Horticulture

I finally managed to work out what was going on with feature (111) today; one of those revelatory moments when you feel a complete idiot for not having seen it before.
D'oh!
I realise I was probably standing in exactly the same place as yesterday for this blip. Oh, well. We've all done it.
These trenches were filled with, well, basically builders' rubble. Half bricks and roof tiles and loads of mortar and plaster. Obviously planting lime-loving plants that like really good drainage. Any ideas for candidates?