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 and Vanda type Orchids and other tropical plants. The fine-size bark is good for delicate seedlings, mericlones or other mature plants with fine roots.