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.
A salad of some description is at all times essential in most establishments, and if not forthcoming when required, it may prove vexatious to all concerned. Although good salads can be made without Lettuces, much better can be made with them; a well-grown Cos Lettuce, in my opinion, forming the very best of salads, and one which few would decline. Cabbage Lettuces are very good, but not to be compared with the Cos, especially if they have to be sent a distance, and, in addition, are supposed to keep good at least for three days. Cabbage Lettuces should be used quickly; even then they are invariably much too flabby in salads, and are only grown by me on account of their earliness, and their adaptability for late sowing also. The little Commodore Nutt is a very hardy, though not very early, variety; and a number of autumn-raised plants planted on a south border prove very serviceable should the Cos varieties be lost. If by any chance the stock of autumn-sown plants of either kind be small, seed should at once be sown of the Early Paris Market Cabbage Lettuce, and with this a good variety of the Paris White Cos. The seed may be sown thinly in pans or boxes, using fine light soil, and placing on a gentle hotbed till germinated, when they should at once be transferred to a shelf near the glass, but still in a growing temperature.
When in rough leaf the seedlings may be pricked out in shallow boxes, placing these in a frame on a gentle hotbed; or if many plants are required, a layer of about 4 inches of fine soil may be spread in a frame over a slight hotbed, pricking the seedlings into this about 3 inches apart each way. Use tepid water for watering; and keep the frame rather close till the plants are established, when air should be given freely, hardening them off so as to be ready for their final quarters from the middle to the end of April, according to the locality. The Cabbage variety will be first fit for use, and by growing a good quantity the Cos variety need not be cut till it is near perfection. In mild localities, if a good breadth of spring-sown Cos Lettuces are planted, the seed of those to succeed may be sown on a south or south-west border, either where they are to mature, or for transplanting. In cold districts it is advisable to sow more seed early in March on a gentle hotbed, with or without glass covering, pricking the seedlings either into boxes or a sheltered spot, and finally transplanting to a warm border.
Lettuces delight in a deeply dug, heavily manured soil, which should be made rather firm. The small varieties may be put in rows 9 inches apart and 6 inches asunder in the rows, and the rows of the Cos varieties 1 foot apart and 9 or 10 inches asunder in the rows. Tying up hastens blanching, and is usually resorted to with the Hick's Hardy White Cos and the Black-seeded Brown Cos, but is quite unnecessary in the case of the Paris White Cos varieties. The Black-seeded Brown Cos is not so liable to run to seed as the latter. For this reason, a few plants of it may with advantage be grown with every batch of White Cos, and at times may prove invaluable for the prevention of a break in the supply.