Macro photograph of expanded clay aggregate used for hydroponic (soilless) gardening. The largest is 1 cm in diameter. Expanded clay aggregate is a lightweight ceramic manufactured in a rotating kiln. This material has a very high surface area due to all the holes and cracks. It is able to collect hydroponic chemicals and air to nurture the roots of a plant, making it an excellent delivery method for nutrients. Plants can grow at maximum rates using expanded clay aggregate. A typical hydroponic system will wet the aggregate several times a day.