Sulfidic waste rock from mining activity is environmentally harmful because water draining through the rock accumulates sulfuric acid, heavy metals and sulfates. This study examines the durability of a potassium permanganate protective coating (passivation) on potentially acidic waste rock for preventing acid generation. There is limited biological and physical data on the environmental impact and durability of passivation technology. The objective of this study was to measure the effect of plant roots on the stability of passivated waste rock in comparison to limed waste rock for one year. Passivation stability was determined by measuring the pH, EC and sulfate of drainage leachate and a hydrogen peroxide stability test. The experimental units were kept at field capacity and were leached once a month with RO water. Experimental units were periodically taken from the greenhouse to be tested and utilized for the stability tests. Preliminary results show a slight advantage of passivation compared to limed treatments.