Effect of planting time and short-day treatment on growth and flowering of Dahlia imperialis .

摘要

Dahlia imperialis was once solely cultivated in botanical gardens in Japan, but recently it is also being cultivated in home gardens. It can be problematic that the plant flowers late and grows more than 3 m. The cuttings of Dahlia imperialis were planted at 1 m intervals in a field or in a plastic container measuring: width 35 x length 50 x height 30 cm (capacity of 52.5 liter) on May 11, June 11, July 10 and August 7, 2001. The stem elongation showed a sigmoid curve. The stems grew slowly during the high temperatures recorded in June and August, and the stems elongated rapidly from September when night temperatures dropped with elongation ceasing with commencement of flowering. It was generally surmised that stem length, the number of flowers produced, and the duration of flowering was better if planted early. Plants cultivated in the glasshouse produced very few flowers. Light intensity through the glass and limited root zone are two probably factors. The short-day of 10 hours treating Dahlia imperialis planted in Wagner pot (0.05 m2) and planted at 1 m interval in a field were assessed for stem length, number of flowers and duration of flowering. As for the plants treated early with short-day and for a long time, flowering was hasty and maintained a longer flowering period.