How much topsoil to grow grass
I want to extend my backyard out a little. I have a french drain that is covered in crush stone that currently marks the perimeter of my lawn right now. I want to excavate some of the stone, put down some landscape fabric, and then put topsoil on top and plant more grass so it's level with the rest of my yard. The other option is going over the top with soil where it is now but that would take up a lot more, be more work, and change the entire grade of my backyard.
How thick does the topsoil layer have to be? I think I might be able to get 6" of topsoil there right now. Is 6" enough for grass to grow?