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.
For market purposes small specimens are chiefly grown in pots varying from 1¼ - 3 in.; larger specimens, if required, may usually be picked out from among the stock plants. A stock of varieties is easily raised from seed and cuttings. Both may be obtained from F. A. Haage, jun., Erfurt, Germany, or from Franz de Laet, Contich, Belgium.
If seedlings are to be raised, the best time to sow is in February, in a temperature of 65°-70° F. The soil should consist of 3 parts turfy loam, 1 part sand, and ½ part each of peat and leaf mould. Well-crocked 6-in. pots should be filled to within 1 in. of the top, scalded with boiling water, and then the seed sown thinly on top and lightly covered with soil. A sheet of glass may be used to cover the pots, or, better still, a small pit may be made for them in the house. An even temperature must be maintained, and the soil kept uniformly moist. The seeds ought to germinate in from two to four weeks, and will require pricking off', as soon as sufficiently large for handling, into 6-in. pots, using the same compost as for seeds.
The seedlings will need to be kept under glass as before until established, when they may be moved into a position where they will get more light and air; a temperature of 60° to 65° F. by day and 5 degrees less at night should be maintained. As they grow they require pricking off into boxes, the ordinary seed trays for preference, using 5 parts of soil, 1 sand, and ½ each peat and leaf mould. One or two more prickings off may be necessary, but too much root run is injurious to the young plants. Grow the plants on in boxes until ready for the various-sized pots. For potting, the last compost mentioned, but slightly rougher, will do admirably. Once potted, and the plants well established, they are ready for sale. Careful watering is necessary at all times, especially during the winter months, when very little is required. Cuttings of Cacti and Succulents need to be handled quite differently from any other cuttings. They must not be inserted in soil until absolutely dry and firm at the base. This will take from two weeks for Opuntias to four or six weeks for Cereus and Euphorbias, perhaps slightly longer in winter. They should be potted in the ordinary manner, using the same compost, which should be nearly dry. It must be kept dry until rooting commences, when water may be given very sparingly until the plants are established. A fair number of plants should be grown on to make large ones for seeds and cuttings. Most of these plants should be taken out and repotted in the early spring each year. Those varieties grown from seed should be kept in a cool airy greenhouse - facing south if possible - during the summer. To flower well the plants must be well ripened, and hand fertilization is necessary to ensure seed.
Mealy Bug is the chief pest of Cacti, but this may be kept down by the usual methods. Sun-scald sometimes accompanies a too-sudden change of temperature or atmosphere.
The following are all proved varieties for market work; those marked with an asterisk * are good seed-bearers. The rest give cuttings or offsets; the majority of the seed-bearers will also give offsets.