maytens trees

HELP! A landscaper planted a Maytens tree at the edge of one of my flower beds 15 years ago, and now the bed is so full of tiny rootsthat no other plants can compete with them! It is a sun/shade situation, and I have tried Abutilon, princess flower, Japanese anenome, Huchera, etc. etc., and nothing survives for long.

I read that if you disturb the roots, they will send up suckers -- I was planning to deeply cultivate the area and fill with amendment -- but if that will send up suckers, doesn't sound like a good fix.

Any ideas/experience out there???