Pumice is a relatively light weight volcanic, porous, stone material that is popular on the west coast to provide aeration to soil mixes. Because it is a stone material, it does not break down in the soil. Its porous nature allows it to suck up and hold onto moisture, while permitting excess water to flow through the mix easily.
It is primarily used for its ability to amend and improve garden soil by providing improved aeration and moisture retention. Pumice is solidified foam that forms from lava rich in gases. It has an intricate network of cavities that creates structure that is 70% porous and absorbs moisture well. The porous structure of pumice gives it some unique qualities making it useful for gardening. It has a low bulk density and is neutrally buoyant meaning it won’t sink to the bottom of the soil or float to the top. Horticultural grade lightweight Pumice is inorganic so it has no odor and won’t break down, decompose, shrink, compact, or rot. Added to garden soil, it will improve the soil making it more porous and improving aeration and drainage while maintaining a reduced soil weight.