An expandable plant growth system by which different varieties of plants and plant clones can be grown indoors with neither seeds nor soil. The plant growth system includes a plurality of tiers that are stacked one above the other. Each tier includes a water support tray that surrounds a hollow plant support frame. A root irrigation channel runs around each of the water support trays. Water is pumped from a reservoir to the root irrigation channels around the water support trays. The plant support frame retains the plants such that the roots thereof are held within the root irrigation channels to receive water and nutrients therefrom. Water is returned to the reservoir under the influence of gravity by a series of water transfer tubes which connect the root irrigation channels to each other and to the reservoir.
