Ideally you should use about 10-15cm of fertilizer / sand mix and hold the
lot down with 4cm of gravel, 2mm diameter.

You mean mm, not cm.

--
Victor M. Martinez | The University of Texas at Austin
| Department of Chemical Engineering
http://www.che.utexas.edu/~martiv | Austin, TX 78712
If we knew what we were doing it would not be called research, would it?