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.
The young plants, being strong and sturdy, and growing steadily, will soon require more room than is available in the seed pans. Pots 3 in. across (or large 60's) may be used, and if a piece of rough fibrous loam is placed in the bottom, over a piece or two of crock, proper drainage will be secured. The soil should consist of sandy loam and leaf soil, or old soil shaken from the stools or roots of Chrysanthemums, Zonal Pelargoniums, etc, may be used if it has been exposed to the weather a few weeks or months beforehand. Early in the year it is better and safer to pot up the young Tomatoes in the house where they have been raised. A movable potting bench may be fixed up in a convenient spot, and the soil to be used should be warmed by placing a few hot bricks in it for a time if it is to be used at once. Cold or half-frozen soil from outside should never be used for potting Tomatoes or any other plants raised in warmth. The temperature of the soil, therefore, should be as near that of the greenhouse as possible, to prevent the tender young plants getting a serious check.
When potting young Tomatoes the soil should be pressed about the roots moderately firm with the fingers. Each plant should be placed in the centre of the pot (although some growers prefer placing them at one side), and the stem may be sunk down to the seed leaves, or within 1/2 in. of the first true leaf if the seed leaves have withered. After potting, the soil should be given a good watering with a fine-rosed pot. The plants should then be placed on shelves near the glass or on stages where they will receive plenty of light. For the first two or three days after potting it may be necessary to shade the freshly potted plants from strong sunlight. This may be done by spreading sheets of newspaper over them, or by letting down blinds outside, if any. Once, however, the plants have "picked up", that is, have established themselves, they need plenty of sunlight and as much air as possible on all days when the weather is genial Watering must be attended to regularly each day, care being taken to give water only to those plants that require it. When the soil is still wet from the previous day's watering it indicates bad drainage or a plant that is unhealthy in its root and leaf action. All freshly potted plants should be watered with a rosed can until the soil becomes more consolidated; afterwards water may be applied carefully from a pot with a fine spout, so as not to make holes in the surface.
Tomatoes are grown either in pots, wooden boxes, or planted out in beds or borders to develop and ripen their fruits. When the 4- or 5-in. pots into which they were moved from the seed boxes are well filled with roots, the plants will be ready for the final moving. If pots are to be used, 12-in. ones will not be too large. They should be well drained with a large "stopper" and a handful of "crocks" at the bottom. Over these a thickish layer of fibrous loam, moss, or half-decayed leaves should be placed. The compost to be used should, if possible, consist of good fibrous loam, with a good sprinkling of river sand or grit and a little leaf mould, the whole compost heap being turned over three times before using, to secure proper mixing. If a dusting of basic-slag manure is added to the soil it will be found of great use to the plants when they are setting and ripening their fruits later on. About 1 lb. of basic slag will be sufficient to mix with an ordinary barrowload of soil. When using large pots for Tomatoes, the plants should be put in deeply without disturbing the ball of soil too much. The upper third of the large pots should not be filled with soil at first, as the space thus left will be useful for adding topdressings or mulchings of fresh soil later on to maintain the requisite growth and vigour of the plants.
Instead of using pots, many growers plant their Tomatoes in what are known as "kipper" boxes. These measure about 14 in. long, 8 to 9 in. broad, and about 4 in. deep, and cost about a penny each. They are very useful, and if placed on a bed of old soil or ashes, the roots of the plants push through the slits in the bottom and secure plenty of moisture from the old compost, as well as food that will have been left behind from other plants.
When neither pots nor boxes are used, the Tomatoes are then planted out one row each along sides of a narrow span-roofed house, or several rows in larger houses.