Viastone Expanded Clay Rocks, 10-Liter Viastone, an incredibly useful growing medium derived from clay. Clay itself is renewable and plentiful, making Viastone a premium growing medium due to its ecologically sustainable quality. Use Viastone virtually anywhere: the greenhouse, propagation systems, outdoor gardening, around shrubs and trees, compost aeration, rooftop gardening, house plants, hydroponic growing, etc. When estimating necessary amount of Viastone for your particular application understand that the 10 l quantity is based on the standard Horticultural trade Gal. = 0. 71 U. S. liquid gallon. PH neutral/lightweight/reusable. Please rinse packaged rocks before use due to dust or particles from shipping.