dirty hands
Full Access Member
I would reuse the slate after removing it and freshening the area above the border to prevent weeds. The lower area i wouldnt put the slate in but i would use black mulch instead.
The lower area I would plant rhubarb hostas ligularia and or astilbe. I like large leaf plants.

Above maybe hakone. I think it would look good and stay compact so it wouldn't grow above the porch or windows. It looks good in pots too.

It would also brighten the area a little drawing your eye to the other plants.

