I have completed the 5th course of the retaining wall and will be placing the final 6th course. This will be a large planting bed so I have a question. What should be my final layers? The block is 8" and the cap is 4" So far will be planting, bulbs, small shrubs and other perennials. "Brown Plus" or soil with compost mixed in is $16 a cubic yard cheaper than topsoil and $20 a cubic yard cheaper than organic topsoil. I will need about 16 cubic yards to fill the bed to the top. I have plenty of backfill soil I removed that I can replace. What should be depth of final topsoil? I had planned on placing the geo-grid that is due with this course and about 4" of the backfill soil, leaving 8" remaining is that going to be too much or too little topsoil?