The tree is in my flagstone courtyard. There are river stones laid underneath by a previous owner. At one point a climbing hydrangea and ivy covered them, but I needed to control them so they are no longer there. It's hard enough to weed the flagstones (I have had luck with moss and am trying creeping phlox and sedum between them), but these stones are impossible. What are my options, and their relative merits? It is not completely shady as the tree only weeps on the western side, admitting some morning sun.. Thanks for all ideas!