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.
To be able to supply well-blanched and crisp sweet Lettuce nearly every week in the year, requires a considerable amount of forethought and attention, and is a result very much valued and relished by those who are lovers of salads. To have them in good condition early in May in the open air, make a sowing of the Hardy Brown or Brown Bath Cos on a bed of light rich soil from the 8th to the 20th of August, according to soil and locality. On light early soil the latter date is sufficiently early. It is of importance to get fine Lettuce, the least likely to run to seed, at any season, that good cultivation should be adopted at the beginning, and attended to throughout their whole growth. The seedling-bed should therefore be well manured with rotten dung, deeply dug, and well pulverised, and have an open sunny exposure, so that the plants may be stocky and strong. The seed should not be sown thick, as it is of importance that a crop which has to stand outdoors unprotected should not be drawn and blanched from being thick in the seed-bed. To get the sowing fit for use as early as possible in the open air, the bottom of a south wall is the best place to plant them.
A border from 2 to 2 1/2 feet wide, measuring from the wall, well manured and worked, is the position generally chosen for this crop. When the plants are about 2 inches high, which is generally the first week of December, they are ready for transplanting from the seed-bed into the wall-border. Put two rows in the width named, and the plants 6 inches apart in the row; and in performing this operation avoid the too common mode of drawing the plants from the bed with the hand, instead of using a fork to raise them, in order to preserve the tap and other roots as entire as possible. Planting should not be performed when the soil is wet; indeed, the best time to plant is immediately the border is dug. The surface should be first raked rather finely, because the great enemy of Lettuce in autumn and winter is the slug, and a rough lumpy surface affords them the best hiding-place, and renders measures for their destruction - such as dusting with hot lime and soot - less efficacious. As soon as planted they are watered, and kept regularly moist, should the weather be dry, till they take hold of the ground and begin to grow.
Beyond keeping them free from falling leaves, and occasionally stirring the surface of the soil, they require no further attention till March. In case of very severe frosts, a few Evergreen boughs, or some straw strewn amongst and over them, prevents them being severely crippled, and so kept later in being fit for use.
In March, a rich piece of ground on an east or west border, well enriched and deeply dug, is prepared whereon to plant every other plant from the wall-border. Those transplanted plants are lifted with a small ball of earth and planted a foot apart each way, so leaving those from which they are thinned at the same distance. The moved plants form a succession to those allowed to remain on the earliest aspect. When the thinning-out is completed, fork up the surface with a steel fork, and give copious supplies of water in warm weather. On light dry soil a mulching of manure is of great service. A Lettuce that is allowed to become leathery and bitter is amongst the most distasteful things a garden can supply, while a highly-cultivated crisp one is among the most acceptable. Those who can afford to cover part of those by the wall-side with hand-glasses, as the French do with cloches, will of course be favoured with much earlier Lettuces. When the genuine variety of the Hardy Brown Cos is procured, they rarely ever require being tied up to blanch them properly, unless it be a few at first for the purpose of getting these blanched as early as possible.
This variety of Lettuce, when well blanched outdoors in May, we have always regarded as amongst the most crisp and pleasant-flavoured grown.
To keep up an unbroken succession, it is necessary to sow more seed in heat, to be forwarded, so as to come in before those transplanted from the bottoms of walls are over. About the middle or end of February sow either in boxes or in a bed of soil where a temperature of 60° can be had. When large enough to handle, and before they become in any way drawn, prick up into frames about 2 inches apart each way. About a couple of feet of tree-leaves trodden into the frame and 4 inches of light rich soil answer this purpose well. As soon as they begin to grow freely more and more air should be given, until the lights are taken off entirely for a while before being planted out. When planted out, a portion of them is put on an early south aspect, and a portion on a later exposure, so as to form a succession. Rich soil, and in all respects liberal culture, are necessary for them. At the time the early sowing is put in in heat, a sowing is put in on an early border under hand-glasses, or in a cold frame, to form a succession to those sown in warmer quarters.
For these two sowings I prefer the Paris White Cos, which is in all respects a superb Lettuce.
To keep up an incessant supply of Lettuce all summer and autumn it is necessary to sow at intervals of ten or fourteen days. And in England more particularly, where the summers are hotter and Lettuce more apt to run to seed, it is a good plan to plant from the middle of June till the middle of July on north borders, and to manure, water, and mulch liberally. Another excellent practice is to sow in drills a foot apart, and as soon as they are in rough leaf thin out to 6 inches between the plants; and finally thin out every other plant, transplanting those last removed to make a succession. Making three or four sowings in this manner during the heat of summer is one of the surest ways of keeping up a supply, as they are not so apt to run to seed as transplanted plants. In the heat of summer, on light soils in hot parts, it requires liberal doses of manure and deep trenching to produce fine Lettuce; while in Scotland, in ordinary seasons, I have seen the very finest Lettuce produced on Celery-ridges planted in June. The great depth of soil afforded by the ridge to some extent accounts for this result.
After the middle of July the sowing of the more tender summer varieties should be discontinued, for they are apt to suffer from damp when the colder and damp nights of autumn set in; and the finer and more blanched, the more susceptible they are of being injured. Two sowings of the Hardy Brown Cos made about the 12th and 24th of July keep up a supply till December. The earlier of these two sowings will give the last supply from the open ground, and later sowings can be lifted and put into frames as soon as there is danger of frost severe enough to injure them. Where there is accommodation, another sowing of the same sort should be put in the first week in August, to be planted in open cold pits or frames, where they can be protected with glass to bring them safely through the winter for early spring supply, for if above a certain size they do not stand without protection. Thus there are a lot of plants fit for use in the early part of November, either to be protected where they are grown, or to be carefully lifted with balls and put under the protection of glass if possible; and a later set to put under glass, to be fit for use from Christmas onwards through the winter. They are as much likely to be injured from a damp stagnant air in frames or pits as from frost.
The situation should therefore be open and well exposed, and well aired on every favourable occasion.
The varieties of Lettuce that are found most acceptable are the Cos varieties. The Cabbage varieties are more apt to be termed frothy by butlers, and I have known them objected to entirely by some salad epicures. The Neapolitan and All-the-Year-Round are, however, excellent Lettuce; and the Hardy Hammersmith is useful from its hardiness, for if sown in August it stands the winter well and comes in early. The little-known Gothee variety, which makes a compact hard head close to the ground, is fine-flavoured, and stands longer than any other before running to seed. The Paris White Cos, London Market Cos, Moore Park, Alma, and Holme Park, are all excellent Lettuce, and form sufficient variety, with the hardy sorts previously referred to, for almost any establishment.