Patches of Green VOLCANIC GARDEN PUMICE ROCK from 16 Dry Quarts Bag This natural volcanic rock is excellent as an all-purpose soil addition, preferred choice among many gardeners. Great amendment for all types of garden soils, potting soils, or planting mixes and perfect for use in indoor or outdoor containers, garden beds, raised beds, and hanging baskets. Pumice is more durable than perlite or vermiculite. It is rough and porous, facilitating soil aeration and providing more room for roots to grow. It is lightweight and small pieces can float in water. Pumice absorbs water and assists in keeping soil moist. Screened to 3/8". This means 3/8" and smaller. Product is mined, screened, stored outdoors in large quantities causing batches to vary in dryness / dampness. Larger pieces may be mixed in.