My large front "lawn" lies over the septic field and gets sun all day. It is a horrible collection of very little real grass presently, lots of clover, moss, and random volunteer plants like Queen Anne's Lace, daisies and other weeds. It's a mess and the soil is not great. While I love the look of a smooth lawn that sets off the flower beds that ring this area, as a picture frame sets off artwork, I have given up on the idea of a decent lawn here. That's okay. What I want to know is this:

Is it appropriate to make some raised flower (not food crops) beds here with board-type edging and create a more attractive aspect? I would research and avoid plants with long tap-roots. I am concerned with interfering with the septic field and don't want to compromise its functioning. But would 8-12" raised beds be okay here?? I am in despair and want to improve this area without trying to do a complete lawn makeover (been there, done that, and failure was the result).

Any advice?