Effect of flower-bud stage and root pruning at onset of chilling on the flowering of forced and retarded tree peony [Paeonia suffruticosa]

This study was investigated to clarify the effect of flower-bud stage and root pruning at the onset of chilling on the flowering of a forced and retarded tree peony. The flowering percentage of ‘Shin Shima no Kagayaki’ was increased by advancing the stage of flower bud in forcing and retardation culture, even if the rootstocks of tree peony plants were pruned at the beginning of chilling. However, the flowering rate of ‘Shin Ka Jishi’ was low, regardless of the flower-bud stage. When plants with advanced flower-bud stage were forced after the chilling plants in pots without root pruning, the flowering percentage increased (80%) and cut flower quality was superior. Therefore, chilling the plant in a pot without root pruning is an effective method for improving the flowering rate of the cultivar, which is low in a forcing and retardation culture.