Hi,
I have a garden bed under arborvitae with the same problem, i.e. feeder roots. As in your garden, the roots have strangled hostas, heuchera, astilbe. I'll offer what does thrive: lenten roses - beautiful in winter, lilies of the valley, and, so far, sedge grass. I grew lamium for a while, but it seemed bugs or some other pest chewed the leaves. I would be interested if you've found other solutions to the feeder root problem, other plants that worked?
L Chip
