Growing Fruit and vegetables in a greenhouse

What vegetables can be grown in the greenhouse?

Edible crops usually called ‘vegetables’, although some are botanically fruits, include the following: tomato, cucumber, sweet pepper (capsicum or pimiento), courgette, aubergine, French bean, climbing French bean, new (early) potato, lettuce, radish, beetroot, carrot, and mushroom. Various herbs can be grown for winter use, and a number of crops such as asparagus, rhubarb, chicory and seakale, can be blanched or forced . Mustard, cress, and more recently a wide range of sprouting vegetables, are also popular if there is enough warmth. Many of the basic vegetables of the outdoor plot can be harvested earlier if they are started under glass before planting out.

What fruits are suitable for growing in the greenhouse?

The melon is easy for most home greenhouses, and the cape gooseberry (Physalis edulis) has also recently become a popular crop. Strawberries are often grown, although frames are also suitable. Suitable varieties of a number of stone fruits, such as peach, apricot, and nectarine, are ideal for training on the rear wall of a bright lean-to. Figs can be treated similarly, but they also make a good tub plant. Oranges and other citrus fruits need only frost-free conditions and are often grown for their sweet smelling blossom as much as for the fruit. Most big houses of the past had an ‘orangery’, although the plant tubs were usually stood outdoors for the summer.

I have heard that tomatoes and cucumbers cannot be grown together. Is that true?

Not any more. Modern varieties of cucumber—especially the F1 hybrids—are extremely vigorous and very easy to grow. They are not nearly so exacting as to temperature and environmental conditions as the old varieties, and usually do well if grown in the same greenhouse as tomatoes and under similar conditions. Another factor that makes this practical is the introduction of pesticides that can be used on both crops. At one time the cucumber family was prone to damage by many of the chemicals used to control tomato pests.

I cannot spend as much time in my greenhouse as I would like. It seems that ring culture might be just what I need for my plants. Can you explain how it works?

It is used mostly for tomato-growing, but it can be adapted for other crops, particularly cucumber and any especially vigorous grower. It is especially useful for gardeners who have to leave the greenhouse unattended for long periods since, when properly set up, it can maintain even root moisture. The plants are grown in bottomless flowerpots or cylinders—usually made from fibre and about 225 m (9 in) in diameter—filled with a suitable potting compost (John Innes No 3 is ideal, but any equivalent proprietary compost will do if recommended by the maker of the equipment). The cylinders are placed on a bed of aggregate consisting of clean shingle or peat kept nicely moist. The water can be applied from a can or hose or, preferably, by one of the automatic watering systems. Diluted liquid fertilisers are applied to the compost within the cylinders where the fine nutrient-absorbing roots will form. The water-absorbing roots form low down and will take up moisture from the aggregate.

What are the basic environmental conditions needed for quality greenhouse tomatoes?

Firstly, select a good variety from the seed catalogues of the leading firms. Do not, if possible, grow in the ground soil ; or, if you have to, graft the seedlings on to what the seedsman calls KNVF rootstock, also grown from seed. (The letters ‘KNVF’ refer to various root pests or disease organisms against which this type of rootstock has good resistance).

Try to maintain even environmental conditions: wide fluctuations are the cause of many troubles, such as poor pollination, flower and fruit drop, under-sized fruit, and cracking skins, as well as fungus troubles such as blossom-end rot. Attend to de-sideshooting promptly, removing any shoots growing between the leaf stalks and stem. While the fruit is developing, the greenhouse temperature must not exceed 28°C (80°F); otherwise the red pigment of the fruit fails to form and your tomatoes will suffer from blotchy ripening, greenback, and other ripening problems. Shade your glass with white electrostatic shading if necessary, but avoid heavy shade.

Can you recommend some different types of tomato varieties? ‘Moneymaker’ has had such powerful and persistent publicity that it is sometimes difficult to get people to try the many newer and superior introductions. There are improved forms of ‘Moneymaker’, and it remains an outstanding cropper; but there are also many varieties with a much greater resistance to the many diseases that attack the tomato. The F2 hybrid varieties are all worth considering first; the following are fine examples of the many different types. ‘Alicante’ has become a favourite for general culinary use in recent years. ‘Big Boy’ is a very large-fruited variety with firm flesh but excellent flavour. ‘Sweet’ is an excellent small-fruited variety, producing masses of cherry-sized tomatoes. ‘Golden Sunrise’, with its excellent flavour and general quality is overcoming the British prejudice against yellow varieties. Finally ‘Ida’, a very new variety, is especially recommended for growing in unheated greenhouses.

Do I need to feed my tomatoes?

Yes. Special proprietary tomato feeds are available; these are usually formulated to give the high concentration of potassium which the crop particularly needs. It is more useful in the early stages of the plant’s development, and towards the end of the season it is best to replace the high-potash feed with an ordinary balanced pot-plant feed. Tomatoes often show a deficiency in magnesium by the foliage yellowing from the edge inwards with perhaps only the veins remaining green. This can be corrected by watering or spraying with Epsom salts (magnesium sulphate) at the rate of 6-12 g/1 (1-2 oz/gal) of water.

I have heard that cucumbers are a difficult crop. Is that true?

To grow this crop out of season needs warmth and care, but it is easy to produce excellent greenhouse cucumbers for picking from about late May to autumn. The modern varieties are excellent; look especially for the all-female varieties you will find in the seed catalogues of leading firms. These can often be left to grow as they will, with the minimum of interference. Even if left untrained they are very productive as young plants, but proper training will ensure continuity of cropping.

Can you explain the basic technique for growing cucumbers?

The seed usually germinates quickly if sown on edge at a temperature of about 15-18°C (60-65°F) in a propagator during March or April. Transfer to 88 mm (3 ¼ in) pots, and later plant in 225 mm (9 in) pots or grow bags when well rooted. Place these containers on the greenhouse staging and train the plant as a single stem up the greenhouse side to the eaves by removing any side shoots that may form. When this stage is reached, run strings or wires along the roof from end to end or from the glazing bars to cover the area above where the plants are sited and a few feet beyond either way. Space the strings 150-200 mm (6 to 8 in) apart and train the stems under them. Sideshoots (laterals) can then be allowed to grow and should be led along and tied to the strings. When a fruit forms, stop the lateral about two leaves further on. Secondary laterals will form and should be treated similarly. For varieties that are not all female, the male flowers without a tiny cucumber attached must be promptly removed as a routine before they open—otherwise the fruit will become club-shaped, seedy, and possibly bitter.

I am fond of sweet peppers and would welcome advice on how to grow them.

These have become very popular in recent years (they are widely but incorrectly known also as capsicums, the correct name, of Spanish origin, being pimiento). They are easy to grow, especially the newer hybrids. Culture in the early stages is similar to that for tomato, but they can be grown in 175-200 mm (7-8 in) pots quite well. They usually need no support or special treatment, but the number of fruits that form sometimes need restricting, by picking some off at an early stage, so as to give the rest enough space to swell and develop properly. The fruits can usually be gathered green or through any stage of ripening to a full gold or red colour from summer to autumn; they are eaten raw or cooked.

Are melons really a suitable proposition for the greenhouse?

A number of good greenhouse varieties will be found in the seed catalogues. They should be sown and trained exactly as described for cucumber except that the supporting strings should be spaced about 250-300 mm (10-12 in) apart. A vital difference in growing is that the melon flowers must be pollinated. Pick off a male flower and transfer the pollen to the female flowers, which have a tiny fruit attached. When pollination is successful the little fruits will soon begin to swell. Do not permit more than about three or four fruits to grow on for each plant. Any others should be picked off. The large fruits may need support with nets which can be improvised from net curtain or string shopping bags. Do not harvest them until the fruit is properly ripe: the end should be springy to the touch and emit a fruity fragrance.

Is it possible to grow lettuce all the year round in my greenhouse?

Yes—but it is more sensible to regard lettuce as a greenhouse or frame crop for the colder months of the year, since in the heat of summer greenhouse-grown lettuces tend to ‘bolt’ (run to seed) and fail to form nice crisp hearts. It is very important to sow varieties specially developed for the purpose—not all lettuce will grow well under glass. Examples of good varieties include ‘Kwiek’, ‘Kloek’, ‘Sea Queen’, ‘Emerald’, and ‘May

Queen’. Sowings can usually be made from August to March for cropping from about November to late spring.

I want to improve the output of vegetables in my greenhouse. Can you tell me something about catch-crops and how and when to grow them?

These are crops that take up very little space and can be grown in between main crops, such as tomatoes or lettuce. They are usually salad crops, such as early carrots, pulled in the very young state, and radish, which can be sown almost the whole year round.

I would like to grow grapes, but I have heard that growing and maintaining a grape vine is difficult. What do you suggest?

The vine is certainly one of the less easy crops, and ideally it should be given a house of its own. In old-fashioned greenhouses, with brick sides to waist-level, the vines are planted immediately outside and led in through a specially made hole. In a modern glass-to-ground structure you can plant a vine in the greenhouse border; but take care that the roots do not dry out—as tends to happen in a small greenhouse. A vinery offers conditions that are not liked by most other plants—notably shade from the vine itself and lack of heat in winter—but I have successfully grown camellias in pots in a vinery. If you wish to grow a vine and have only little space, it is possible to get good results by using pots or small tubs. However, this does mean that the useful life of the vine is limited and a fresh start has to be made from time to time.

Sorry, comments are closed for this post.