A building block (1, 1A, 1B) and a wall for a building (41), assembled from a plurality of such building blocks, arranged in layers. Each building block (1, 1A, 1B) has a substantially rectangular shape and defines six, pairwise parallel, outer surfaces. The building block (1, 1A, 1B) is provided with a bottom (3, 3A, 3B), a rear wall (5, 5A, 5B), a front wall (7, 7A, 7B), a first sidewall (9, 9A, 9B) and a second sidewall (11, 11A, 11B). These walls jointly bound an internal hollow space(15, 17； 15A, 17A； 15B, 17B), which is suitable for receiving a rooting material and planting. The front wall (7, 7A, 7B) is at least partially lower than the rear wall (5, 5A, 5B). An irrigation conduit is optionally included in the assembled wall (41) within recesses (27, 29, 31； 27A, 29A, 31A； 27B, 29B, 31B) in the building blocks (1, 1A, 1B) and at least in a number of building blocks rooting material is arranged with a planting cooperating therewith.
