Abstract: A growth medium consisting of a bag (1) containing a growth substrate (10). The bag (1) includes a bottom wall (11) made of an air and water-permeable material for retaining the growth substrate (10) during handling and transport. The upper wall (12) is secured to the bottom wall (11) around the edge (2) of the bag and consists of at least two superimposed sheets including a first sheet (13) made of a coarse mesh material enabling a decorative layer arranged on the medium at a later stage to be firmly attached thereto, and a second sheet (14) made of a material that is rapidly biodegradable on exposure to water and can temporarily retain the growth substrate (10) during handling and transport. A prefabricated modular medium with good decorative sheet retaining properties may thus be achieved.