Growing Degrees Days Requirements on Phenological Principal Growth Stages of Rubus Idaeus Cultivar Polka and Tulameen in Urban Garden

In the current context of climate change, research must focus on testing cultivars capable of tolerating wide ecophysiological variations throughout the growing season. This study assessed the growing degree day (GDD) requirements for key BBCH phenological stages and the productivity of two red raspberry cultivars, Rubus idaeus ‘Polka’ and ‘Tulameen’, grown in an urban garden. Field experiments included three nutrition areas: maximum (100 cm, MaxNA), medium (75 cm, MedNA), and minimum (50 cm, MinNA). Phenology and productivity were recorded every three days across the growing season, while GDD and precipitation were derived from climatic data. ‘Polka’ showed about 40% higher productivity in MedNA during the second decade of August, whereas ‘Tulameen’ followed a similar trend one month earlier. During the first acclimatization year, all ‘Tulameen’ plants survived across treatments, while ‘Polka’ failed to survive in MaxNA. Average GDD values during the vegetation season reached 5800°C in MedNA for ‘Tulameen’ and in MinNA for ‘Polka’. Overall, ‘Tulameen’ demonstrated higher survival but lower yield, while ‘Polka’ exhibited greater productivity—over tenfold higher—despite reduced survival. Results indicate that in urban gardens, variations in GDD and precipitation influenced the phenological development and yield performance of raspberry cultivars tested.