This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Among the best varieties are Dwarf Frame (Plate a cloches), Paris White (Blonde maraichere), Paris Market (Grise maraichere), and Paris Green (Verte maraichere) - the two last-named being useful for open-air crops during the summer and autumn, the others for cloche work in winter and spring.
Seeds of both Cos and Cabbage varieties are sown at the end of August or early in September under cloches, the quantity sown depending of course upon the object in view. This first sowing may be made on nicely prepared soil, or on old hotbeds having plenty of humus and a spongy texture. To define the area for seed-sowing the imprint of a cloche is made as many times on the surface as there are patches to be sown within the circumference. Soon after the seed leaves are well developed the seedlings are carefully transplanted under other cloches on soil already nicely prepared for their reception. Either 2 or 2 1/2 dozen seedlings are thus pricked out under each cloche, as shown in the diagrams.
Two-and-a-half Dozen Seedlings under a Cloche.
Two Dozen Seedlings under a Cloche.
Fig. 529. - Showing how Seedling Lettuces are Pricked out under Cloches.
Here, again, French and English methods are quite dissimilar. The English grower waits until his seedlings have made a few large leaves and have become somewhat drawn by overcrowding. Indeed, he dare not prick out earlier unless he has some close frames and nice soil at hand, as the tender seedlings would never stand the removal to the open ground. The French grower, however, having cloches and frames always at his disposal, as well as a nice soft spongy soil, can transplant the baby plants with impunity, because he can protect them with glass, can keep the air around them sufficiently humid, and can protect them from strong sunshine or frost if need be.
As about 1000 seeds of Lettuce can be sown under each cloche, it is easy to estimate how many little seed beds are to be prepared at any given time.
Another point to be noted is that the French maraicher nearly always uses his index finger instead of a dibber for pricking out seedlings, and in this way can dispose of some thousands of plants in one day.
It has already been pointed out that when the frames for Carrots and Radishes have been sown the beds are cropped on the surface with Cabbage Lettuces, these being dwarfer growing than the Cos varieties, and quite near to the glass without actually touching it. About forty-nine plants (7 by 7) go to each light, and so far as the first early crops, or primeurs, are concerned, the main point is to watch the ventilation. The Crepe, or Petite noire, Lettuces require but very little air, and this is a great advantage before Christmas, when severe frosts often prevail, and it would be a risky proceeding to open the lights too much. The first crops are mature by the end of November and during December, and they may be seen neatly packed in shallow crates in the London markets before Christmas - not always the finest examples, it is true, because those usually go to Paris, Berlin, Amsterdam, and other big Continental cities, where salads are more highly appreciated than they are in England during the cold weather.
The Cos (or Romaine) Lettuces are raised in the same way as the Cabbage ones, but are matured under cloches instead of in frames, owing to their height. Under each cloche, however, a sowing of Radishes and Carrots has already been made, as in the frames; then the Cos Lettuce is placed in the centre, and three or four Cabbage Lettuces are placed around it, making four or five Lettuces (as shown in the diagram, fig. 530) and several Radishes and Carrots altogether under one miniature greenhouse having a surface area of 1 1/2 sq. ft. Each cloche will therefore yield, three or four Cabbage Lettuces, one Cos Lettuce, about five bunches of early Radishes, and three or four bunches of early Carrots, altogether worth from 2s. to 2s. 6d. And this system of cropping is repeated about three times between October and the end of April and May. If prices are good one can realize that the business is a lucrative one, notwithstanding the expense of manure.
Fig 530. - Diagram illustrating Hotbed and Cloches with Nine Rows of Lettuces.
(2) The thin circles show second position of cloches, the arrows indicating how they are moved.
(3) The dotted circles show third position of cloches moved as indicated by arrows.
About February, when the weather is getting warmer, the spaces between the cloches are utilized for other Cos Lettuces. As shown in the diagram, six rows are planted, each row of cloches being flanked with two rows of Cos Lettuce, making (with the three rows under the cloches) nine rows altogether on one bed 4 1/2 ft. wide. It is obvious that the Cos Lettuces under the cloches, being warmer and more comfortable, are growing at a more rapid rate than the others, and will therefore come to maturity sooner. This is what actually happens, and in March the Cos Lettuces under the cloches are cleared for sale. Two things immediately follow this operation. First, the cloches thus freed are placed over three other rows of Cos Lettuces, and the spaces left vacant by the departure of the first crop are once again filled with young plants, thus still keeping up the nine rows to the bed.
Moving the cloches from Crop No. 1 to Crop No. 2, although a simple matter to the maraicher, is a somewhat puzzling proceeding to the novice. The arrows indicate the way in which the cloches should be moved - in a north-westerly direction, it will be observed. In the first place, however, the cloche at the extreme north-west corner must be taken away altogether, and placed at the extreme south-east end of the bed. With one cloche missing it is thus a simple matter to move the others one after another over the second crop of Lettuces in the way shown in the diagram, the cloche taken away at first being, of course, available for the last plant in the bed.
About a fortnight after this movement of cloches the Cos Lettuces beneath them will naturally have grown more quickly than those exposed. They will then be fit to pull, and another movement of cloches and another replanting will take place. This time, however, the cloches will be moved due south, over Crop No. 3, as shown by the arrows in the diagram. This ingenious system of protecting one crop of Lettuces after another with the same bell glasses goes on until the end of April or May, when there is no longer any necessity for protection.
From this period and throughout the summer months the Lettuces are grown in precisely the same way, cropping and intercropping proceeding with regularity. But the plants are not left to the tender mercies of the weather as in British market gardens. They are watered every day (except when a heavy rain falls), and during the summer months, when the -thermometer registers 80° and more in the shade, perhaps the plants will be watered in the afternoons as well as in the mornings. The beautiful dark spongy mould drinks the water up readily, and notwithstanding the great evaporation of moisture from the plants themselves, and from the surface of the soil, there is an abundance of humidity, which with the heat causes the crops to grow with extraordinary rapidity. Thus the gardener is kept constantly at work marketing one crop, and immediately filling its place with another as fast as he can go. Why cannot this open-air system of cultivation be practised on an acre or two in British market gardens during the summertime at least? It would pay much better than having 5, 10, or 15 ac. under Lettuce, and losing half the plants by lack of culti-tivation. In the course of twelve months a French maraicher must clear something like a quarter of a million Lettuces off 1 ac. of ground, to say nothing of the Radishes, Carrots, Spinach, Corn Salad, etc, he obtains between whiles.
There is only one trouble in Lettuce growing in frames and under cloches, and that is mildew. During the winter season this is sometimes troublesome, and is caused by a fungus called Peronospora gangliformis. Should the white frosty-looking mildew appear, any plants badly affected are carefully taken up and burned; slight attacks are kept under by dusting flowers of sulphur over the plants and soil, or by watering with a solution of sulphate of copper - 1 oz. to 100 pt. of water. Slugs are kept down by dressing with powdered lime or soot. Cockchafer grubs, when troublesome at the roots, cause the leaves to wilt; they are then searched out with the finger and destroyed. Wireworm grubs are trapped with pieces of potato or carrot. As a rule, however, owing to the constant turning over of the soil, these insect pests are not allowed to become too troublesome.