Charcoal can be bused to sweeten soil or water (aquariums). It is invaluable for drainage in the bottom of pots, and as an additive to home made soils.
Excellent for the bottom of non draining planters like tearrariums. It prevents the potting from becoming sour.
Good growth can be achieved by mixing 40% charcoal with 60% pine bark for Cattleya and Dendrobium orchids.