You can also use this technique with paper junk mail such as catalogs, news paper, magazines and paper grocery bags. Since paper is already thin it is really easy to turn the resulting charcoal into fine pieces with lots of surface area.

I recently upgraded to a 4ft deep trench. A lot less work cutting materials to fit, but I do get some dirt in the charcoal and lose a bunch of charcoal into the dirt.

First ingredient is rape