If you are planning on leaving it on the ground and not move it, full soil would be fine. Like pinksand said, if you plan on a lot of plants they will need all they can get.
The half and half mix is really only necessary if you plan on a hanging window box where it would be suspended in the air. That's when weight becomes a concern.
"If you enjoy the fragrance of a rose, you must accept the thorns which it bears."