This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Elaborate composts are not required, and one that is open and free will root and grow the young plants well. Old potting soil, with the addition of spent mushroom bed makes a good mixture. Some growers root their cuttings in "stores", either in boxes or pots, to economize room; but rooting singly in thumb pots is certainty preferable, because it does away with the second handling, an important item in most places. The cuttings can be taken when they are 3-4 in. high, and in the same way as in the case of Fuchsias or Heliotropes. Do not take them with a heel, or the basal eyes will be destroyed. Cuttings should be inserted as expeditiously as possible, to avoid their flagging, from which they always take a long time to recover. As soon as they emit roots they should be moved into another house and placed on beds of ashes, as close to the light as possible. Finally, they can be sorted into the different sections to which they belong and put into alphabetical order; where large collections are kept this takes up an enormous amount of frame room, but it is absolutely necessary to enable one to execute orders quickly and correctly, for nowadays most orders are sent to purchaser's selection, and in these hustling times every buyer is in a hurry.