The principle is simple. Rather than having a hole in the bottom of the pot, there is instead a reservoir of water. Potting soil is suspended above the water reservoir by means of a perforated barrier. Circular “wicking chambers” reach down into the reservoir and draw water up to the plant’s roots. The reservoir is refilled by means of a pipe that comes out of the top of the pot and the soil in the pot is covered with a layer of plastic that acts as mulch. Depending on how deep the water reservoir is, it’s possible to go many days without having to add water. This arrangement, combined with the mulch layer on top prevent wasteful over-watering that can occur with conventional pots.