Determining the nutritional requirements for optimizing flowering of the nobile dendrobium as a potted orchid

Five experiments were conducted to determine how nitrogen (N), phosphorus (P), and potassium (K) rate and fertilizer termination time, duration of N application, and cold duration and light intensity affect growth and flowering of Dendrobium nobile Red Emperor ‘Prince’. The N, P, and K experiments were a factorial combination of five nutrient rates and three termination dates (1 Sept., 1 Oct., and 1 Nov. 2005). N and K rates were 0, 50, 100, 200, and 400 mg•L-1. Phosphorus rates were 0, 25, 50, 100, and 200 mg•L-1. For all nutrients, terminating fertilization on 1 Oct. or 1 Nov. resulted in thinner pseudobulbs. Pseudobulbs grew taller as N rate increased, peaking at 100 and 200 mg•L-1. There were interactions between N rate and fertilizer termination time on all reproductive characteristics. For all fertilizer termination times, flower number increased once N was applied. When terminated on 1 Nov., 200 and 400 mg•L-1 N caused a delay for the first flower to reach anthesis. Plants required more days to full flower when supplied with 200 mg•L-1 N until 1 Oct. All P rates resulted in taller plants with equally more nodes compared to 0 mg•L-1. For all three termination times, plants that were not supplied with P bloomed later than those receiving P. Plants produced the most flowers when P fertilization was terminated on 1 Oct. Plants required fewer days to reach full flower at the 1 Sept. P termination time. As K rate increased from 0 to 100 mg•L-1, height increased, with no further increase at higher rates. Total flower number and flowering node number were the lowest at 0 mg•L-1 K. Leaf number increased as N and K rates increased up to 200 mg•L-1. Nitrogen application did not affect vegetative or flowering characteristics when one rate was applied at four termination dates. In the last experiment, plants cooled at 10 °C for 2, 4, or 6 weeks with light or 4 weeks in darkness produced similar higher number of flowers per plant than those cooled in darkness for 2 or 4 weeks or those that remained in a greenhouse