Blackberry Long-cane Cold Storage and Forcing Strategy Effects on Flower and Fruit Development

Blackberry ( Rubus subg. Rubus) production using soilless culture and “long-cane” techniques offers growers the potential to achieve off-season harvests and increase yields. This study investigated the feasibility of achieving early spring harvests and high yields with four blackberry cultivars (Natchez, Ouachita, Prime-Ark ® Freedom, and Prime-Ark ® Traveler) grown using long-cane techniques and six different cold storage and forcing environment strategies. Long-cane blackberry plants were container-grown outdoors during 2020 and were overwintered either at an outdoor nursery or in a cold storage facility (4 °C). Dormant plants were then forced the following spring at the outdoor nursery location or in a heated greenhouse. The time (in days) and accumulation of heat units (growing degree days) at first open flower and ripe fruit were measured for each cultivar and strategy treatment combination in addition to marketable yield. Time to first flower and fruit ranged from 21 to 125 days and from 62 to 173 days, respectively, and depended on cultivar and strategy. Accumulated heat units at first flower and fruit also varied by strategy for each cultivar. Marketable and total harvested yield by cultivar were (g/plant) 430 and 1028 for ‘Natchez’, 387 and 1046 for ‘Ouachita’, 320 and 680 for ‘Prime-Ark ® Freedom’, and 417 and 993 for ‘Prime-Ark ® Traveler’, respectively. Overall, yields were low compared with reports from commercial industry and varied between cold storage/forcing strategies. This study showed that forcing long-cane blackberry crops in protected structures can decrease crop timing for an early spring harvest, provided the structure sufficiently raises the average daily temperature to increase plant development rates. It also highlighted the importance of environmental conditions and cultural practices on fruit yield and quality in long-cane production.