DESCRIPTION Pumice ( filtered 3/8" to 1/4" in size ) is relatively lightweight volcanic rock used as an amendment in all types of soil. Its porous composition allows it to retain moisture and nutrients during watering, and release them slowly over time as the root system requires. Think of these components as little batteries for your plants! We dry our material before packing to make for a more satisfying, so it won't be damp, nasty, and full of fines/powder like most pumice options out there. :)