It comprises an outer pot having an inner cavity for receiving an inner pot, the outer pot having an interior where a tray structure is provided comprising trays dividing said interior into sub-chambers arranged at different levels for supplying watering liquid towards the inner cavity at different heights through openings formed in the outer and inner pots. Valve means operated according to the hydrostatic pressure of the watering liquid in the sub-chamber are provided for allowing controlled supply of watering liquid to the inner cavity. Adjusting means are provided for controlling the amount of watering liquid supplied into each sub-chamber.
