Leca is an acronym for lightweight expanded clay aggregate. When you use Leca, you can create a false bottom and raise your plants roots from the bottom of the pot. You then add water until its just touching the roots and the clay balls will start to soak up the water in the pot whilst keeping the plant away from the water. This is fantastic for plants that are prone to root rot. Leca is also used for propagating cuttings. It is a fantastic medium for a fresh cuttings because it allows air flow and helps prevent rot. It is also very easy to use and maintain. The water in Leca needs replacing ideally once a week, and it needs cleaning (boiled for 10 minutes) once a month.