Effect of nutrient solution composition on growth, flowering, nutrient status and cold hardiness of Rhododendron yakushimanum grown on ebb-and-flow benches

Growth, flowering and cold hardiness of Rhododendron yakushimanum 'Blurettia' and 'Percy Wiseman' cultivated on ebb-and-flow benches and flooded with six different nutrient solutions was compared to plants fertilized with controlled release fertilizer (2 g L-1 Osmocote 15-9-9) under overhead irrigation. The following nutrient solutions were used for fertigation 60-20-60, 120-20-60, 180-20-60, 120-40-60,120-60-60 and 120-20-120 (N-P-K levels in mg L-1). 'Blurettia' plants fertigated with the highest N level were higher then in other treatments including controlled release fertilizer but number of leaves per plant was not affected. The lowest N level decreased both height and number of leaves of 'Percy Wiseman'. In both cultivars low N level as well as fertilization with controlled release fertilizer resulted in poor flowering. Also, increased P and K levels reduced number of flowers per plant in 'Blurettia' but in 'Percy Wiseman' the opposite was true. Overall EC values of growing media were several-fold higher in pots fertigated with ebb-and-flow system then in these given overhead irrigation and fertilization with Osmocote. In contrast, pH increase in the medium was more evident under overhead irrigation. Subirrigation resulted in significant salt accumulation in the upper part of growing medium even though plants were cultivated outdoor and some leaching due to rain should be expected. Nutrient content of leaves generally reflected composition of nutrient solution. However, plants fertilized with controlled release fertilizer had relatively low P and high Ca content in leaves. High N and K levels increased cold hardiness of Rhododendron leaves compared to both low N nutrient solution as well as Osmocote treatment.