Expanded clay is produced by heating high-quality natural clay with expansion additives in a rotating kiln to 850 and 1,200 °C. This treatment causes the clay granule volume to expand to a multiple of its original size. Originally, expanded clay granules were feedstock used in the construction industry. Due to their special properties, expanded clay granules are now used in numerous applications in gardening and landscaping. A special extraction method and testing schedule for expanded clay granules (developed at the Institut für Bodenkunde und Pflanzenernährung [Institute of Horticulture] at Hochschule Weihenstephan-Triesdorf) ensure that plants tolerate the material.