Effects of darkness on stem elongation in tulip

Effects of darkness during the growing-period on the internode elongation of tulips were investigated. The last internode was the longest one when grown under natural light conditions, while continuous darkness caused the first internode to elongate the most. Application of a 5-day dark treatment to growing tulips during the phase of rapid stem extension resulted in significant increase in the length of the first internode. It was effective in obtaining taller tulips owing to increased elongation of the first internode, and may be effectively applied to tulip cut-flower production.