THE CULTIVATION OF MELONS UNDER GLASS

These are traditionally grown in low, rather narrow houses where it is possible to maintain a temperature of about 27°C.

Note for horticultural students

Historically melons have not cropped up in the examinations questions over many years. The subject is included in this text partly because countless students have had to study it before; and because there is quite a bit of teaching value in perceiving the difference that the melon crop has compared with most other such crops. It is a fertilised fruit and so in sharp contrast with the traditional glasshouse cucumber, which is not. Some of the modern small melon types may carry many more fruits than the 2 per plant of Blenheim Orange and are much easier to grow. Melons were one of the first achievements a Victorian gardener could grow for the household. Now that imported outdoor-grown melons are so cheap to buy, few gardeners will ever enjoy the anticipation or face the fun and challenge involved in melon growing.

Seed sowing – the traditional system

Seeds are raised by sowing singly in pots of turfy loam and sand, or the John Innes Seed Compost, keeping them in a brisk temperature of at least 27°C and covered until they germinate. On germination, the plants are kept growing on steadily, eventually being transferred to 125mm.

Planting

When the roots are running well in the pots, they should be planted out on previously prepared ridges of soil. These ridges, which should be about 300mm wide and 225mm high, are made up of good turfy loam of a rather greasy nature, to which has been added a little rotted stable manure and a sprinkling of bonemeal and sulphate of potash. This ridge of compost should be well firmed before planting and warmed through. When planting at about 450 to 600mm apart, the ball of soil should not be entirely covered, but about 25mm of it should be left projecting. This will ensure that no moisture lies about the base of the stem.

Training

Take the growing points of the plants up to the roof, tying in the laterals as they appear. The lower laterals should be stopped to allow the upper ones to develop.

Pollination

Wait until about four female flowers are open on each plant, and then hand fertilise. Allow two or three fruits per plant, and as they grow, support them by nets.

Aftercare

Keep the ridges well supplied with moisture, and feed two or three times with dried blood. As the fruits ripen, lower the temperature a little, reduce the humidity, and give less water to the plants. Cracks will develop round the base of each stalk and there will be a sweet melon smell present.

Prevention of fertilisation

Insects, mainly bees, must be excluded, and this is done by tacking nylon net 6mm size over the ventilation seating or a coarse type canvas is used for the same purpose. This can be tacked on to the edge of the ventilators when open and also to the seating, so that ventilation can be given when necessary. If fruits are fertilised, the ends swell, and have a bitter taste, making them unsaleable. Male flowers are taken off in the early stages from the base of the main stems.

Feeding

Feeding should begin about a month after planting. Liquid feeds with a potash-nitrogen ratio of 1 : 214 are suitable and one example is 0.67kg urea and 0.34kg potassium nitrate to 4.5 Its water used at a dilution of 1:400 for all waterings. Dry feeding with fertilisers with a similar potash-nitrogen ratio can be used at about 60g per metre run of the bed. Later feeding consists of nitrogen only. If plants are being grown on straw bales, feeding should commence 2-3 weeks after planting. Traditional beds can be mulched with stable manure, well shaken out to avoid damage from fumes during the growing period. Avoid manure coming in contact with the base of the stem by using a small mound of sterilised soil.

Straw bales must be free of pesticide contaminants.

Old cucumber bed material (re-steamed) is often used. Very good results may be achieved by growing on treated straw bales but the majority of the growers now use NFT or a Rockwool derived system which keeps a nutrient-rich water film available to the roots.

Training

Several methods are at present adopted, one being to stop the lower laterals at one leaf joint, and the higher ones at the second or third leaf joint. Sub-laterals on the lower part of the plant may be stopped at one leaf, and the ones higher up at the second or third leaf joint. Too hard a system of stopping is thought to reduce yield. The overall crop is often similar to that from ordinary training methods, but a higher earlier crop could be expected from the cordon system, due to a higher planting density. It is usual nowadays to grow cordon-trained crops.

In essence this is a system of training up a single stem to wires stretched horizontally 150mm apart. The plant is stopped at about 900mm to encourage the lower fruit to swell more rapidly and then a side shoot is carried on upwards as the leader. No cucumbers are allowed to grow off the main stem. The first laterals are stopped at the second leaf joint and the sub laterals after the first leaf: overall to retain two fruit-bearing joints on each lateral. All the growths are tied in, all the male flowers removed and all the fruit encouraged to hang down properly. Some alternative commercial systems tend to twine the stem of the plant around an inclined string. This involves less tying and trimming which reduces the cost of the labour. The all female cucumbers tend to reduce the chance of male flowers and hence the pollination risk.

Temperatures and ventilation

A moist atmosphere is essential and a night temperature of 17°C is needed. Day temperatures can run up to 24°C and ventilation is given above this level.

Watering

Irrigation systems are normal in commercial practice. In general, the aim is to keep the borders moist, but to avoid waterlogging, which will quickly damage the roots, and can lead to loss of the fruits in the early stages. The amount of water will vary with the compost, but usually, two waterings a week will be needed, plus daily damping overhead, once or twice a day depending on weather. (Most commercial growers use either NFT [Nutrient Film Technique] or Rockwool. Both of these techniques involve much more frequent watering, including liquid feed and may be as much as ten waterings a day for Rockwool).

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