THE EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON FLOWERING OF PHYSOSTEGIA VIRGINIANA 'SUMMER SNOW' AND 'VIVID' AS POTTED PLANTS

We examined the effects of photoperiod and night temperature during forcing on flowering and plant quality of Physostegia virginiana L. 'Summer Snow' and 'Vivid'. Our experiments suggest that P. virginiana is a quantitative long-day plant. To ensure vegetative meristems, stock plants must be held under short days. After rooting, newly potted cuttings can be moved to long days for establishment, growth, and flowering. Forcing time at 24°C day and 17°C night temperatures was 10 weeks for 'Summer Snow' and 15 weeks for 'Vivid'. Inflorescence number on both cultivars was decreased when forced at 11°C night temperature compared with 17°C.