Hi, the outside of school program that I'm working with is starting a school garden in the patch of what appears to be grass next to the school. When I dug down to get some soil samples for testing I found that below the thin grass cover, there's a few inches thick layer of soil. We really want to get this garden up and running, does anyone have any suggestions for turning it into a usable food growing garden? Would we have to bulldoze off that layer of gravel? Would it work to rototill and mulch it? Must we build raised beds? Thank you!!