Patches of Green Garden Pumice Rock is an excellent, all-purpose soil addition for all of your gardening needs. Pumice is a natural volcanic rock, perfect for use in all indoor and outdoor gardens. It is lightweight, porous, natural, and durable. Pumice stone is the finest choice for adding to all types of garden soils, potting soils, or planting mixes. Patches of Green Garden volcanic pumice rock for plants is a favorite among gardeners for use in indoor or outdoor containers, garden beds, raised beds, and hanging baskets.