2017 ASHS Annual Conference

Phalaenopsis (Phalaenopsis spp.) is now the most important indoor potted plant worldwide. Results in the literature regarding whether growers can delay or advance its spiking by high or low nitrogen (N) level, respectively, have been controversial. The aim of this study is thus to investigate how short-term N application or starving affect tissue carbon-nitrogen (C:N) ratio and flowering of phalaenopsis. Nutrient solutions with four N levels, namely, high (28.6 mM N), normal (14.3 mM N), low (1.43 mM N), and deficient (0 mM N), were applied to two phalaenopsis cultivars in their last 8 weeks of vegetative growth at 30/28˚C and the same fertilization regimen was carried onto their reproductive growth stage at 20/18˚C. A significant difference of tissue N concentration is detected in both cultivars 8 weeks after treatment: Higher N level in nutrient solution resulted in higher tissue N concentration and lower C:N ratio. The roots and shoot both had a negative N gain in the low N and deficient N treatments during the reproductive stage of the two cultivars, indicating that stored N was utilized for inflorescences development when N supply was limited. All plants spiked and flowered but differed slightly in time and quality of flowering. High N delayed the spiking of the small, purple-flowered phalaenopsis (Phal. Sogo Lotte ‘F2510’) by 8.9 days but did not affect the large, white-flowered phalaenopsis (Phal. Sogo Yukidian ‘V3’). Plants in low N and deficient N treatments spiked only 1-2 days earlier than the normal N treatment in both cultivars. Nitrogen levels did not affect flower count of the large-flowered ‘V3’ but number of flowers in the small-flowered ‘F2510’ was reduced by 2 and 3 in the low N and deficient N treatments, respectively. The longevities of the first flower and whole inflorescence were not affected by N levels in both cultivars. It is concluded that effects of short-term N application on spiking and flowering of phalaenopsis mainly depend on the size of stored N pool, such that flowering performance of miniature-type phalaenopsis is more likely to be lightly manipulated by short-term N application but not those of standard-type phalaenopsis.