So, on my way to a meeting, I found this. It's here. You can actually have quite a good look at in on Google Maps (that's what the link is) but I've put some of the planting detail below.
Definitely an apple tree in one of those battleship-grey dazzle angular wall planters. It's a green wall alright - and just as dependent on its irigation system, which was visible in the lower planters - but not a regular, commercial-district type green wall. This had more of an ostentatious municipal feel, the glory of dramatic urban planning sinking deep into the finer details.
The artist, Neil Ayling, does not seem to put plants in his sculptures very much. Mostly they are angular, gravity-defying collapses of cityscapes into eyebending flying structures; concrete and graffiti folded up like origami.
There must be other sculptures out there which would also make excellent planters.