Premier PRO-MIX® BRK20 BIOFUNGICIDE™ + MYCORRHIZAE™ 60cu ft - Loose Fill Tote Formulated with an aged pine bark, pro-mix bark is nitrogen stabilized & therefore well suited for growers who require more frequent dry down periods & have to compose with a changing growing environment. PRO-MIX bark is a carefully design low water retention growing medium which will provide quality & consistency for great results.