4 Corners Organics Pumice - Medium (1/4" - 3/8")Pumice is formed from volcanic activity and owes it's unique porous structure to the rapid temperature and pressure changes that occur during a volcanic eruption. An excellent soil additive for increasing drainage and aeration, pumice also has a mineral content that is beneficial to plants. Pumice also assists in promoting microbial establishment and growth due to its porous nature. All of the surface area provides living environments for root zone