David762
Member
Two things -- hardwood charcoal, such as "Cowboy" brand from Home Depot, and coarse perlite. Use a hammer to break the Cowboy charcoal up into pieces 1/2" or so -- save the dust to mix in the soil as well. For your 8 1.5 cubic feet of soil, I would use at least 2 bags of the hardwood charcoal, mixed 2:1 with the coarse perlite.