Living Walls

The completion of London's biggest living wall was recently announced.  The publicity surrounding such projects is often about how "green" and sustainable they are, but I do wonder how true this is.  Moving a large amount of soil in and putting it in a vertical framework, presumably with some sort of artificial irrigation system does not strike me as an especially sustainable approach.  I am sure it must reduce surface water flooding in the immediate area, but it seems an immensely elaborate way to do so.