Planting Tomato Plants General Guidelines

As the main source of light in the northern hemisphere is southerly (conversely in the southern hemisphere), it is advisable to plant in rows running north-south to avoid restriction of light, or alternatively to plant on the square system. Commercial planting distances allow between 25,000 and 30,000 plants (or more) per hectare (10,000 and 12,000 per acre), but for all practical purposes in smaller greenhouses it is usual to allow about 0.372m2 (4 sq ft) of border area or trough per plant for the total area of the greenhouse which means about 45 x 45cm (18 x 18in) or 65 x 35cm (26 x 14in) or thereabouts. Spacing is not a vital matter, but close planting is not generally advised, as while it may seem at first sight to guarantee a larger crop, the reverse is often the case, as it restricts air movement and encourages disease.

Whatever system of culture is involved, the planting of tomatoes must not take place until a temperature of 14°C (56-57°F) can be achieved in the growing medium at a 13-15cm (5-6in) depth, as checked by a soil thermometer. With this must go the proviso that light levels must be suitably high, a matter for adjustment in relation to the selected cultural programme. Heating systems must obviously be operating sufficiently in advance of planting time for the necessary temperature level to be achieved. This of course shows the benefit of well-designed’ systems capable of imparting radiation warmth to the soil in addition to raising the air temperature to the level stated.

Where very early crops are involved, special care must be exercised; it is folly to plant automatically on a certain date every year, when the soil may still be cold. Early crops are planted in good light areas with efficient heating systems from mid winter to late winter onwards, although for the majority of amateur gardeners with a fair level of heat, early spring to mid spring is the most usual time, waiting until mid spring or late spring for crops grown without heat.

Plants should ideally be 30-35cm (12-14in) high at planting, with the first truss of flowers fully developed and showing colour on one or two blooms for the early plantings, so that the developing fruit will act as a brake on rank vegetative development, especially in rich media. For planting in borders generous holes are taken out at the appropriate distance apart with a trowel or planting tool a few days before actually planting, to allow the soil at the sides and base of the hole to be warmed by solar radiation and air currents. Plants are then set out with reasonable firmness, the seed leaves an inch or so above soil-level. Previously watered plants in clay or plastic pots should be carefully removed by tapping them out on a hard surface; paper or peat pots and blocks can be planted intact and can be left on the surface to root gradually but not allow to dry out. Should plants be unduly leggy, perhaps because planting is delayed by another crop such as lettuce, they can be layered by setting the plants on their sides.

With other systems of culture the same general procedure should be followed, but in all cases take care to check planting distances.

Successful establishment

The first task of the young tomato plant is to establish itself successfully, and to achieve this the roots must develop out from the root ball into the growing medium. Where the growing medium is too wet and cold, air will be excluded and the production of new roots inhibited to the extent that they may die back and become infected with weak pathogens. The young plant will often put out new surface adventitious roots in an effort to survive, but a checked plant will inevitably collapse in the end. A dry growing medium will also hinder root development, as will a heavy concentration of soluble salts.

Ideally, therefore, the growing medium should be rendered compatible with the production of new roots in respect of temperature, moisture and soluble salt content. Soil temperature and moisture content are issues which can readily be checked whereas soluble salt concentration cannot (without a salt meter), although troubles in this direction should not arise if preliminary soil analysis is followed by careful base fertilizer application. With formulated growing media it is essential that these be obtained from a reliable source or correctly mixed. If, on the other hand, a plant is able to develop new roots with great rapidity, especially in a heat sterilized soil rich in nitrogen and ammonia, it can rush into non-productive vegetative growth.

Air temperature should also be at the desirable level, it being especially important that night temperatures do not drop excessively in relation to day temperatures. High humidity encouraged by frequent damping down and avoidance of too early ventilation will also assist with the establishment of plants. In completely cold greenhouses (with no heating), establishment of plants can be very difficult, particularly during periods when cold nights are followed by hot days. But when environmental control equipment is available to regulate temperature and humidity within fine limits, successful establishment is relatively easy.

Support, training and pruning

There are several ways of supporting tomato plants — tying to tall canes, or better still by the use of 3-5 ply fillis, Italian hemp or polypropylene twine (the last mentioned in many ways being preferable to string), tied in a loose knot above the cotyledons but under the lower leaves, and secured to a sufficiently strong horizontal wire 1.8 — 2.4m above ground-level, and firmly secured to the structure (fully laden tomato plants are extremely heavy). The plants are carefully twisted clockwise round the twine as they grow. Netting and plant wires are often used for oblique and layering systems of training. Training methods are extremely varied, and may be summarized as follows:

Vertical training (A) Plants are stopped on reaching horizontal wires on short-term cultural systems. On long-term crops plants are arched over wires (A2).

V-training (B) Plants are trained out obliquely and alternately in different directions. Useful with straw bales where plants are set closely together.

S-hook system (C) This involves the use of 16 gauge S-hooks set 35cm (14in) apart, plants being supported so many hooks along and dropped a hook as the season progresses, thus being progressively layered obliquely at an angle of 30-35°. Wires or hooks should be used to prevent bottom truss trailing on growing medium. At ends of row plants are turned on to next row (C2).

Layering (D) Initially trained vertically, plants on their strings are detached before reaching the horizontal wire, and dropped to an angle of 30°, usually when lower trusses are picked. Layering in all its forms allows greater stem lengths at a convenient height.

Lateral training (E) The plants are trained obliquely at a 35-40° angle, wide mesh or polypropylene netting being a useful supporting medium. Tie plants on to netting with loops of string or wire/paper clips. Lower plants as season progresses. Interlocking hooks or similar devices can also be used.

The above image shows the use of a simple frame fitted over a growbag. Choice of any particular training system will depend on length of growing season, type and height of greenhouse, consistent with access to plants and whether there is adequate ventilation to avoid the problem of disease which frequently occurs in systems other than vertical, due to restriction of air movement.

Training systems for tomatoes depend greatly on the space available and length of growing season.

Pruning

Side shoots are removed when small and the lower leaves when they start to yellow, indicating that they have served their purpose. Opinions differ on the severity of de-leafing, but generally speaking defoliation up to the ripening truss is sufficient to allow free circulation of air. Leaves are best removed when the plant is turgid, with a quick up-and-down movement, although a knife can be used, making sure that no snags are left. Plants are generally stopped at a certain height, both to facilitate their handling and to restrict unproductive development of foliage at a time when flowers are unlikely to set and form fruit.