Irrigation insert for Coubi DUK and Coubi DUW pots, available in 4 sizes. By using Coubi systems, hydroponic cultivation is possible. In this type of cultivation, the roots of the plant are placed in an inner vessel filled with an inert substrate (e.g. expanded clay). This vessel, together with an indicator showing the optimum water level, is placed in an outer vessel, which is filled with nutrient-laden water. This method is most suitable for moisture-loving plants, but can be used to grow all houseplants, even succulents.