- Ideal for propagating and growing orchids. - Growing orchids is as much an art form as it is a science. Our Whitney Farms Medium Grade Orchid Bark is sized to be an all-purpose orchid bard. It is made of a double-screened fir bark and is sized between 1/2 and 1 inch. Medium Grade Orchid Bark is alos ideal for use as a decorative topdress. - 8 dry quarts (8.8 liters).