array9

Are they just massively lacking humus?  The history is basically one on tarmac and concrete.  Any soil there is post dam, and probably largely came with the odd low leafy shrubs that were off the shelf purchases.

I suspect the water is quick absorbed and drained, in part to avoid the weight of the water pushing the dam down or over.  Certainly nothing seems to thrive, despite lots of loving care.  

I wonder if there are any earth worms in the plot.  I don't remember ever seeing any castes.  I will have a look.  I might introduce somethings at the bottom.

M