Nutrient Management of Potted Dendrobium and Oncidium Orchids

With the difficulty of consistently obtaining high quality peat moss due to availability and cost, an alternative potting media component would be desirable for orchid production in Hawaii. Coir fiber offers a possible low cost alternative. A study with potted dendrobium and oncidium orchids was conducted at the University of Hawaii Magoon Greenhouse Facility. The oncidium orchid was Brassia Haleahi Spider 'Golden Swords' x Brs. Caudata, and the dendrobium orchid was Dendrobium Jaquelyn Thomas (UH232) 'Uniwai Supreme'. Two potting media were used—a 3:1 (by volume) black volcanic cinder:peat moss mixture and 3:1 black volcanic cinder:coir fiber mixture. Nutricote controlled release 13N-13P-13K fertilizer was applied at two rates—0.5 g and 1.0 g per 10.2-cm pot. Oncidium orchids: with the cinder:peat moss media and the cinder:coir potting media, the higher fertilizer rate resulted in a taller plant and more leaves compared to the lower rate. With both media, the number of flowers per plant was similar for both fertilizer rates. The percentage of plants that flowered was similar for the two fertilizer rates for each media. The percentage flowering was higher with the cinder:peat moss media. Dendrobium orchids: with the cinder:peat moss media and the cinder:coir potting media, the higher fertilizer rate resulted in a taller plant and more leaves compared to the lower rate. With both media, the number of flowers per plant was similar for both fertilizer rates. For each media, the percentage of plants that flowered was higher with the higher rate of fertilizer. The percentage flowering was similar for the two media. This study has shown that coir fiber may be a suitable alternative to peat moss in a volcanic black cinder potting media for orchid production in Hawaii. Use of a lower fertilizer application rate could help reduce leaching of nutrients from the pots, minimize environmental impacts, and reduce fertilizer costs to the grower.