Patches of Green BONSAI & SUCCULENT GARDEN PUMICE ROCK is an excellent, all-purpose soil addition. Pumice is a natural volcanic rock, perfect for use in all indoor and outdoor gardens. It is lightweight, porous, natural, and durable, and useable in all types of garden soils, potting soils, or planting mixes and for use in indoor or outdoor containers, garden beds, raised beds, and hanging baskets. It is stored outdoors, near other soil amendments and landscaping materials.