A plant culture module for erecting a modular structure for a green wall, said module comprising: - a rack provided to internally receive a substrate (SU) of plant culture; and - at least two retaining walls , where each retaining wall (41; 42) is permeable, in particular by being of the grid, porous or perforated wall type, and is carried by the rack to form a shelf for retaining the substrate (SU); said module being characterized in that : - the rack has a front frame and a rear frame facing each other and delimiting respectively a front face and a rear face , where the front frame and the rear frame each have respectively two lower (202; 212) and upper (201; 211) beams, connected by two opposite lateral uprights (203; 213), said frames being connected by two upper cross members and two lower cross members delimiting with said frames a lower face , an upper face and lateral faces , said upper and lower cross members extending between the respective ends of the upper beams and the lower beams respectively; - each retaining wall (41; 42) has first and second edges called opposite longitudinal edges and has a width (LP) taken between its first and second longitudinal edges which is lower than the distance (LA) between said frames ; - at least one of the retaining walls has a first longitudinal edge mounted on one of the frames and a second free longitudinal edge, so that said retaining wall (41; 42) extends from one of the frames (20; 21) without reaching the other frame (21; 20); and - the two retaining walls are both offset according to a vertical direction orthogonal to the lower and upper faces and according to a transverse direction orthogonal to the front and rear faces . - a rack provided to internally receive a substrate (SU) of plant culture; and - at least two retaining walls , where each retaining wall (41; 42) is permeable, in particular by being of the grid, porous or perforated wall type, and is carried by the rack to form a shelf for retaining the substrate (SU); - the rack has a front frame and a rear frame facing each other and delimiting respectively a front face and a rear face , where the front frame and the rear frame each have respectively two lower (202; 212) and upper (201; 211) beams, connected by two opposite lateral uprights (203; 213), said frames being connected by two upper cross members and two lower cross members delimiting with said frames a lower face , an upper face and lateral faces , said upper and lower cross members extending between the respective ends of the upper beams and the lower beams respectively; - each retaining wall (41; 42) has first and second edges called opposite longitudinal edges and has a width (LP) taken between its first and second longitudinal edges which is lower than the distance (LA) between said frames ; - at least one of the retaining walls has a first longitudinal edge mounted on one of the frames and a second free longitudinal edge, so that said retaining wall (41; 42) extends from one of the frames (20; 21) without reaching the other frame (21; 20); and - the two retaining walls are both offset according to a vertical direction orthogonal to the lower and upper faces and according to a transverse direction orthogonal to the front and rear faces . <EOS>