Effect of Plant Hormone on Foxtail Orchid Using Different Substrates

The Foxtail orchid (Rhynchostylis retusa L.) is an attractive and valuable ornamental flowering plant distributed in South-east Asia. It is popular for its beauty and medicinal value. The aim of this study was to assess the effects of various growth substrates and plant hormone (Indole-3-Acetic Acid, IAA) on the growth of Foxtail orchid. A pot experiment was conducted under net house condition at Sylhet Agricultural University during 8th March 2025 to 22nd October 2025. Three growing substrates (coconut husk, tree bark and sawdust) and four different concentrations of IAA (0, 2, 4, and 6 ppm) were used. The treatments were arranged in a completely randomized design (CRD) with three replications. IAA was applied through spray to the leaves, roots, and growing substrates at 15 days intervals. Data were recorded at15 days intervals up to 225 days after establishment of the plants. The result showed that both substrates and IAA concentration significantly influenced the growth of Foxtail orchid. Among the substrates, plants grown on sawdust had the highest number of leaves (8.08) and the longest leaf length (9.72 cm) compared with coconut husk and tree bark substrates.