Pumice 1 cf

A porous volcanic mineral.  Much heavier than perlite and vermiculite and less prone to floating to the top of pots and containers.  Longer lasting in garden soil. 

Fine grade (~1/8") is new for 2022 as a soil-mix substitute for out-of-stock fine perlite and vermiculite.  Medium grade (~1/4") is best for propagation and larger containers.