GROWING GREAT GLASSHOUSE TOMATOES

Varieties

F1 Varieties for quality and yield include:

Adonia Estrella Eurocross A

These are all disease-resistant.

PREPARATION FOR PLANTING

Planting and routine work

Tomatoes are grown commercially in many types of house. Generally speaking however, large, airy, span-roofed houses, running north and south are most usual. There are two chief types:

i) the vinery which is usually 8 – 9m wide, 1.35m to the eaves, and 3.83m to the ridge,

ii) the 4.5m wide Venlo type which is now popular.

Tomatoes are also grown successfully in Dutch light structures. Heat is not essential, and late crops can be grown in cold houses. For early crops heat is, of course, necessary: desirable temperatures for seed raising are about 20°C, and precise recommendations exist for growers sowing in the depths of winter. Growing on temperatures are best in the region of 15 – 18°C and ventilation at 23°C. If tomatoes are heated much over this the yields are reduced. Commercial growers introduce additional C02 (carbon dioxide) to 0.01% in the hours of daylight in the early part of the season (when the vents are mostly shut) as this increases yield.

Picking the fruit before it is ripe increases the plant’s total fruitfulness (but many amateurs may appreciate the extra sweetness of a fruit ripened on the plant).

At the end of the crop, the plants are best removed carefully and the roots burned. (Composting them would not destroy with certainty the eelworm cysts or such noxious diseases as the stem rot Didymella – a problem in the Channel Islands.) Wash the house down with a detergent and remove all debris. This thorough hygiene treatment reduces pests and diseases like red spider mite, white fly and tomato virus disease problems from overwatering.

Varieties Superlative Blenheim Orange Hero of Lockinge King George Best of All

Scarlet flesh

Scarlet flesh

White flesh

Scarlet flesh

Green flesh

Medium size

Popular variety

Suitable for cool conditions

Can be grown under cooler conditions

Good flavour

PESTS

Red spider mite

Can be troublesome on established plants from early May onwards. Some smoke fumigants can be used. There is a useful red spider mite predator (Phytoseiulus persimilis) – a predaceous mite which can be introduced into the glasshouse to achieve some control.

White fly

Can be controlled by pyrethrum-based sprays. The white fly predator (Encarsia formosa) can be introduced.

Derris is safe, also the white petroleum oil emulsions.

The tomatoes may be stopped at 4, 6 or 8 trusses for convenience: commercial growers need all the trusses they can get and frequently they layer the plants, lowering the ‘vine’ on to a simple support and maintaining the growing point at a convenient height for working – about 1200 – 1500mm. In this way the actual vine of the tomato plant – its stem length, can grow to 10 metres. The side shoots are removed – pinched out small and with little problem. The old leaves are broken off carefully. Both of these techniques aid air circulation.

DISEASES AND PESTS

In very humid conditions several diseases may occur:

Botrvtis – the grey mould – this grows commonly on dead material but it may take a hold on a wound perhaps left by a broken off leaf. Such infections on the stem are very serious; the ‘canker’ can be cut out if small enough and the wound only painted with creosote.

Leaf mould is a fungus with many strains. Fortunately the breeders of tomato varieties have bred resistance into the types available but occasionally a problem occurs. Control is not easy once the disease is well established but prior to that point, good ventilation and the chance of the leaves to be dry is enough to keep the risk of infection low.

Potato blight which also attacks tomatoes can be devastating. Outdoors it is bad enough causing discoloured and ruined fruit, but under glass all the foliage may be killed in a couple of days with no second chances. (So be very careful to keep potato crops away from tomato crops and also to spray to control potato blight or cut off the potato foliage if there is a problem starting.) Good ventilation and ample air circulation dramatically reduce the risk of these problems.

The fruit may also suffer from buck eve rot – a fungal infection common for amateurs because they tend not to use sterilized soil. Water splashed about may lead to the infections carried from the soil. It also seems to be worse for crops which occasionally dry out.

Diseases affecting the roots include phytophthora and foot rot, brown and corky root rot, fusarium wilt, verticillium wilt and yet more.

Virus diseases reduce yields. These include tomato mosaic virus (TMV) which also reduces fruit quality by causing bronzing. (Some cultivars of tomato are resistant to some TMV strains, TM-1, TM-2, TM-3, are three such factors for resistance.)

Soils

Most soils will grow tomatoes, but reasonable depth is essential and the drainage must be good. The soil has a considerable effect upon varieties. Few commercial growers use soil because of the sterilisation costs and the much higher yields available from culture in Rockwool and/or by the Nutrient Film Technique. Many amateurs find ring culture easy and productive.

Winter flooding

This is necessary to replenish the soil moisture reserve, and to wash out salts left from previous manuring. The amount to give is sufficient to bring the soil to field capacity, which means to wet the soil fully, but without water running away in drainage. This may vary according to the amount of water given to the previous crop. About 33,000 Its per ha could be needed, 33 litres per metre or if the soil is dry, up to double that amount. Water should be applied over three applications. Spray lines with nozzles are often used. If soil has been steamed apply water prior to the application of base fertilisers.

Base dressings for traditional crop systems

A tomato crop of 120- 192 tonnes per ha. 0.4 ha uses:

360 – 585kg K20,

180 – 270kg nitrogen,

31.5 – 67.5kg phosphorus,

49.5 – 76.5kg magnesium, and 225 – 360kg calcium.

In watering about 20% of the nitrogen and up to 15% of the potash applied may be lost in drainage.

Ring culture

This system works with well filled large pots of J.I.P.3, open at the bottom and standing on polythene lined troughs filled with aggregate (gravel). The plants are supplied with nutrients from the pot and water from their roots in the gravel. The aggregate should be watered daily and the pots only when they dry out. Frequent feeding with liquid feeds is a great help – twice a week at least when they are growing well, with a dilute high potash feed as may be prescribed by Bio, Phostrogen, Solufeed or other proprietary source.

Traditionally the tomatoes are planted into warm soil and into the hole the supporting string may be placed. This avoids having to tie a string to the bottom of the plant. As the plant

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