Effect of Fall Temperature and Lighting on Growth of Rhododendron Rooted Cuttings

Summer-rooted rhododendron cuttings were forced into growth using natural photoperiod, incandescent or red light (660nm) as a night break between 2200 and 0100 hours at both 17°C (63°F) and 10°C (50°F) minimum night temperature (MNT) for 3 weeks beginning September 28, 1982. Longer shoots were produced on Rhododendron ‘PJM hybrids’ under incandescent light than under red light or natural photoperiod. Rhododendron ‘Roseum Elegans’ produced longer shoots under both light regimes than under natural photoperiod and longer shoots at 17°C (63°F) MNT than at 10°C (50°F) MNT. Neither temperature nor light treatments significantly increased the average number of breaks per plant of either cultivar. Spring growth of Rhododendron ‘Roseum Elegans’ was delayed by both red and incandescent fall light treatments, but not by the high temperature fall treatment.