Abstract: The limited inductive photoperiod，photoperiod sensitivity at different developmental stages，and the effect of photoperiod on visual quality of potted plants were studied in the long-day plant Calceolaria × herbeohybrida Voss‘Dainty’by transferring plants between short day and long day conditions. The length of juvenility was also studied. When plants were transferred from 7 long days to short day conditions，the days of flowering were significantly longer than those transferred from 14 to 42 long days. When transferred during 14 long days to 42 long days，plants flowered almost at the same days. These results indicated that flower bud development of‘Dainty’may be insensitive to photoperiod under 14 long days，and that 7–14 long days may be the limited inductive photoperiod that is sufficient to promote flowering. When plants were transferred from 7 long days to short day conditions，days when buds become visible decreased and days from visible bud to flowering increased because apical bud aborted and lateral bud developed and flowered. These results indicated that 7 long days promoted flower initiation and that flower bud development was sensitive to photoperiod during this time period. Long days enhanced plant height，main stem length，flowering uniformity and visual quality of potted plants. When plants were transferred from long day to short day conditions，the later the plant were transferred，the heavier the upper ground part，the root，and the total plant were. The reverse results were observed when plants were transferred from short day to long day conditions. The juvenile stage ended when the plant had 3 pairs of leaves under experimental conditions. In practice，reasonable management of photoperiod can be employed to control flowering time with acceptable quality. If seeds of‘Dainty’are sown in early September and treated with at least 21 long days at 3-leaf-pair stage，they can flower in early January to meet the market demand of Spring Festival.

Key words: Calceolaria × herbeohybrida Voss, limited inductive photoperiod, photoperiod sensitivity, flower development, visual quality of potted plants