Harris Orchid Potting Soil contains heat treated Douglas fir bark, peat moss, pumice and perlite in an optimal ratio that is ideal for use with a variety of orchids, including Phalaenopsis, Cattleyas, Dendrobiums, Cymbidiums, Oncidiums, and all epiphytic orchids. Most orchids have roots that need more air space and better drainage than potting soil alone can provide. Orchids should have potting material that drains rapidly and at the same time retains moisture. for best results, repot orchids every 1-2 years.