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Lowland gravel, or fired clay pellets, are used in plant production in several ways. Adding a few centimetres of clay granules to the bottom of the pot and topping with soil will ensure better drainage. As a stand-alone substrate, light gravel is used in hydroponics and aquaponics where plants drive their roots into the clay pellets which provide them with the moisture, nutrients and oxygen they need to survive, resulting in more lush plant growth. .