The apparatus has the housing (1) which is divided to a main chamber (2) and a side chamber (3). The main chamber and the side chamber are connected with each other and are made to open upwardly. The main chamber is provided with a receiving opening (16) for receiving a plant pot. The side wall (4) in the side chamber is made lower than the side wall of the main chamber. A lid (5) is provided to cover the lateral space of the housing, and is provided with the opening (6) from which a filling level indicator (7) is protruded.
