One-year-old corms of Liatris spicata Willd. produced from seed and 2-year-old corms from division of previously forced corms were placed under 8 hours of natural daylight plus 0, 4, 6, or 8 hours of incandescent (5 μmol·s-l·m-2) day continuation to equal 8-, 12-, or 16-hour photoperiods. Plants were grown under these photoperiods during the first 35 days after shoot emergence (initial) and then were grown under a second photoperiod of 8, 12, 14, or 16 hours until harvest (final). The combination of initial and final photoperiod treatments resulted in a total of 16 photoperiod combinations. Two-year-old corms flowered 10 days earlier than l-year-old corms, but l-year-old corms produced twice as many vegetative shoots and 15% more flowering shoots than the 2-year-old corms. Long initial photoperiod (14 or 16 hours) treatments. (LD) reduced-the days to flower by 8 days and increased flower shoot elongation by 20 cm, compared with initial short days (8 or 12 hours, SD). However, initial LD treatments decreased the number of flowering shoots by 50%, compared to initial SD treatments. An initial SD followed by a final LD did not decrease the number of flowering shoots, yet promoted greater stem elongation (92 cm) than continuous LD (83 cm).
Shoot emergence of cold-treated Liatris spicata Willd. corms was inhibited by SC soil, delayed at 10 or 15C (7 and 5 days, respectively), and promoted at 20, 25, or 30C. Within 15 days after planting, soil at 20C promoted the highest percentage of shoot emergence (81%). Plants were grown during the first 35 days after emergence under a combination of temperature and long or short days. Flowering shoot length was increased by either short days (8 hours; SD) at 13 or 15C or a 4-hour incandescent night interruption (NI) at 18C. When planted in May, a NI at 15 or 18C decreased the time to harvest by up to 14 days, whereas in November increasing the temperature to 18C, regardless of photoperiod, decreased the days to harvest by 16 days. Plants grown during the first 35 days after emergence under natural days at 15C then placed at 13, 15, or 18C under NI until harvest did not respond to the increasing temperature. Temperature and photoperiod influence Liatris development primarily during the first 35 days of development.