Actually I think it is there for the sprinklers to keep the foundation from cracking...
It had grass in it and annoyed me every day looking at it.
Soil is clay, I'm thinking of use small stones/gravel for the "mulch", soil is clay. It gets full sun for quite a good time. We're in Texas so gets super hot in summer and not too cold over winter. I can look up any suggestions of plants for the planting zones here.
It's about 27ft long and 1ft at widest part, tapering to uselessness.
I'm stumped!