearing red raspberries to obtain the spring crop (only about 10 percent of the total crop for Heritage), it is more practical to plant some of the June bearers if a spring and a fall crop are desired.
Trailing blackberries should be summer tipped at about 6 inches above the highest trellis wire and tied to it during the summer months. For dormant pruning, select five to eight of the strongest canes, remove all laterals originating on the lower 3 feet of the canes, and tip back remaining laterals to 12 to 18 inches.
The home garden environment provides some unique opportunities for trellising. Consider growing thornless blackberries along a split-rail fence, or use thornless blackberries or black raspberries as a screen on a 6-foot fence. You are limited only by your imagination!
Trellis systems generally do not affect the type of pruning a plant receives. In other words, black and purple raspberries still require summer tipping, but the trellis determines the height of tipping. Trellises allow plants to support more surface area for fruit production. Several trellises have been experimented with successfully. See Figure 7.3 for possible trellis designs.
Figure 7.3 Raspberry trellis systems: (A) the "l" trellis; (B) the "T" trellis; (C) the "V" trellis