Expert Tips for Growing Vegetables in the Greenhouse

How to Grow Vegetables Under Glass

Growing Vegetables In the Greenhouse

Not everyone uses their greenhouse for growing vegetables.  The majority of glasshouses are used for ornamental plants, but it is possible without inconvenience, to grow quite a nice selection of vegetables and to have them available when outside crops are scarce. It has long been known that the intensity and duration of daylight have a marked effect on the time taken by vegetable crops to reach maturity. This has to be taken into account when planning the sowing and planting times of suitable vegetables.

growing vegetables in the green house

Lettuces are among the easiest to manage and may be sown from early autumn onwards, the earliest sowings being ready for cutting within ten to twelve weeks. Later sowings can be made to provide crops over a long period, in fact it is possible with the aid of a greenhouse or frame to have lettuce available throughout the year.

For heated houses suitable varieties are: Amplus, Greenheart, Cheshunt Early Giant, Kloek and Grand Rapid., The simplest way is to sow the seeds in boxes, and later prick off the seedlings into other boxes.  Even with the greatest care, the seedlings are bound to receive a slight check at the time of pricking of and a further one at the time the plants are moved to their final positions, when they are about 8cm tall. Some check can be avoided by sowing the seed very thinly in beds in the greenhouse and then making the one move when the plants are big enough to handle.

A suitable sowing temperature is 12 to l5°C. although after germination has occurred heat can be decreased to 10°C. Plenty of ventilation will induce sturdy growth.

Whether lettuces are being grown on the greenhouse floor or on the bench, the aim should be to space them at least 18cm apart each way.

When growing vegetables in the green house such as carrots, they can be grown with success in the warm greenhouse, the sowing period for the early varieties extending from autumn to spring. First sowings will be ready for pulling in the New Year. They grow best on light loamy, sandy soils having a good humus content. Fresh organic manures are best avoided unless incorporated into the soil some months beforehand.

Some gardeners ‘chit’ the seed. To do this, soak it in water for about twenty four hours before sowing, spread it on a sheet of glass and cover with a moist cloth. As soon as the seeds sprout, mix them with an equal quantity of fine sand which makes sowing easier.

Choice of varieties is important the best forcing varieties having sufficient, but not too many leaves. Among these are Early Nantes and Amsterdam Forcing. Turnip Early Snowball can be treated in the same way as carrots although the chitting is not needed. Use the roots while they are small.

Chicory is also worth growing in the cool greenhouse. Roots can be lifted from the open ground in autumn. Prepare them by cutting of the leaves 25mm above the crowns, as they are lifted. Shorten them to a uniform length of about 20cm Then cover with a mixture of clean, sandy loamy soil, free from stones. Some growers force chicory successfully under the benches of a greenhouse.

A reasonable degree of moisture should be present to give the chicory its bright appearance. After heeling in the roots, leave them for two weeks keeping them in darkness. Increase heat to 20°C. but after three days reduce it to l5°C and later to 12°C. After four or five weeks the heads or chicons, should be ready for cutting. Washing the heads prior to use, adversely affects their keeping qualities.

Radishes can be grown successfully under glass so long as there are adequate supplies of organic matter in the soil. A close, hot atmosphere promotes leaf growth at the expense of the root. Sow seed in deep boxes, glasshouse bench, or in the greenhouse ‘floor’ soil.

Moderate heat is necessary, and if the light is reasonably good, a temperature of 8 to 10°C will be suitable. Any attempt to force growth during dull weather will result in plenty of foliage but little ‘bulb’. Watering the growing crop is normally unnecessary and undesirable, although it is advisable to apply sufficient moisture to the soil before sowing, so there is enough to carry the crop to maturity. Short-topped varieties are best, including the forcing strain of French Breakfast, Sparkler and other turnip-shaped varieties.

A few roots of mint can also be brought into the greenhouse for winter production. Grow these in boxes or large pots, or on the greenhouse floor. Lay the roots flat in little trenches about 8cm deep and start them under cool conditions. Once growth is seen breaking through the surface a temperature of 10 to 13°C. is suitable. A few fine mist sprays of water will provide the required atmosphere making it possible to cut shoots over a long period.

Rhubarb can be forced under the staging, darkness being necessary if this crop is to be a success. Lift the roots from outdoor beds in early winter. Many gardeners leave them exposed to a few frosts before housing. Pack them closely together, filling the spaces with loose soil as work proceeds. Then give a light watering to settle the soil around the roots. If a temperature around SOC. is provided for a week or so, growth will soon commence.

Later, heat can be increased to 10°C. and subsequently to l5°C. Good varieties for forcing under the staging or in a darkened corner of the greenhouse, are Prince Albert, Victoria and Timperley Early. It takes five or  six weeks from planting time until they are ready for pulling.

Seakale can be grown in the same way, although since the roots are much smaller, they can be forced in large pots or boxes. Darkness is essential, otherwise the blanched roots will be unpalatable.

Dwarf French beans can be grown in pots or boxes in the cool greenhouse. For this purpose it is best to use 23 to 25cm pots well crocked containing fairly rich compost. Fill the pots to three parts of their depth and space seven or eight beans around the edge of the pot covering them with 3cm of soil. Subsequently, the number of plants can be reduced to four or five.

Lightly syringe the plants at frequent intervals. This ensures the flowers set well and keeps down red spider. Once the pods have set it is a good plan to apply liquid manure at ten day intervals. To keep the plants upright, place twiggy sticks in the pots. The aim should be to maintain a temperature of 12°C or so, although no harm is done if it rises a little during the daytime. The plants appreciate fresh air but not draughts. Good varieties are Masterpiece and The Prince, both having long fleshy pods with a good taste.

Mustard and Cress can be sown in pots, boxes or on the greenhouse staging soil according to the quantity required. Sow little and often using a good compost made fairly firm and watered well. Do not cover with soil but apply brown paper to provide darkness, or stand the boxes in a dark position for a few days.

So that they mature together, sow cress four days before mustard. The latter will germinate within three or four days and both should be ready for cutting within seven or eight days.

Peas can be cultivated in pots or the greenhouse border. For pots, rely on dwarf varieties such as Kelvedon Wonder and Little Marvel which can be sown in winter for an early crop. The 25cm size pots will take six seeds. Sow them 40mm deep around the inside edge of clean, well crocked pots, filled to rather more than two-thirds of their depth, with a mixture of three parts good fibrous loam and one part each of leaf mould or peat and silver sand.

After sowing, water the pots and stand them on a shelf near the glass. As growth proceeds gradually till the pots with more compost.  Avoid high temperatures keeping heat to 18°C during the day with 5°C lower at night.

For border culture, provided the soil is good, fork over the ground, working in a dressing of bone meal at the rate of 3 or 4 oz to the square metre. Sow in winter in drills about 4cm deep either in single rows or staggered. Provide twiggy sticks at an early stage and as growth develops suitable supports should be used.

Occasional overhead sprayings are beneficial. If the soil is moist before sowing it should not need watering very frequently. Keep the temperature from rising above 18°C.

Heated frames equipped with both soil warming and space heating, ought not to be left idle during the winter for they can be used to produce forced vegetables at little cost.

Make up the bed in the frame with care. If the intention is to force vegetables in pots or boxes, soil warming cables should be placed so that they are covered with 5cm of sand and the boxes placed on top. Where it is intended to grow plants in the soil bed in the frame, the cable must be covered with soil which is fine and good. The depth of the bed should ensure that the plants are near the glass without touching it. The roots must not come into contact with the electrical hot bed layer.

Once the bed is ready, the glazed lid should be placed on the frame for ten days or so. This will give weed seeds time to germinate. Leave the bed exposed to the weather for a week in order to get the soil thoroughly moistened. A few days after the lids have been replaced, switch on the current.

The following are among the crops which will succeed in a heated frame. Carrot, Amsterdam Forcing, of which seed should be sown in shallow drills 15cm apart and where the bed is 15 to 18cm deep. Thin the seedlings so they stand 5 to 8cm apart. Plenty of moisture and ventilation are needed. A day temperature of up to 15°C is desirable. The crop should be ready from ten to twelve weeks after planting.

28. August 2010 by Dave Pinkney
Categories: Fruit & Veg, Greenhouse Gardening | Tags: , | Comments Off on Expert Tips for Growing Vegetables in the Greenhouse


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