Veggie's random garden

   

My plans to convert this netted area into a fruit cage came to an end when the snow came and demolished the netting roof and dragged most of the uprights out of the ground. Its too far gone to rebuild it so, its Plan B. 

About half of the space is a pond, the other half is floored with slices of ash tree and gravel on top of, I think, plastic. The ash slices are mossy and slippery when wet so they have to go.
The pond is lined with, would you believe, flexible pond liner. i don't want to take this out because there's all sort of rubbish underneath - kitchen worksurface, table top, polystyrene, duvets - in fact anything I could find to  level the bottom and protect the liner from tree roots and rocks. 
My vague plan is to empty the pond, puncture the liner so that it can drain, throw the ash slices into the empty pond and try to find some soil to fill the hole with.

My question to the panel is - what plants would enjoy having their roots in this sort of location. I imagine it will stay damp and the wood will act like a sunken hugelkultur bed.