Abstract

Seeds of Rhododendron carolinianum Rehd. (Carolina rhododendron) were germinated at 25°C (77°F) or an 8/16 hr thermoperiod of 25°/15°C (77°/59°F) with daily photoperiods of 0, 1/2, 1/2 twice daily, 1, 2, 4, 8, 12, or 24 hr. For both temperatures, no germination occurred during a 30-day period for seeds not subjected to light. At 25°C (77°F) increasing photoperiods increased germination with germination of 26 and 39% occurring by day 30 for the 12 and 24 hr photoperiods, respectively. The alternating temperature of 25°/15°C (77°/59°F) enhanced germination when light was limiting. At this temperature germination ≥58%occurred by day 30 for photoperiods ≥4 hr. For photoperiods ≥8 hr, 30-day germination ≥70% was realized.