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.
At no period in its growth does the Cucumber require a higher temperature than 90° F. to produce its maximum amount of growth and fruit; and it may be taken that a temperature from 70° to 90° is the best all-round temperature for Cucumbers. Of course, with sun heat, the temperature of a Cucumber house will often go above 90° F., but then the ventilation can be so regulated that a pure and buoyant atmosphere saturated with moisture will be maintained.
Cucumbers naturally like a good turfy loam. The top spit from a meadow or piece of pasture land, if stacked up about six months before use, and enriched with alternate layers of stable manure, or indeed any organic manure such as that obtained from the poultry run, rabbits, etc, will give excellent results. At the time of use the addition of a little lime or basic slag will also prove beneficial. The compost should be chopped down with the spade, but should not be sifted, the spade being used to reduce the turves to a sufficiently small size. When good turfy loam is not available, any ordinary good garden soil enriched with well-rotted manure and leaf mould will give satisfaction.
The first consideration is to obtain good seeds from a reliable source, as one of the first steps towards success is to have strong and sturdy plants. When two or more crops are to be grown during the year, the first sowing should be made about the first week in December. Some growers sow from twenty-four to thirty seeds in shallow boxes, using a fairly rich and gritty soil. A better practice, however, is to sow the seeds singly in 2 1/2-in. pots, making a hole with the finger or a dibbler about 1 to 1 1/2 in. deep in the centre of the compost, afterwards covering and watering in with tepid water. Place in a temperature of 70° to 85° F., the first-named being probably better for the seeds sown in December, as too high a temperature is apt to weaken the plants during the short days.
In due course the seed leaves appear through the soil, and later on are followed with the true roughish, lobed leaves, and later on still the tendrils. Once germination has taken place, plenty of light should be given, but the temperature must be maintained up to 70° or thereabouts at night. The young plants are sprinkled over or syringed with tepid water two or three times a day according to the state of the weather, and the atmosphere is kept moist and buoyant, not only to ensure rapid growth, but also to check attacks of Thrips and Red Spider - pests that soon appear if the air is allowed to become too dry.
When the seedling pots are filled with roots the plants should be shifted into 5-in. pots, or if space is available they may be planted at once in a fairly rich and gritty compost. Later crops are often transferred from 3-in. to 5-in. pots while waiting for space, and also because a good trade is done in selling the young plants to growers who have not the convenience for raising a supply of plants themselves.
Another method of raising Cucumber plants is to fill a 3-in. (60) pot about half-full of compost, insert a seed in each pot, and cover slightly with soil. When the first true leaves, after the seed leaves, appear, a little more compost is added in the way of a topdressing, almost up to the rim. At this stage the young plants, being very tender and juicy, must be handled with great care, but the topdressing will generally carry them till planting time.
When Cucumbers are grown in specially constructed houses it will pay to keep the latter in a clean condition. This may be accomplished by whitewashing the brickwork with limewash, and by burning some sulphur or brimstone with all the ventilators and doors closed as tightly as possible. This is to suffocate and kill any insect pests and fungoid diseases lurking in the crevices, etc. Two or three pounds of sulphur will be sufficient to vaporize a house 100 ft. long.
The soil to be used should be chopped down with the spade from the heap of compost, but not into too fine a condition. A little superphosphate of lime, basic slag, or dissolved bones may be sprinkled over it at the rate of a 5-in. potful to every barrowload, and thoroughly mixed by turning over.
The compost thus prepared is then placed in little heaps 2 to 2 1/2 ft. apart in the houses, about 1 bus. of soil being sufficient for three plants at first.
When the plants are large enough they should be planted in their fruiting quarters without delay. Owing to their rapid growth they soon begin to look yellowish and sickly if kept too long in the small pots. In planting, a hole should be scooped out in the centre of each mound of soil, and deep enough to allow the top of the ball of soil attached to the plant to be about 1 in. or so below the fresh soil. This should be pressed carefully but firmly round the roots and base of the stem, to encourage new roots and increasing vigour. In two or three weeks each mound of soil will be permeated with a mass of clean healthy-looking roots.