In regions with a mild climate, primocanes of the cultivars 'Prime-Jan' and 'Prime-Jim' can produce harvestable fruit by mid-September. In the experiments reported below, 'Prime-Jan' plugs were planted either in the open field or in an uncovered Haygrove high tunnel in western Oregon, USA, in May.
The following spring, half the primocanes were cut to ground level when they were either 0.25m or 0.5m tall, while others were left intact. When the canes were 0.5m tall, about 5cm of shoot tip was removed (soft-tipping) to encourage branching. Branches were also soft-tipped in one treatment.
Harvesting began in September but was delayed for a month if the canes were cut when 0.5m tall. The tunnel was roofed with Luminance THB in autumn and fruit was still being harvested from it in mid-November.
The yield from the open field was 9 tonnes per hectare but more than 18 tonnes per hectare was produced from the tunnel when both the canes and their branches were soft-tipped.
Primocane-Fruiting Blackberries: Potential for Extending Harvest Season and Production Regions by Strik and Thompson (2009). HortScience 44 (1): 23-24. High Tunnel Versus Open Field: Management of Primocane Blackberry Using Pruning and Tipping to Increase Yield and Extend the Fruiting Season by Thompson, Strik, Finn, Zhao and Clark (2009). HortScience 44 (6): 1581-1587. ISHS members can view HortScience at www.ishs.org.