2017 ASHS Annual Conference

Dendrobium orchids have a sympodial growth form with new pseudobulbs arising from the rhizome at the base of the previous pseudobulb. In the University of Hawaii cut flower dendrobiums the new pseudobulbs begin growth in March to June with inflorescences flowering from the top 3-4 nodes in September to December. The pseudobulb remains dormant until March to June, when new inflorescences develop from the next 3-4 nodes down from the top, and flower in June to August. New pseudobulbs also begin growth March to June with flowering from September to December. Each pseudobulb usually produces at least 3 years of inflorescences with the last year producing shorter inflorescences on leafless pseudobulbs. A 10-ml drench of 500 ppm 6-benzylaminopurine (BA) to rhizome and roots at the base of the latest pseudobulb, in early July results in new pseudobulb growth and cut flower spray production 5 to 5-1/2 months later in early December. Treatment to part of the crop every 2 weeks from September through December could result in spray production from February through May. A 450 ppm BA spray applied to the upper leaves of mature pseudobulbs of potted dendrobiums produced more sprays per pseudobulb (1.2 vs 0.7 for control), more flowers/spray (15.5 vs 9.5) and more total flowers per 9 pseudobulbs (170 vs 57). To develop a more uniform crop, mature and immature pseudo bulbs can be treated with transcinnamic acid (TCA) along with the BA to stop pseudobulb growth so the BA will be more effective. A 1 ml spray of 30mg/l TCA to the tip of immature pseudobulbs resulted in 9 of 9 flowering vs 3 of 9 for controls. Treatment with 450 B concurrent with the TCA treatment resulted in 1.33 sprays per pseudobulb vs 0.33 for untreated controls and 18.83 flowers per spray vs 11.00.