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.
In small houses the main stems are trained up beneath the glass until they reach the ridge board; the top is then pinched out. All side shoots - "laterals" as they are called - are suppressed as they spring from the axils of the leaves. The sap is thus kept moving up the main stem from the roots into the leaves, where it is converted into flowering and fruiting material under the influence of sunlight. The more light the better; consequently it is a mistake to plant too closely, and about 18 in. should be left between the plants when trained up beneath the glass.
If several wires, about 1 ft. apart, have been tightly strained from end to end of the house, about 6 or 8 in. from the glass, it will be found a great convenience. As the main stem reaches wire after wire, it should be tied with raffia, keeping the stem on the under side of the wire. There is always a natural inclination for the shoots to push against the glass. If allowed to do so, they often get scorched and deformed by the heat, what many gardeners call "basilheaded", whatever that means. In any case, the tops should be kept away from actual contact with the glass, and the layer of air between the leaves and the glass will temper the scorching rays of the sun in summer, and enable the leaves to carry on the work of assimilating food under more comfortable conditions. Many growers place a bamboo cane to each plant, and where this can be afforded it helps to keep the main stem in place when tied.
When in full growth, Tomato plants require plenty of water at the root; the stems and leaves require none. The temperature of the water should never be lower than that of the house in which the plants are growing, and if a degree or two higher so much the better. The tanks should always be kept full, so that the chill may be taken off. In very large Tomato houses, where no tanks are used, but water is applied direct from the main by hose pipes, there is a certain amount of irregularity in watering that is difficult to avoid. Some plants get too much, others too little, and although the work is done more quickly, and more cheaply, the crops are by no means so large as when water is given properly to each individual plant. In giving water the main point to remember is to give sufficient each day, and neither too much nor too little. If the soil is soddened with water the roots become chilled, the leaves begin to curl, and the flower buds begin to drop, because the food they require from the roots is not forthcoming in sufficient quantity. On the other hand, unless a sufficient amount of water is given, the plants are unable to obtain their nourishment from the soil, and again the flowers and even the young fruits fall off.
It is a common practice with market growers in all parts of the kingdom to mutilate the leaves of their Tomato plants, especially when the fruit begins to colour. There are very few indeed who allow the healthy leaves to carry on their natural work, but these few invariably get heavy crops of fruit. It is a popular fallacy that light is absolutely essential to develop the colour in the Tomato fruit. And yet every grower probably knows from experience that the brightest-coloured and most luscious fruits are often to be found beneath the leaves, completely hidden from the sun. They also know that the imported fruits are picked almost green, and that they colour in complete darkness in the hold of the ship during transit. Crocuses colour underground, and Grapes are shaded from strong sunshine by the vine foliage, and yet colour. And yet, notwithstanding these well-known facts, the great majority waste time and money in having work done that is more of a hindrance than a help to their plants. A reference to the work carried on by the leaves of plants (see Vol. I, p. 44) will convince anyone that so long as the leaves of a Tomato plant are clean, green, and healthy they are performing the important work of feeding and ripening the fruits. When leaves, therefore, are cut away, or only partially cut away, as shown in the annexed drawings, the wounds caused have first of all to be healed up before the mutilated remains can proceed with their work of absorbing the carbon (which, apart from water, forms the great bulk of the plants and fruits) from the atmosphere.
The only leaves that should be removed are those that are turning yellow at the base, and those showing the slightest traces of fungoid disease, and these should be burned immediately instead of being thrown on the rubbish heap.
Fig. 495. - Common Example of Reckless and Injurious Defoliation.
Fig. 496. - Tomato Plant, partially defoliated and injured.