Oh wait, that's a different kind of tree ring.
I have a Sweetgum tree that the roots grow along the ground. It had a small, round, concrete ring when we bought house. Always looked like crap (tuned it twice). So time to do something different.
Had some old plastic border laying around.
Dug it in, added dirt and 4 Mirage Hot Pink Autumn Sage plants.
Not 100% satisfied, but much better than before. Think I'll like it more when plants mature