Tomatoes growing techniques explained

In late summer or early autumn enjoy tomatoes grown outdoors, or extend the season by growing them in a greenhouse.

The tomato plant is vulnerable to frost and wind, and the earliest and best crops are produced in greenhouses. You can also grow selected varieties outdoors. Tomatoes can be grown in greenhouse borders, outdoor beds, growing bags or large pots -outdoors or in a greenhouse.

Container growing is sensible in greenhouses as it prevents a buildup of pests and diseases in the border; it is also ideal on a patio or restricted area outdoors.

There are three basic types of tomato:

Tall-growing or indeterminate types have a main stem that can grow many metres long if not stopped. They need training up canes or strings, side-shooting and stopping. Most are greenhouse varieties, though some shorter, jointed types thrive outdoors. The training system is referred to as cordon growing.

Bush or determinate types have a compact, bushy habit. They don’t normally need staking or stopping, but shoots are sometimes thinned. This type grows outdoors – fruit quality can be improved by using glass cloches standing on end. Dwarf types reach a maximum height of 25cm (10in), perfect for patios or hanging baskets.

Fruit sizes range from large, fleshy beefsteak types to tiny cherry tomatoes. Fruits may be round or plum-shaped, regular or ribbed. Red, yellow, orange and striped fruits are available.

Soil and site preparation

Tomatoes like rich, moisture-retentive soil. They grow best in a sunny, sheltered spot – against a south-facing wall is ideal.

Check for germination after four days. As soon as the seedlings appear, transfer them to the light. When two true leaves form, prick the seedlings out into 7.5cm (3in) pots of potting compost. If you have sown seeds in pots, thin out to one strong seedling per pot.

The seedlings are ready for planting out or potting on when they are 15-20cm (6-8in) tall and flowers are visible on the first truss.

To make life easier, you can bypass the sowing stage and buy ready-grown plants from nurseries and garden centres, although the choice of varieties is limited. Choose sturdy, dark green plants about 20cm (Sin) high.

Growing tomatoes outdoors

Move tomatoes outdoors when the risk of frost is over, at the end of late spring or the beginning of early summer. Water the pot, then knock each plant out gently. In open ground Set plants 45cm loam-based or soilless compost.

Plants growing in the open soil benefit from a black polythene sheeting mulch. This keeps weeds down, retains soil moisture and reduces soil splashes. Spread the sheet, fix firmly along the planting rows and set out the young plants through slits in the plastic.

Water plants frequently in dry weather and, once small tomatoes form on the first truss of flowers, feed weekly with a liquid tomato fertilizer, following the manufacturer’s instructions.

Pinch out the top of tall varieties when small tomatoes form on the fourth fruit truss. This prevents further flowering and encourages the tomatoes to swell.

Crops can be advanced by two weeks by setting out the plants under cloches in the middle of late spring. Place cloches over the prepared bed a fortnight before planting out to warm up the soil.

Tomatoes in a greenhouse

In a cold greenhouse set out young plants as soon as the risk of frost is passed. Water the pots well be-forehand. In a heated greenhouse set out young plants as soon as the first flower truss is visible. Keep the temperature at night to a min-imum of 10°C (50°F).

In a border set the plants 38-46cm (15-1 Sin) apart. Lay growing bags or pots out on the floor or staging. Set out two or three plants in each bag, or one in each 23cm (9in) pot.

Support each plant with a tall stake and tie. Or tie a slack string under a leaf joint near the base of the plant, attach it to the greenhouse roof and twist the plant stem around the string.

Remove side shoots regularly and pinch out the top of the stem when plants reach the greenhouse roof or when small tomatoes have formed on the sixth truss. Water regularly, especially if plants are container grown.

When tomatoes form on the lowest truss, start feeding with a liquid tomato fertilizer. Keep the greenhouse well ventilated and shaded. Damping down aids fruit setting.

Harvesting

Crops should ripen outdoors from late summer to early autumn, depending on the weather. In an unhealed greenhouse, pick fruit from mid summer until mid autumn. In a heated greenhouse pick from early summer until mid autumn.

Hold the tomato in your hand; press the stalk with your thumb to break it neatly just above the fruit. Before the first frost cut all green trusses and move them to a warm greenhouse or windowsill indoors to ripen. Or loosely wrap individual fruits in paper and place in a drawer. To speed up ripening, put a ripe tomato in with them. Check for and remove any rotting ones.

What can go wrong

Watch out for glasshouse whitefly, aphids, eel worms and wireworms. Root diseases, especially in greenhouse borders reused for tomato growing, can also be a problem. Grey mould often develops in damp, poorly ventilated conditions; and tomato leaf mould and virus diseases can be troublesome. Greenback and blotchy ripening are fruit disorders largely caused by unbalanced feeding. Blossom end rot arises when watering is inadequate. Magnesium deficiency causes yellow foliage; foliar sprays with Epsom salts correct this in all but the most severe cases.

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