The Florist and Pomologist, p. 95 (1882)
Charcoal in Potting Soils

The value of Charcoal in Potting Soils, as an agent in keeping them open and porous, can hardly be too highly estimated. Such prime Auricula growers as the Rev. F. D. Horner, Mr. S. Barlow, Mr. B. Simonite, and others use it largely in their composts, and with the best effects. It is not a mere mechanical agent like sand, but an active principle, having, as Liebig remarks, "a physical as well as a chemical effect on soils decidedly useful. It renders them, as far as it is present, light and friable, and gives additional warmth to them by its colour, which absorbs and retains readily the rays of the sun during the day; wherever charcoal has been applied rust never affects the growth of Wheat." Those who use charcoal in Auricula soils find less losses among their plants than when sand is employed to give it a porous character, and the roots ramify more freely in it. The cost of charcoal as compared with sand is much heavier, but its operation is so beneficial as to compensate in a great degree for its extra cost. Then there is the labour of breaking it up small enough for potting purposes; if it could be bought reduced to finer particles it would be advantageous, and perhaps this boon will be allowed should the demand for it materially increase.(Gard, Chron., N.S., xvii, 437.)