Training and pruning blackberries are necessary to help them adjust to the trellis, remove infected, damaged, and weak canes, improve light penetration and aeration, boost bud development (yield), and retain the shape of the plates, facilitating cultivation activities (e.g., harvesting).
The way we prune depends on the variety of blackberries (architecture, tendency to produce suckers, etc.) and the trellis system used. The training during the establishment year will differ if bare-root canes or container-grown plantlets are used. In all types, suckers should be removed when grown far from the plant's crown (6-8 in both directions). Primocane-fruiting blackberries requires different pruning approaches based on the desired crop yield. For one single production per year, you can cut all canes to the ground after harvest. For two crops, you can trim canes after the primocane harvest to just below the fruiting point; the remaining portion will produce the next year's floricane crop. Ensure all dead canes are removed for optimal plant health and productivity.
Erect and Semi-erect Blackberries tend to grow long canes. As a result, the farmer needs to tip the plant's primocanes during summer when they reach 30-36 inches (up to 48 in) (76-90 cm, up to 121 cm) height to promote lateral branching. Tipping can be performed 3-4 consecutive times per season by using hand tools or specialized machines. The laterals should be shortened to 12-24 inches (30-60 cm) long in early spring to promote the production of larger fruits and facilitate harvest. As the new canes emerge and grow during spring, the farmer needs to tie them into their support (wires or trellis), if any is used.
Thinning is needed during plants' dormancy. You can keep 7-8 vigorous canes per hill (5-6 per foot of row), up to 5-6 feet (1.5-1.8 m) tall, and spread them in the trellis in a fan pattern (multiple straight branches fanning outwards) (picture 1). Support can keep the canes more manageable, and you can harvest them more easily.
Due to the biennial nature of blackberry canes, the ones that produce fruits during summer (dying floricanes) should be removed from their base in fall.
Picture 1: Fan training pattern of erect and semi-erect blackberries
Trailing blackberries are usually not tipped but need to be trellised (two-wire systems). During the establishment year, allow the canes to grow. The farmer can choose 4 strong canes and tie them (interwoven) in the 2 wires (2 from one side and 2 from the other) (picture 2). Alternatively, he/she can leave the canes to reach the top wire and then weave them back down to the bottom wire and back up (picture 3). Canes need to be tipped only when they reach 8-10 feet (2.4-3 m) in length to keep the different plant canopies distinct.
(Picture 2 (left), Picture 3 (right): Training trailing blackberries
References
http://www.extension.uidaho.edu/publishing/pdf/BUL/BUL0812.pdf
http://extension.msstate.edu/publications/information-sheets/fruit-and-nut-review-blackberries
https://ag.missouristate.edu/assets/MtnGrv/B39GrowingBlackberriesinMissouri.pdf
https://www.rhs.org.uk/fruit/blackberries-and-hybrid-berries/pruning-training
https://extension.okstate.edu/fact-sheets/commercial-blackberry-production.html
Further reading
- Blackberry Nutritional Value and Health Benefits
- Blackberry vs Black Raspberry - Similarities and Differences
- Blackberry Plant Information - How to Identify Blackberries
- Site Selection, Soil Preparation, and Planting of Blackberries
- Blackberries Propagation and Pollination
- How to Prune and Train Blackberries
- Water Needs and Irrigation of Blackberries
- Nutrient Needs and Fertilization of Blackberries
- Blackberry Pests, Diseases and Weed Management
- Blackberry Yield, Harvest, and Storage