This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
These are a very useful class of plants in the autumn, and by pinching back a few of them rather late, and giving them a gentle heat, they can be had nearly all the winter. To have fine plants, a few of the best should be set aside at planting-out time, to be shifted into 6 and 8 inch pots when the pressure of that work has been got over. If good large plants are required, put them into the 8-inch pots, and one good plant will make a nice plant in the 6-inch; let them have good rich soil, with perfect drainage. If a cold frame is at liberty, they can stand in it all the growing season. If the frame is of wood, and can be raised a little from the ground, it will let the air circulate better amongst them. Here they can stand all the summer, and, with proper attention, by the end of July they should be nice plants. Up to this time all flowers should have been picked off; at this time, if any are wanted for early blooming, they can be set aside and allowed to bloom: those for later flowering may have just the very tips of the shoots picked out, which will induce them to throw out side-shoots; and by a few small stakes drawing them a little wider, to let air and light to the centre, they will make fine plants to succeed the early lot.
They will be greatly assisted if a little heat can be afforded them. After the pots are full of roots, and the flower-buds make their appearance, frequent watering with manure-water will be beneficial to them. To have a houseful of the above, in all the different shades and colours coming into bloom just as the frost is cutting them off outside, well repays all the care and attention bestowed on them throughout the summer; and then cut blooms of so many different shades of colour enliven the cut-flower basket through. November and December.
The early-flowering section of the greenhouse varieties we treat much in the same way: after the wood has been well ripened in the spring, cut them pretty closely in; when the young shoots are all fairly broken, shake them out and reduce the roots, and repot into smaller pots in a rather free compost, placing them where they can be kept close for a few days, until they take with, the pots. In a very short time the roots will have found their way to the side of the pot, when they should be repotted into their blooming-pots, using a little stronger compost this time, and making it rather firm. They can stand in cold frames, for a short time in summer, close to the glass. With proper attention, by autumn fine stiff plants will be the result. If a few of the forward-est are taken into a gentle heat, about 55° at night, they soon begin to show flowers; and if kept in this temperature, they give a fine quantity of bloom by cutting each head as they begin to open. Liquid manure should be given often, but not strong.