Lava rock is a type of volcanic rock that is very lightweight and has excellent drainage properties. It is also very inert, so it will not affect the pH of your soil mix. Lava rock is widely used for bonsai, succulents, and other ornamental plants for its benefits as a soil conditioner. It helps to improve soil structure, drainage, airflow, and moisture retention. Lava rock can also be used as a decorative element for your bonsai pots or trays.