The Douglas Fir Bark Dust helps to heal the newly cut seed potato surface. The healed potatoes do not shrink and curl, and the slightly acidic bark serves as a natural fungicide. Resins and waxes in the Douglas fir bark also help by reducing the moisture buildup process on the cut seed. Apply the dust to the cut seed. After treating the potatoes, store them for a minimum of 24 hours. The treated potatoes may be held up to one week.