The 2011 ASHS Annual Conference

Sphagnum moss is widely used as a substrate for the commercial cultivation of Phalaenopsis in Asia. Drop in pH of the sphagnum moss substrate during Phalaenopsis cultivation has been reported in many studies, but the causes of this phenomenon remained unclear. In this study we investigated the possible factors that would lead to the sphagnum moss substrate acidification during the cultivation of Phalaenopsis. Fertilization resulted in lower initial pH (pH measured by the pour-through technique at the first fertigation) of the substrate. Regardless of fertilization, the pH of the sphagnum moss substrate without Phalaenopsis plant increased over time, while a decrease in pH was observed in the sphagnum moss substrate having a Phalaenopsis plant in it. The effect of substrate characteristics on pH was also studied by growing Phalaenopsis plants in sphagnum moss, artificial textile fiber or pine bark. Artificial textile fiber had the highest initial pH, followed by pine bark and sphagnum moss, but acidification was observed in all substrates with increasing time in cultivation. Growth of algae on sphagnum moss was found not to be a contributing factor in the pH change of the sphagnum moss substrate, because the acidification of the moss was not affected by the exposure to or blockage from light. Therefore, the roots of Phalaenopsis plants are the primary factor contributing to the acidification of the sphagnum moss substrate.