Uni-Gro Orchid Bark is the preferred growing medium for Orchids. It is made from 100% Fir Bark - uniform in size and free from dust and splinters. The medium-size bark is good for blooming Cattleyas, Phalaenopsis, Vanda-type Orchids, and other tropical plants. The fine-size bark is good for delicate seedlings, mericlones, or other mature plants with fine roots.