Pumice is a lightweight, volcanic rock that is often used in gardening to improve drainage and aeration in soils, and it can also help to control weeds. Pumice also increases soil absorption, reducing water runoff and fertilization; it absorbs excess moisture, preventing roots from drying out. And because it is a natural, unprocessed organic product it does not decompose or degrade. Pumice also can be used as a mulch to help keep roots cool in hot weather. Pre-packed from Mt. Mazama – a $50 Value!