A plant growing device (2, 3) includes an envelope (21,31) and a plant growing medium (22). The envelope (21,31) is made of a sheet material and has substantially planar first and second walls (211,311,231,331), a surrounding wall (210,310) connected between the first and second walls (211,311,231,331), and a plurality of openings (232,332) formed in the second wall (231,331) and adapted to permit extension of plants (9). The plant growing medium (22) is enclosed by the envelope (21,31), and includes a water-absorptive material selected from a polymeric foam, saw dust, charcoal, soil, sand, wood pulp, polymeric fibrous substances, and natural fiber materials.
