This section is from the book "The Gardener V3", 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.
Too much cannot be said in praise of this most useful section of the Stock family. Grown ever so carelessly, they yield a good supply of flowers; but when grown in pots and carefully tended, they produce in the spring and early summer masses of blossoms, almost unequalled by any other plant at the same time. No gardener who has a house to be kept gay should be without them, nor should the amateur cultivator who has a frame and a spot of ground at command.
Seed should be sown in June, using boxes filled with a light rich soil, distributing the seeds equally but thinly over the surface, and covering to the depth of eighth of an inch, and watered through a fine rose. The boxes should be placed on a somewhat shady border, and be covered with a hand-glass or some such protecting agent; or they can be placed in a pit or frame, admitting air, and keeping the surface of the soil nicely moist. This will secure a perfect germination of the seeds, and robust growth. Shading must be employed should the sun shine directly on the hand-glasses or pit in which the boxes are placed; but the less shading the better, if it can be dispensed with, as one result sometimes is, to cause the plants to grow weakly, and render them liable to damp off.
When the first leaves are fully developed, the plants may be pricked off into boxes, in rows 3 inches apart each way, retaining as much soil as possible about the young roots when transplanting them. A rich light compost should be used; and when the process of planting is done, and a gentle watering has been given, the boxes can be placed in the frame, and some shading applied for a few days till the roots lay hold on the soil. When growth sets in the lights can be removed, and the plants wholly exposed to the action of the elements.
All that is now required will be frequent waterings of the plants as necessary, and keeping them free from weeds, until the flowers begin to form in the leading shoots sufficiently to distinguish the double-flowering from the single-flowering plants. Then comes the process of potting the double-flowering plants; and here a little care will be requisite. By this time the roots of the plants will have so penetrated the soil as to make it possible for the soil and plants to be lifted from the box bodily and placed on the ground; then carefully divide it so that each plant shall have a good portion of soil adhering to the roots. Meanwhile a compost for potting should have been prepared - say, of old turfy loam, chopped fine, one half; of leaf-mould, river-sand, and well-decomposed cow-dung, equal parts, mixed well together, using pots large enough to take the ball, and employing good drainage. A good watering should be given, and the plants placed in a cold frame, shading from the sun till they are thoroughly established.
To secure a good growth, keep the soil moist, and shift into a larger-sized pot if, and when, necessary. Keep the plants symmetrical by pinching out irregular growths, and apply moderately-strong liquid manure as soon as the plants are well established in their blooming pots. An airy cool position near the glass should be given them during the winter, and frost should not be allowed to reach them. A liberal feeding will develop fine flowers, and they will be found of great service in the decoration of the conservatory when fully in bloom. A. K.