Abstract:Iris germanica ＇Royal touch＇ was used to investigate the effects of 5 different photoperiods on flower bud differentiation and photosynthesis. Short-day treatments accelerated the flower bud differentiation, whereas long-day treatments increased the numbers of the flower buds per inflorescence. The photosynthetic capacity per unit leaf area was higher in long-day treatments. Flower bud differentiation had a significantly positive correlation with leaf area, leaf dry weight, and the ratio of above： below ground biomass, respectively. These results suggested that effects of photoperiods on flower bud differentiation and numbers are related to plant biomass and photosynthesis.