Orchid Potting Mix - Fine Orchid Bark with Charcoal & Sponge Rock. 1/4 Cubic Foot Bag. Mix of Fine orchid fir bark with generous portions of both Charcoal and Sponge Rock Custom blended by Jims Orchid Supplies. If you are not purchasing from Jims Orchid Supplies you are not getting Jims custom blend. Developed 20 years ago. Popular all around general purpose orchid potting medium. We recommend soaking mix before repotting. Will store for years if put away dry. Rexius brand douglas fir orchid grade, dried and heat treared bark Jim's orchid supplies offers a wide variety of orchid growing supplies including quality orchid potting mediums: