There are about 150 to 250 tomato seeds in a gram; usually 100 to 200 good seedlings are obtained from each gram that is sown. The weight of a seed varies considerably, according to the variety and the conditions under which it has been produced.
A high humidity at the time of their emergence helps the seedlings to shed the seed coats.
GROWING ON COMPOST
Plants that are standing `pot thick’ in beds on the floor require the least labor for watering. They can be `stood out’ in this way immediately after being pricked out. They should be spaced out as soon as the leaves of adjacent plants begin to touch; there should be 15 cm between each plant and its neighbors.
Spacing out is necessary if short, stocky plants are to be produced. Overcrowding will result in tall, spindly plants with high first trusses. If they are standing pot thick in a large single bed in one section of the glasshouse, considerable labor will be needed to space them out.
While they are standing pot thick, plants should be in relatively small beds, close to their final situation. In the type of layout shown on p. 30 no plant has to be removed more than 1 m during the spacing-out operations. Rogue plants and any that are not up to standard should be discarded then. Pegs are needed at the corners of the plots to prevent plants from being knocked over by the hoses.
Some growers prefer single rows 75 cm apart, with plants between 35 and 40 cm apart. Others prefer a double row and a wider walking path. The rows are usually about 60 cm apart and the walking path is about 90 cm wide. In some districts the glasshouse is planted lengthwise; in others crosswise planting is preferred. You would be well advised to discuss the subject with your local horticultural advisory officer.
Trickle irrigation in one form or another is becoming universal. If you lay out the harness before you begin planting the trickle nozzles will show you where to put the plants. There should be no more than 10 cm between the nozzle and the base of the plant. On soils which tend to pack it is a good idea to make a slight depression near each plant. This will check the run-off of the trickle feed. The plant should be a good deal deeper than it was in the soil in its container. This will cause a secondary root system to develop above the primary roots and give the plant greater feeding ability and greater stability. The soil in which the plants are set out should be neither cold nor unduly wet.
A sound general policy is to leave at least the top 1 m of foliage on the plant and to remove the rest. Trimming should be carried out even after the plants reach the wire. The training methods at this level vary. The inverted arch system was tried and found successful at Levin. A pamphlet describing it is available from your local MAF office. About 6 weeks before the crop is to be pulled out the plants may be stopped one leaf above the flowering truss. This encourages the upper trusses to swell, so that there is a minimum of unripe fruit at cropping time.
Too often training over the wire is done only when there is time for it. This is a pity—to neglect it is likely to significantly affect the yield.
WATERING AND FEEDING
An evaporimeter provides a more accurate estimate of the daily requirements. A simple and effective one was designed overseas. A round tray is made by slicing 10 cm off a 200-1 (44-gal) drum. A brass or copper point is welded on to the centre (or pointing inward and downward from the top edge) to act as an indicator. The tray contains about 7.5 cm of water. It is checked daily and, when necessary, replenished to exactly the same level. The tray is painted inside and out with a white, anticorrosion protective paint. A tray that is cut from a 200-1 drum is approximately 570 mm in diameter. It has a surface area of 2568 cm2, which is very close to the recommended area for a tomato plant (equivalent to one plant per 2510 cm2). Experiments have shown that there is a close correlation between the amount of water that evaporates from such an open water surface and the total water loss from a similar area of glasshouse soil plus plants. The evaporimeter is, therefore, a guide to the water loss from the whole glass-house.
It is advisable to average the loss from at least two evaporimeters in each glasshouse. They are best placed on or above the collarties, and in average conditions of temperature, sunlight, and air movement. They should be kept well away from ventilators and heating pipes, and out of any shadows.
Theoretically, the amount of water to be added to the evaporimeter each day should be equal to the amount that is needed by each of the plants to replace the water it has evaporated. In practice, there is usually a slight difference—solar radiation is not the only thing that affects the plants’ water uptake. The condition of the soil, its soluble-salts status, the type of heating system, and the health of the plants are some of the other things. The positioning of the evaporimeters, even when carefully done, may also introduce some error; however, it will be constant for the time of the year and the stage of the crop. Once determined and recorded, it can be used unaltered from season to season.
It is best expressed as a multiplication factor. Supposing that the evaporimeters need an average of 400 ml each day to keep their levels steady. Theoretically, the plants should also need 400 ml of water each through the trickle system. Reading the plants and the occasional soil check may indicate that not quite enough water is being applied after a week a double watering may be needed to restore the soil moisture level. This double watering supplies an extra 400 ml, which represents the under‑watering of a week—therefore 400/7 = 57 ml more water per day should have been applied.
Instead of the 400 ml, 457 ml or 1.1 times the evaporimeter reading was required. This 1.1 multiplication factor should be noted down and used to convert all future evaporimeter readings. (A reading of 500 ml will require a 500 x 1.1 = 550-ml watering, etc.) The actual multiplication factor can run from 0.9 to 2.0 but is usually between 1.3 and 1.4.
With a uniform cropping plan and provided there are no drastic alterations to the glasshouse or in the situation of the evaporimeters, the multiplication factors, once recorded, can be used each season, again and again. A set of notes incorporating these factors should be kept in each glasshouse, somewhere near the container that is used to check the output of the trickle harness.
Remember that it will always be necessary to keep an eye on the development of the plants. The watering rate must be cross-checked from time to time, so you will need to develop the ability to `read’ your plants.
There are several methods of watering through permeable plastics. Some commercial systems rely for their output control on small nozzles, where the water is forced through a screw thread. Lately, so-called `micro-tube’ systems have come into use. The trickle is gained by passing the water through short lengths (up to 60 cm) of very small-bore polythene tubing (0.875 mm). Microtube systems can be made quite easily at home and are cheaper than the traditional nozzle systems. They all distribute
To avoid any plant sitting continuously in a puddle, you should make sure that there is an outlet about 10 cm away from the base of each plant. It is advisable to make especially sure that the outlets of microtube harnesses are firmly in place; home-made wire staples are useful for this.
TRICKLE IRRIGATION AND FEEDING
You must therefore try to maintain the area of the moist soil and of the plant roots.
The best ways of doing so are the occasional use of the hose and the use of low-trajectory sprinklers late in the season. These treatments should begin as soon as it is obvious that the area of soil that is kept damp by the trickle outlets is contracting. You can see this from the surface, but preferably during a period of settled, bright weather. You will need to repeat this observation every 4 to 6 weeks. Any watering should be either preceded by a dry side dressing of at least 25 g/m2 of sulphate of potash or followed by at least z 1 of strong (1 in 100 or 1 in 150) high-potash trickle feed. This prevents the plants having access to water with a low salts content, which may lead to ripening disorders.
Late in the season, when all the fruit and leaves have been removed up as far as the wires, low-trajectory sprinklers can replace all the other watering methods. This mobilises the nutrients through the entire soil mass; evens out the spread of water and nutrients; and drawing the roots to the surface, allows them to ramify everywhere.
TRICKLE FEEDING SOLUTIONS
Magnesium also is supplied through the liquid feeding programmed, but the remaining major elements (calcium and phosphorus) cannot be efficiently supplied through a trickle system. They do not move freely through the soil and must therefore be applied as base dressings, dispersed through the soil by cultivation.
A simple code is used to express the potassium to nitrogen ratio of the various trickle feeds. The solutions can be bought as proprietary mixtures or made up from pure chemicals. The following table indicates the main types, with their constituents, their potassium to nitrogen ratio, and their code name.
*An average diluter bottle holds 101(about 21 gal).
Magnesium sulphate is usually added to the stock solution at the rate of 50 g/l. In many districts this has been enough to prevent any symptoms of magnesium deficiency in the crop. It is also the maximum amount the standard solutions will absorb without the salts recrystallising when the solution is kept in a cold place, such as an unheated glasshouse. If a higher magnesium content is needed the stock solution must be made weaker. Your local advisory officers will provide guidance on this point.
The chemicals that are used are crystalline (as opposed to pelleted or coated) potassium nitrate (13 percent N and 35 percent K), potassium sulphate (39 percent K), urea (46 percent N), and magnesium sulphate either as Epsom salts (10 to 12 percent MgO) or Kieserite (16 to 17 percent MgO).
Industrial-grade chemicals are preferable as they are easy to dissolve and do not leave any residue. Fertilizer-grade chemicals usually leave some impurities after dissolving. They must be removed by overnight settling or by filtering. Where necessary, a suitable dye (fluorescine, magenta, or disulphine blue) is added to keep a check on bottle contents. A stock solution is made from 6 g of the chosen dye in 1 of water, and 5 ml of this is added to each litre of the fertilizer solution.
TRICKLE FEEDING PROGRAM
The dilution rate of the stock solution and the amount of trickle irrigation that is required are to some extent related. Together they form the tomato grower’s most difficult problem.
At this stage it is important to watch the flowers. They should be well up on the head of the plant, open properly with a good yellow color, and be freely visible. Greenish flowers in tight bunches that do not open properly (`oat flowers’) or flowers hidden in a mass of lush foliage warn of later difficulties.
A glasshouse that has been flooded during crop changeover to wash out surplus fertilizers or in which a test has shown the nutrient levels to be low should be ball watered with a strong trickle solution (1 in 100 or 1 in 150, usually of a 2KN-feed).
During the rest of the season correct rates and dilutions are the key to successful tomato growing. Continue with a watering programmed based on a district schedule or on your evaporimeter readings, but corrected frequently after reading the plants and checking with a trowel the water spread in the soil. As the quantity being applied increases, the trickle solution is made weaker. A high concentration of salts in the soil water makes it more difficult for the roots to take it up. It is therefore growth limiting. A straight potassium feed at a 1 :100 dilution is the most growth-limiting feed that can safely be used; experience has shown that higher concentrations sometimes cause root damage. The weakest solution you use, late in the season, should be about 1 :350. After that, change to overall watering with hoses or sprinklers.
If the plant roots have become confined to the area under the trickle nozzles, weak solutions may quickly give rise to ripening disorders and (on lighter soils) even to nutrient deficiencies. There is little danger in prolonging the application of the stronger solutions as long as sufficient of them is being applied to allow some water to run away to drainage. A build up of soluble salts occurs from frequent applications of quantities so small that they wet the soil only to root depth and then evaporate away from the surface, leaving the salts behind. This eventually causes root damage.
Recent investigations* suggest that when it exceeds a certain concentration ammonia in solution becomes toxic to tomatoes. Urea in the soil breaks down to ammonia. High-nitrogen trickle feeds based on urea that are used at high concentrations may cause root damage. The concentrations and formulations that have been suggested in this bulletin are believed to be safe, but should not be exceeded.
There are some symptoms of water stress with which you will need to ecome familiar. They are to be found on the plant rather than on the fruit.
High salts produce slow growth, wiry stems, and short internodes. The foliage is a shiny blue-green and the leaves are hard to remove. The flowers are small and bright yellow to almost orange. The fruit is small, very dark green (especially on top), and ripens through a mahogany color to an eventual bright red.
Low salts produce a plant that grows quickly and has a thick, brittle, pale green stem. Its leaves are large and break off easily, or soon fall off. The flowers are large and pale yellow to creamy. The fruit is large and soft. It ripens through whitish green to eventual pink, and usually exhibits disorders of the blotchy ripening type. Affected plants may be found even in apparently dry soils. In wet soils they `guttate’—they produce water droplets on the leaves at night and are wet by morning.
HEATING AND VENTILATING
Temperatures that are too high or too low will adversely affect plant growth and fruit production. Hence these two factors are usually treated under the one heading.
A heating system should be designed to provide an even temperature,
Experiments indicate that from planting to picking the day temperatures in unheated houses should be between 21 ° and 24°C. After picking has begun they should be reduced to between 18° and 21 °C. This should improve the late yields and reduce any humidity problems, but it can only be managed with careful ventilation and (usually) by planting in late summer, late winter, or early spring.
A heated house provides greater temperature control. From planting to picking 18°C at night and 20°C by day are recommended, with ventilation starting at 21 °C. After picking has begun these temperatures can be lowered by about 3°C. An efficient heating system is therefore required and many growers have been dismayed by its cost. However, preliminary trial work has shown that the extra cost of the fuel is more than made up for by bigger yields at a time of higher prices.
In districts with a high relative humidity, an increase of one or two degrees in temperature will lower it and thus reduce the likelihood of disease.
Ventilation is the main temperature and humidity control. In a normal glasshouse there is ample exchange of air. Any urge to open it up early in the morning and close it at twilight should be ignored. When to open or close the ordinary shutter-type ventilators should depend on temperatures. Automatically operated ventilators are slowly growing in popularity. Which of a house’s vents are opened and how widely depend on the direction of the wind and on the inside temperatures.
Every glasshouse must have adequate provision for ventilation. The area of its ridge ventilators should equal at least one-sixth of the floor area. Side vents are desirable; they are much easier to install while the house is being constructed.
TRAINING AND PRUNING
From 3 weeks after planting remove all the laterals before they reach 10 cm in length. If they grow too big they waste plant energy and the large wounds they leave when they are removed provide an entry for diseases.
When the fruit on the second truss is of marble size, remove all the leaves below the bottom truss. Snap them cleanly off at the main stem. This helps to keep the base of the stem dry and disease free. Laterals snap off more easily when the plants are turgid.
Damp down no later than 2 p.m. in sunny weather and never in bad weather. The leaves must be dry before sunset; diseases attack leaves that are wet at night.
Overhead damping that is sufficiently forceful to shake the flowers also helps the natural setting of the fruit. If pollen drops out (`flies’) from the flower when it is shaken, the weather is warm enough for natural setting and damping down will help. If the pollen does not fly, damping down will not help.
A fungicide is added to the dilute solution to stop botrytis disease from growing on the dead petals and spreading from them to destroy the young fruit. Check on fungicide materials with your local MAF advisory officer.
A truss is sprayed when there is an open flower on it. Some growers spray weekly, others every 10 days. A very short burst into the flowers may be enough. If the plant head is in the line of fire, use your gloved hand to protect it from the spray—otherwise it may suffer hormone damage.
The classical symptoms of hormone damage (narrowness and veins that run parallel) may develop in young leaves that get a good dose of fruit-setting spray. This can be confused with hormone-weedkiller damage, but mild and scattered cases at the start of the fruit-set season are probably caused by the fruit-setting spray. They do not affect the fruit crop.
When shaking the flower causes the pollen to fly, the weather is warm enough for natural setting and hormones are not required. In marginal conditions, pollen is most likely to fly between 10 a.m. and 3 p.m., while the house is warmest. Tapping the wires and overhead damping both promote natural setting.
The sawdust mulch is pleasant to work on and by reflection increases the light in the glasshouse. It rots slowly during the season and, when the crop comes out, is worked into the ground to add to the organic-matter reserves. It does not upset the soil’s nitrogen balance when it is used in this way.
There are almost as many ways of picking and packing glasshouse tomatoes as there are growers of them. A great many ways are adaptations to suit a particular set of circumstances. There is therefore no `best’ method, but the following recommendations should ensure the highest possible quality.
Precooling is a highly effective way of overcoming this problem, of preparing the fruit for transport, and of ensuring that it arrives in good condition. Quite a small coolroom can cope with the daily output of the average property. The refrigeration plant should be rather powerful, so that it extracts the heat from the fruit quickly. Adequate air movement is also essential and a fan-assisted circulation system must be installed. Adequate air channels must be left between the stacks of fruit. Although precooling should allow you to pick the fruit at any time of day, in practice early-morning picking is still desirable because it is easier and the fruit is firm. To avoid problems with condensation, the fruit should be properly packed and the boxes closed before they are put into the coolroom and stored until they are to be sold.
WHEN TO PICK
HOW TO PICK
Tomatoes with the calices on. Special emphasis is placed on large, starry, bright green calices. In volume-fill packs this practice often leads to damage from stem punctures that occur both in transit and in the shop. It is arguable whether a grower who produces out-of-season tomatoes in the high-quality grades should not go the whole way and use a tray pack to take maximum advantage of the attractive calices that many of the newer varieties have.
Clean—free from dirt, dust, insect stains, or other foreign substances and materials.
3. Sizes—there shall be four sizes only:
(a)large—exceeding 65 mm in diameter,
5. Unclassified—tomatoes which have not been classified: The term `unclassified’ is not a grade, but is a designation to show that no grade has been applied to the lot.
6. Labelling—cases containing tomatoes should be labelled and all labels should provide windows to allow for separate recording of grade, size, colour, and market line number.
The following program has been adopted by the Horticultural Research Centre:
This program was designed to reduce the risk of pests and diseases being carried over from one crop to the next. By the end of a season tomato mosaic virus is usually infecting all the tomatoes in glass-houses. It is not controlled by chemical soil-sterilisation–the smaller the quantity of infected residue there is lying around after a crop, the less risk there is of a disease carryover to the next crop. Sweeping up leaf debris and forking out the roots are particularly important steps. Separating the two jobs reduces the risk of infected debris being buried in the soil.
Pests and the spores of such diseases as botrytis and leaf mould on a glasshouse structure and on the surface of its soil are killed by the formalin wash down which precedes the forking out of the roots. These pests or diseases might otherwise be buried in the soil during the removal of the
Sterilising glasshouse soils to kill or inhibit pathogenic organisms is an essential step in successful tomato growing. For the first one or two seasons you may achieve success without sterilisation, but inevitably fungous diseases and probably such pests as eelworm will establish them-selves. Unless they are checked they will continue to develop until crop yields are reduced. Some will cause the death of plants at any stage of their growth.
Heat is undoubtedly the most efficient means of sterilising soil. In tomato glasshouses it is usually applied as steam. Unfortunately this requires a special steam generator which, with its ancillary equipment, is expensive. The usefulness of steam lies in the fact that it will control all the pests and diseases and most of the weed seeds in an area that is efficiently treated.
There are various means of getting the steam into the soil—grids, steam ploughs, and the `Hoddeson pipe system’ are the main ones. Whatever the system, it should destroy any pathogenic organisms while damaging as little as possible those that are beneficial. At 82°C most pathogens are destroyed but some (notably tobacco mosaic virus) are resistant. Where this is a problem the soil temperature should be raised to as near 100°C as possible. The chart below shows the thermal death point of various organisms.
Several chemicals can be used to sterilise soil. Formalin is an excellent fungicide but does not control eelworm, viruses, or weed seeds. Also it is messy to apply and requires a considerable volume of water if it is to penetrate the soil.
Chloropicrin is the most commonly used material. It gives good control of most pathogens, but does not readily penetrate undecomposed plant material. For this reason, it is not satisfactory on its own where eelworm has been a problem. Also, it has no effect on virus diseases.
DD gives adequate control of eelworm and is frequently used with chloropicrin to control most soil-borne pathogens. Methyl bromide gives excellent control of weed seeds and of eelworm but indifferent control of fungous diseases. Granular chemicals are available and have proved effective, provided they are used strictly according to the directions.
Dosage rates and methods of application vary with the chemical. Your nearest horticultural advisory officer will advise you as to the most suitable material and how to apply it. There are however a few basic points to observe for any treatment to be effective :