Substrates Affect Irrigation Frequency and Plant Growth of Potted Orchid

Production efficiency is an integral part of potted orchid production.  Proper selection of substrate is essential because it affects the amount of water and fertilizer application, disease incidence, plant growth and production cost, and ultimately determines farm income. The purpose of this study was to determine the best bark-based medium for orchid production.  Physical properties were assessed by measuring distribution of air, water and solid space in an 8.89-cm-square pot for redwood bark, volcanic cinder, coir croutons, oasis hortcube, Pindstrup peat, sphagnum and rock wool. Sphagnum, peat and coir croutons were observed to have the highest water retention; these 3 media were then individually mixed with bark and physical properties of the mix were assessed. Sphagnum moss provided the largest increase in water space with minimum loss of air space when mixed with bark. Orchid  Miltassa Shelob ‘Tolkien’ were therefore grown in bark:sphagnum  media in a mixing ratio of 100:0, 75:25, 50:50, 25:75 or 0:100 by volume, and fertigated at a various irrigation frequency. There was an interaction between medium water retention capacity and fertigation frequency on the growth of potted orchids after 9 months. Higher sphagnum ratio in the media increased water retention capacity and subsequently enhanced plant growth when fertigation frequency was 1x, 2x, or 3x a week.  However, at higher fertigation frequencies, media composition and water holding capacity had little effect on orchid growth. Our results confirm that the composition of potting substrates is important for determining the irrigation frequency and plant growth in orchid production.