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.