WHY CHOOSE US? ZeeDix Clay Pebbles are made of natural clay. Non-toxic, color won't fade away through time. This natural clay is mined, formed into pellets, then kiln fired at high temperatures to cause the clay to expand into tough, lightweight balls. Clay naturally has balanced capillary action,with an ideal surface structure.The length of the gardening orchid hydroponic grow media pebbles is 4mm-16mm, reddish-brown in color and mostly round in shape, used as a decorative top layer for indoor plants and outdoor gardens and also to prevent rapid drying of topsoil.Top dressing for more finished look.Top dressing to stable plants,keep the soil form shifting around,Mixed with soil mix to help plants breath,Mixed with soil mix to improve drainge.Add as buttom pad in pots to help extra water flow out.