For forming a water-retaining layer at the bottom of a houseplant pot so that the plant present in the houseplant pot needs watering, less frequently, a pad 11 comprising a root permeable separation sheet 13 having swellable gel pellets 15 attached to one side and evenly spread over this side, is placed on the bottom of a houseplant pot with the root-permeable separation sheet turned upwards. Subsequently, soil is added to the pad in the houseplant pot after which water is added so as to make the gel pellets swell. During a watering, operation the water is absorbed and retained by the gel layer. After this the plant can be potted in the soil. The roots of the plant will grow into the gel layer at the bottom of the houseplant pot and extract water from the gel layer for a long period of time, so that watering needs to take place less frequently.
