Pumice is a porous volcanic glass formed from the rapidly cooled froth of lava flows. As a soil amendment pumice is lauded for its dual use application for aeration to allow water drainage and increase oxygen flow, and its porosity allows for the storage of water and nutrients- making them available to roots as the plant needs. In potting soil, pumice is the perfect substitute for perlite- pumice is a little heavier than perlite which prevents it from ‘floating’ to the surface like perlite will. Pumice is often used as a base for succulents and desert plants because it creates a well-draining environment for plants that thrive in arid and drought like conditions.
Mix as much as 33% pumice to compacted soil or potting mixes for increased aeration. For cactus and desert adapted landscapes lay a 4-6 inch bed of pumice beneath transplants, thicker applications in clay heavy soils. For soil-less growing practices mix up to 40% pumice with preferred growing medium.