A plant culture module for erecting a modular structure for a green wall, said module comprising: - a rack provided to internally receive a substrate of plant culture; and - at least two retaining walls (41, 42), 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; 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 (20, 21) being connected by two upper cross members and two lower cross members (22, 23) delimiting with said frames (20, 21) a lower face, an upper face and lateral faces, said upper and lower cross members (22, 23) extending between the respective ends of the upper beams (201, 211) and the lower beams (202, 212) respectively; - each retaining wall (41; 42) has first and second edges called opposite longitudinal edges and has a width taken between its first and second longitudinal edges which is lower than the distance between said frames (20, 21); - at least one of the retaining walls (41, 42) has a first longitudinal edge mounted on one of the frames (20, 21) 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 (41, 42) are both offset according to a vertical direction orthogonal to the lower and upper faces (33, 32) and according to a transverse direction orthogonal to the front and rear faces (30, 31). - a rack provided to internally receive a substrate of plant culture; and - at least two retaining walls (41, 42), 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; - 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 (20, 21) being connected by two upper cross members and two lower cross members (22, 23) delimiting with said frames (20, 21) a lower face, an upper face and lateral faces, said upper and lower cross members (22, 23) extending between the respective ends of the upper beams (201, 211) and the lower beams (202, 212) respectively; - each retaining wall (41; 42) has first and second edges called opposite longitudinal edges and has a width taken between its first and second longitudinal edges which is lower than the distance between said frames (20, 21); - at least one of the retaining walls (41, 42) has a first longitudinal edge mounted on one of the frames (20, 21) 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 (41, 42) are both offset according to a vertical direction orthogonal to the lower and upper faces (33, 32) and according to a transverse direction orthogonal to the front and rear faces (30, 31).