Watering and Feeding Tomato Plants

Watering and feeding during the season

Watering and Feeding Tomato Plants

The amount of water and the method of applying nutrients to the plant vary greatly according to cultural methods and the medium involved. As plants grow larger they obviously make greater demands on both water and nutrients.


Assessment of water requirement

Visual determination is perhaps the most widely practised method. Moisture meters are useful for small scale growers and can either be related to a water requirement table, or state whether the soil is wet, medium or dry. An evaporimeter is a simple piece of apparatus which, by reference to tables, enables the evaporation loss of the plants and the amount of water necessary to compensate for it to be calculated. More sophisticated equipment indicates water requirement in relation to light intensity.

The following figures apply to the quantity of water required over 24 hours by plants with a canopy of leaves and over 90 cm (3ft) tall, no allowance being made for loss by drainage or surface evaporation:

Weather Pattern

Water requirement per plant for full 24 hour day in temperate climates in


Water requirement per plant for full 24 hour day in temperate climates in


Very dull/cloudy and dull most of the day 0.14 — 0.28 1/4 — 1/2
Dull/overcast most of the day 0.28 — 0.42 1/2 — 3/4
Fairly sunny/cloudy with bright periods 0.71 — 0.85 1-1/4 — 1-1/2
Sunny/only occasional cloud 1.1 — 1.2 2 — 2-1/4
Very sunny / sky clear and sunny all day 1.5 — 1.8 2-3/4 — 3-1/4

• For practical purposes 1 pint = ½ litre, 1 gallon = 4.5 litres


Taking an average of about 9 litres (2 gallons) per week from mid spring to early autumn — about 22 weeks — this gives a total of 200 litres (44 gallons) per plant, not counting water lost in drainage and evaporation. For ring culture, polythene bags or straw bales, very considerable amounts extra to the above may be required. To calculate the amount of water delivered by a hosepipe, spray lines or other means when there is no meter, check the amount delivered per minute and then calculate how much water will be applied in a certain time. In a small greenhouse with a hose running at 9 litres (2 gallons) per minute, one merely needs to water for 20 minutes to deliver 180 litres (40 gallons) of water—common practice with about 40 border grown plants in an average greenhouse.

Mulching is a useful technique for preventing surface evaporation of moisture in border growing, using either granulated peat or short straw, taking care to add about 3.5g (4-5oz) of ground limestone per bushel/litre to offset the acidity of sphagnum peat.

Judging whether plants are over or under-supplied with water can be difficult due to nutritional complications, but over-watered plants will usually tend to go lighter in colour with a yellowing of the bottom leaves due to the exclusion of air from the growing medium and the inability of the plant to extract nutrients from it, particularly nitrogen. Apart from wilting, under-watered plants go dark green and become hard or brittle; there can also be scorching of the foliage and dry set. It is important to note also that if the growing medium becomes dry its salt content rises, making it still more difficult for the plant to obtain water and nutrients.


Feeding Tomato Plants

There is a considerable difference of opinion on whether constant or intermittent feeding is more successful, not only for tomatoes but for all crops. Ideally a plant with a constant and easily obtainable supply of nutrients and in a well prepared border soil of good physical structure containing slow-release nutrients may well enjoy excellent growth without the need for constant feeding. Conversely, soilless media have not the ability to store up nutrients in the same way as soil, and plants given only plain water will quickly become starved looking, as indicated by small pale-coloured leaves.

Much of the success of tomato growing lies in being able to balance the quantities of nitrogen and potash the plant requires. Excess of nitrogen will result in lush over-vigorous growth, while shortage will give rise to thin hard stems, with yellowing of bottom leaves in severe cases. Excess of potash will produce hard squat plants with very curly leaves, whereas shortage usually allows the nitrogen content of the soil to predominate, with symptoms of excess nitrogen developing. Constant application of liquid feeds, which can be either self-formulated or proprietary, is essential, applying the feeds in nitrogen/ potash ratio according to the needs of the plant, the same practice being followed with solid fertilizers.

It is usual to give high potash (3/1) early in the season, more balanced feeds later (2/1), finishing in many cases with high nitrogen feeds.

NOTE: This is the stock solution prepared by careful mixing in warm water. It is often diluted to 1:200, generally with a calibrated dilutor. When using a watering can the solution is 6m1 of the stock solution in 1 litre (1 fluid ounce in 14 gallons) of water.

It is impossible to predict with any degree of certainty the amount of nutrients required by plants, owing to variable drainage loss, vigour of plants, temperature levels and many other factors.

Care must always be taken not to apply either concentrated liquid or solid feeds to dry plants, as this will not only result in a rapid rise in salt concentration, but may physically damage the roots or necks of the plants due to the caustic nature of many fertilizers. When applying fertilizer in solid form, care should be taken to avoid ‘swirling’ by the use of a hosepipe, which can give rise to high concentrations in localized areas.

Foliar feeding is an extremely useful method of feeding plants, and tomatoes are no exception, but it is important to avoid the application of these feeds in hot sun, and to adhere strictly to recommended dilution rates.

Cultural systems other than border culture may require some modification to ball watering and feeding methods, especially where limited quantities of soilless media are involved. In containers constant liquid feeding can frequently result in a build-up of salt concentration and give rise to ‘black bottoms’ due to low water availability or temporary deficiency in calcium caused by high salt concentration. It is necessary to flush out with plain water on one or two occasions.

Straw bale culture may give rise to problems, a shortage of nitrogen frequently occurring early in the season due to its `locking up’ by the straw decomposition process. Later on there may be excess supply, necessitating extra potash at a time of year when the reverse is more usual.


Fruit picking

fruit picking This should be carried out with care, removing the fruit by snapping the stem, leaving the calyx on the tomato. Fruit should not be left under a hot sun, as it quickly goes soft and deteriorates. When wholesale marketing of fruit is intended, it is usually picked fairly green and must be graded according to accepted standards.

Amounts of fruit per plant vary from 3 — 8kg (6-151b) (or more). A good average is around 4.5 kg (10 lb). A material called ‘Ethrel-C’ can be used to ripen green fruit on the plant at the end of the season.

Removal of plants

At the close of the season the top of the plant is cut off 23-30 cm (9-12in) from ground-level and the rest removed with as much of the root as possible, necessitating in some cases the watering of the growing medium. Both foliage and roots should be deposited as far away from the greenhouse as possible. It is also sound practice to examine roots and estimate the degree of pest and disease attack, after which the greenhouse is then thoroughly cleaned by carefully burning sulphur at 45g /28m3 (1lb per 1,000cu ft), or by other means.


Cultural Techniques for Tomatoes

Since the early 1970s much interest has centred around hydroponic systems, in aggregate or pure nutrient solution, either in plastic mouldings or latterly in troughs, nutrient film technique (NFT), perlite and rockwool. Rock wool systems are developing very quickly in commercial spheres, as are perlite bag systems. Compressed peat, straw and wood pulp systems are also being developed.

It may take some time for these systems to be introduced into amateur growing circles, but perlite systems seem likely to be introduced before too long. Production-line methods are beginning to develop, including two or three crops per year on a concentrated basis from a succession of plants taken only to the first or second truss stages.

Single and double truss cropping

A square area of cropping in a greenhouse is able to produce a certain number of kg/lbs per year on conventional cropping. If taking the plant to ten or more trusses gives a yield of, say, 1 —3kg (3lb per sq ft), it should be possible to improve this by setting the plants closely together and obtaining 226-450g (¾-1lb) from each. Allowing a succession of crops per year there is scope for enormous yields.

Gardeners wishing to experiment with this technique in borders should set out the plants at 25-35m (10-14in) apart each way, supporting them with canes or netting and allowing two trusses to form. Under this method, however, there could be problems with soil sterilization, and poor light may limit the number of crops per year to two instead of three.

Carbon dioxide (CO2) enrichment

There has been in recent years much publicity about accelerating the growth of plants under glass by supplementing the natural complement of carbon dioxide gas in the atmosphere. In the case of tomatoes three-fold enrichment is carried out from half an hour after sunrise until one hour before sunset. Specific equipment is obtainable for the purpose, the amount of CO2 supplied for a given period being measured by weight, not volume. Burning paraffin, propane, dry ice or liquid CO2 are the various methods used, the requirement for tomatoes being 45-60kg (100-130lb) for propagation and 300-360 kg (700800lb) for the growing period per 28m3 (1,000 sq ft)


Varieties of tomatoes

Most varieties grown by amateur gardeners and commercial growers conform to a fairly standard type but there is great variation in stem colour and hairiness, leaf shape and colour, plant habit and vigour, flower and fruit, size and colour. New varieties are being constantly introduced, most of these being F1 hybrids of specific habit, some with some inbred disease resistance. The fruit colour types have a particular attraction, pale lemon, pink, yellow, tangerine, chartreuse, red with golden stripes, or brown with green stripes adding a superb rainbow effect to any salad and much appreciated by floral art enthusiasts. Most important, they are delicious to eat.

It is essential to choose a variety suited to the growing conditions, whether cold or warm, and whether a compact or a vigorous variety is required. In general practice, under amateur growing conditions, compact varieties are more useful.

27. March 2011 by Dave Pinkney
Categories: Fruit & Veg, Greenhouse Gardening, Salads | Tags: , , | Comments Off on Watering and Feeding Tomato Plants


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