Red and black raspberry production is common in the north, but blackberry production is almost non-existent as they have long been considered too tender for northern commercial production. With the development of the Rotating Cross-Arm Trellis, we can capture this lost market.
Primocane-fruiting blackberry varieties have been released in recent years which offer an opportunity to add to fall sales, but the question most growers ask is: “Is it worth it?”
Most commercial blackberry varieties are rated cold hardy to zone 6 or even 5, however this can be a misrepresentation. Cold hardiness refers to crown survival rather than bud survival. Buds higher on canes are more susceptible to damage. This greatly affects yields and picking heights, as berries produced on unprotected plants are typically on low buds, making picking difficult.
The Rotating Cross-Arm trellis (RCA) is a modified V-trellis with one long and one short trellis arm, and removable pins to permit post rotation. This allows growers to change the architecture of the plant, and to lay canes close to ground level and cover with a heavy row cover - significantly increasing winter protection.
On the RCA, primocanes are grown horizontally along a low wire, 16” high. When canes reach the next plant, they are tipped, and leaves are removed to encourage lateral bud break. Prior to floricane removal, primocane laterals are draped untethered over the wire on the short trellis arm. After removal, laterals are trained vertically to wires along the long trellis arm and primocanes are shifted from under the short trellis arm to under the long trellis arm. This pruning and training technique not only allows for trellis arms to be laid down and covered for winter but when placed parallel to the ground prior to flowering it forces most flowers to one side of the trellis, increasing picking efficacy and decreasing sunscald. This works best when the RCA is oriented East West.
Multiple primocane blackberry varieties have been released from the University of Arkansas, beginning in 2004. Like raspberries, primocane fruiting blackberry canes emerge in spring, fruit in the fall and can be mowed after fall harvest however yields are considerably lower than their floricane counterparts. Different heights and numbers of soft pinching have been tested to increase yields, however in colder climates the season is too short for this technique to be successful. Unfortunately, northern growers have found that these plants fruit too late leaving much of the crop unharvested. High tunnels can extend the picking season however it is unlikely that increased yields or higher berry prices would justify this cost.