Seasonal extension of glasshouse blackberry and raspberry with supplemental assimilation lighting

In Belgium, raspberry and blackberry crops can be harvested from early May until mid-November. This is made possible through a combination of cultivation systems and cold storage of the plants. With additional assimilation lighting, the season could be extended even further to avoid peaks of high supply on the market. Trials with LED lamps were conducted to test the possibility of extending the raspberry and blackberry season. The target period for illuminated crops for blackberry was late autumn and early spring for raspberry. To initiate early production of raspberries in January, plants were placed in a glasshouse from October-November. Different cultivation methods, plant types and ages were compared to find out which plant material was most suitable for illuminated cultivation during the winter. For raspberry, fresh plant material, planted in the same year, resulted in the best fruit quality and yield compared to overwintered shoots, planted the year before. For blackberry, old planting material planted the previous year and stored for 8 months in cold storage, outyielded young plant material by 20%. On the other hand, old plant material, having been cold-stored for long periods are expensive and prone to plant quality decline. Using LED assimilation light, different light intensities (110 and 180 µmol m^‑2 s^‑1) were compared in combination with light strategies. The current study shows that yield improves with increased light intensity, a result most clearly observed in raspberries. For blackberries, the additional production does not justify the higher costs of the high light intensity. After studying cropping system profitability the lighting strategy was adjusted. The number of hours of illumination per day could be reduced by switching lights off in the afternoon. In doing so, negative effect on production was observed. Additionally, fruit quality improved. By turning off the lights when natural solar radiation was already sufficient, sunburn incidence was reduced, and fruit firmness was improved. Early forcing of raspberry invariably resulted in poor bud break. Putting raspberry plants in cold storage too early meant that plants were not fully dormant and flower induction incomplete. Subsequent experiments aimed to improve bud-break by varying the amount and timing of chill. No measure taken had a significant effect on bud break. Further research needs to be done to find the cause of uneven bud break in forced raspberry cultivation.