Yield, quality and vase life of cut roses in year-round greenhouse production

Abstract

Year-round greenhouse production of cut roses expanded rapidly in Finland in the 1990s.The use of supplemental lights increased substantially, and in terms of cultivation technique, the traditional upright growing technique was accompanied by the new shoot bending technique.These changes generated new challenges for growers, increasing their need of information about year-round cultivation.The objective of this study was to improve the yield, quality and vase life of greenhouse cut roses in year-round production, with an emphasis on winter-time cultivation.Different growing conditions, growing techniques, cultivars and plant characteristics were studied as determinants of yield, quality and vase life.The effects of different light intensities and daily durations of supplemental lighting on yield and quality were examined.Supplemental light at 65 mol m -2 s -1 PPF (photosynthetic photon flux) was insufficient for winter cultivation with a rest period in mid-winter, and correspondingly, 100 mol m -2 s -1 PPF was insufficient for uninterrupted winter cultivation as far as the quantity and quality of yield are concerned.Lighting at 220 mol m -2 s -1 PPF for 20 h d -1 gave a high yield in dense plantation through all seasons.The efficiency of the duration of supplemental light was dependent on PPF and cultivar.The duration of the rest period and rate of temperature raise at forcing interacted on the yield and quality of young 'Mercedes' plants.Two of the studied combinations resulted in high yields: a 6-week rest period followed by a rapid temperature raise at forcing, and a 2week rest period followed by a slow temperature raise.These results suggest that physiological changes may take place in plants between the second and the sixth week of the cold period which subsequently affect the response to forcing temperature.Pruning, which is usually done in traditional upright growing method, was compared with the shoot bending technique at the beginning of forcing after the rest period.Pruning leaves the plants almost or completely leafless, while bending retains the photosynthesizing leaves in the plants.In comparison with pruning, shoot bending increased yield quantity and shoot length in 'Mercedes' and 'Frisco'.Blind shoot bending was also compared with shoot cutting after harvest.Bending increased the yield of 'Mercedes' but not that of 'Frisco', which is a more vigorous cultivar than 'Mercedes'.Length of the flowering shoots was, however, increased by bending in both cultivars.In the traditional growing technique, leaves remaining on the mother canes after harvest seemed to support good flower production in strongly growing cultivars.Hence, harvesting height is of importance.Combined effects of various bending and harvesting heights on the yield quantity and quality were also investigated.High bending and high harvesting height at the beginning of cultivation resulted in an increased number of flowering shoots.This combination gave a crown with leaves and a high number of good quality bottom breaks, which are necessary for good flower production.Leafy plants did not need many bent shoots simultaneously; 1-3 shoots were enough.High harvesting height decreased the percentage of long flowering shoots compared with low height.Dense plantation in shoot bending growing technique ensured high production.The growing technique had a minor effect on vase life.Cultivation conditions had varied effects on vase life.The duration of supplemental light affected vase life differently, depending on the cultivar.Daily light duration and different number of night-time breaks in lighting affected the vase life of 'Frisco'.Increased risk for short vase life seemed to be associated with high plant level variation within treatments.Estimation of plant specific hazards might provide us with new insights for understanding the flowers' behaviour in vase.