Indeterminate Tomatoes

The object of the following description is to supply basic information about growing tomatoes in soil and on rockwool. We did not have the intention to be complete but want to supply some guidance that may serve as a supplement to the practical knowledge of the grower.

The information provided is based upon Dutch experiences with growing tomatoes. Although this leaflet is written according to the most recent information available, we do not accept any responsibility if the expected results are not achieved. Furthermore we do not guarantee the same results in all environmental conditions. Growing anywhere else in the world may well necessitate a different interpretation. Nevertheless, we hope that it may serve your needs and that you will be successful in growing tomatoes.

When using plug trays, use trays with drain holes in the plug bottom. Several sowing substrates can be used. Peat-sand compost is mostly used. Do not sow directly on the soil but on benches. Provide enough drainage to avoid water from staying in the seedbed risking Pythium infection.

When sowing directly without the use of plug trays, do not sow too dense, this will result in thin and weak seedlings. Sowing in rows is preferred to make optimal use of the available light.

Moisten the substrate well before sowing. After sowing, cover the seeds with 0.5 cm of vermiculite, sand or peat dust. A layer of plastic will be placed directly on top to maintain humidity in the seedbed. Instead of plastic, a layer of paper or jute can also be used, but the use of plastic is preferred.

Use white styropor plates on top of the seedbeds to reflect the sunlight and keep the temperature down.

Place the sowing boxes or trays on open benches above the heating pipes. The distance between the benches and the pipes should be large enough (min. 50 cm) to avoid excessive temperatures. The use of benches will result in a more homogenous temperature. Germinate at an optimal temperature of 23°C, day and night. After 5-6 days the seedlings will come up. As soon as several seedlings appear, the plastic has to be removed from the sowing bed. This should be done either early in the morning or later in the afternoon to avoid excessive evaporation around midday.

Maintain a moist soil by watering the seedbeds when necessary. The best method is lifting the plugs or soil and check by hand. When water is needed, use a very fine water spray and avoid large droplets from hitting the seedlings. When the seedlings are kept too dry, the seed husks will remain on the seedlings.

When the plants are large enough to be handled without causing damage, usually 11-12 days after sowing, the seedlings or plugs can be transplanted into soil blocks or plastic pots. In this stage the two seed leaves are fully erect and the first real leave is approx. 5 mm in length.

A good size soil block is approx. 10 x 10 x 10 cm. Avoid planting of seedlings early in the morning, because at this time the seedlings will be crisp and fragile resulting in damage. When planting in the morning is necessary, do not water the seedlings the night before to avoid fragile plants.

When having sown in a soil bed, transplant by lifting the soil by hand from underneath, loosening the soil and carefully placing the seedling in the soil block. Avoid pulling the seedling from the soil. When placing in the block, press the soil towards the seedling, making sure the roots are in good contact with the soil. When sowing took place in plug trays, a "spike bed" can be used to lift up the plugs from the tray.

A common technique is to plant the seedlings upside down in the block. This way the plant will be shorter and more erect in development. The stem of the seedling will also be into contact with the soil over a longer length, resulting in more root development.

When placing the young plants into the propagation greenhouse, leaves should never overlap those of neighbouring plants to make optimal use of the light.

It is very important to prevent the plants from rooting into the soil underneath the blocks. The best method is to use "plastic saucers". When placed upside down underneath the block, the soil block will not be into contact with the soil and the water will be drained properly.

Another method to prevent the roots from entering the soil is the use of white plastic strips on top of the soil. This white plastic will stimulate light reflection as well.

In general a small stick will be placed into the block after 25 days, preventing the plant from falling down. Do not push the stick through the block into the soil and use a rubber band to prevent the plants from falling. Have the soil on the propagation room properly leveled to avoid the plants from falling. Depending on the light conditions and the growth of the plant, the blocks should be re-spaced several times. Re-space to a final density of 16 plants/m² (depending on the plant weight the grower wants to achieve and the season).

It is preferred to water the blocks from underneath by using a hose or drip irrigation. Use water with a minimum temperature of 16-17°C. The soil should be slightly convex to stimulate good drainage. Good drainage is needed to avoid soaking of the plant blocks, encouraging Pythium infection. Saturate the plants completely after placement in the propagation greenhouse.

Depending on the soil conditions, fertilizer is added to the water. Watering must be done according to the demand and growth of the plants. The E.C. (salinity) has to be lower than 2 mS/cm when touching the leaves to prevent leaf damage.

Optimal temperature for Plant raising is 23-24°C, day and night. When the light conditions are good enough, day temperature can be raised to 25°C. Having the night- and day temperature close together will result in having short internodes and a good initial development of the first three trusses.

When both the night- and day temperature are too low, the plant development will be too slow, the plant will be too short and the 1st cluster will be too low in the plant.

The glasshouse should be equipped with several sensors for recording air temperature, heating and ventilation. These sensors should be fitted in central positions at the height of the crop. Prevent direct heat radiation onto the plants from heating pipes placed near the plants. If possible hang the pipes at a height of 2 m above the plants. Keep the heating pipe temperature on a minimum of 45°C when using 4 pipes per 3.20 m department. Start heating a day or two before transplanting to heat up the soil properly.

The temperatures recommended for growing young plants are related to defined stages of plant development. A general guideline is as follows:

r	Day	Night
Germination (day 1- 5):	23°C	23°C
Day 6-11:	23°C	23°C
Day 12-24:	23°C	23°C
From day 25:	22°C	22°C
	21°C	20°C
t	20°C	19°C
t up to day 40:	19°C	17°C

The soil temperature should be in the same range as the night- and day temperature.

The temperature mentioned are indications. Temperature may fluctuate slightly, according to the growth of the plants. Decrease the temperature one or two weeks before planting out to produce strong plants. A temperature of 23°C during 9 days is resulting in 9 leaves under the first truss. When there are less than 9 leaves under the first truss, the plant will be too generative to start with, resulting in a smaller yield.

When the plant is developing too thick stems it is recommended to slightly lower the night temperature. A larger difference between night- and day temperature will stimulate a larger distance between the internodes and cause the plants to stretch. A high 24 hrs temperature (average calculated temperature) will also stretch the plants.

Larger difference Day- and Night temp.	Plant will be stretched. Internodes are larger.
Smaller difference Day- and Night temp.	Plant will be compact. Internodes are shorter.
High 24 hrs temperature.	Plant will be stretched. Internodes are larger.
Low 24 hrs temperature.	Plant will be compact. Internodes are shorter.

At clear nights when there is a large radiation out of the greenhouse, the night temperature can be raised by 1°C. This will avoid too short plants with the first flower truss too low in position.

The perfect position of the first flower truss is between the 9th and 10th leaf. The height of the first truss is influenced by two factors: temperatures and the amount of light. The more light, the lower the first truss. A lower temperature during the first two weeks also results in a lower first truss. In the last case the evaporation might be insufficient, therefore water temperature in the pipes must be more than 50°C. This will stimulate evaporation but will also necessitate ventilation to maintain lower temperature.

When there is a lack of natural light, illumination is resulting in a stronger plant with shorter internodes. For practical reasons illumination is usually taking place before planting out, this way many plants can be illuminated with few lamps.

When using illumination it should be done max. 18 hours a day. The use of artificial light will also advance the planting date slightly. Tomato plants need a minimum of 6 hours darkness per 24 hrs. Start the night in a natural way, avoid sudden darkness when using illumination.

Carbon dioxide is taken by the stoma of the plants. It is given daily, starting several weeks after sowing. Normally CO₂ can be given from 1 hr after dusk to 1 hour before dawn. When there is enough light, CO₂ can be given from dawn till dusk. The most common method of distributing CO₂ is by injection of the heating fumes via perforated soft plastic tubes between the plant rows. Because CO₂ has more weight than the surrounding air, it will move towards the lower part of the greenhouse.

A condenser is cooling the CO₂ gasses emitted by the exhaust of the heating installation. Extra ventilators are needed to distribute the CO₂ through the greenhouse. The concentration in the glasshouse atmosphere is raised to 600 - 700 ppm (0.06 - 0.07%), about double the amount of the outside air. Regular checks with reliable equipment at the start of enrichment and periodic checks thereafter are required to ensure that satisfactory levels are maintained.

In general a cultivation should be started with a more vegetative balanced plant. A correct plant at the start of a crop has the following characteristics in general:

· the internodes should be correctly spaced (on average 5 - 7 cm, depending on variety);

Watering the seedlings shortly before transport from propagation can cause crispy plants, risking breaking of the young plants. Take extra care during the transportation of the seedlings. The plants are very sensitive to sudden changes in temperature and draft. Avoid contact with the outside air by covering the seedling trays with plastic during transport. It is preferred that the plants are transported standing up. Make good preparations in the greenhouse to make transplanting as quick and efficient as possible.

The structure of the greenhouse should be as weather tight as possible, in the interest of fuel economy and temperature maintenance. The greenhouse structure must be properly cleaned and disinfected. Spray the glasshouse roof and gables with clean water (possibly with added disinfecting) after cultivation. When producing in soil, disinfecting by steaming or use of methylbromide should take place.

Start heating the glasshouse one or two days before the plants arrive to make sure the temperature is correct when planting. The soil temperature should have a minimal level of 16°C.

The soil has to be leveled and structured. The soil could be covered with white plastic against weeds and to improve light reflection. Because of the light reflection, this measure will also have a generative effect on the plant. Covering only part of the soil with plastic will improve the humidity in the greenhouse.

Have the soil analyzed and take proper measures to have the correct nutrient level.

Make sure the greenhouse is ready to receive the plants. This means that the glass is cleaned, the structure is cleaned, the soil is disinfected and structured, the plant holes are ready and the irrigation is installed and properly working.

Planting can take place when the quality of the young plant is as indicated earlier. In the case of production in soil it is best to start planting directly after delivery. Make sure not to damage roots during planting. Keep the top of the block 1 or 2 cm above the soil level, so the glasshouse soil does not touch the stem of the plant, to prevent infections. After the plants have been planted, they should be watered with an E.C. of 3-5 mS, depending on the variety, the plant size and season. The plants must be watered from underneath to avoid burn damage on the foliage. This can be done by a hose or with drip irrigation.

It is important to have a good balance between vegetative and generative development of the plants. Make sure the roots do not grow too deep into the subsoil, resulting a too vegetative plant which is very hard to be controlled. This is usually achieved by watering the plants with a relative high salinity.

An average density for early crops is 2.4 plants per m². Main crops growing under better light conditions could be spaced at 2.25 - 2.50 plants per m². A standard spacing between two plant rows is 70 cms, and 90 cm between the walking paths. Within the rows plants are normally spaced between 50-55 cm.

It is common to take extra side shoots with a December planting. This is done when the 6th truss is in development. This will increase plant population when the light conditions are improving. In general a side shoot is being kept from every fourth plant. Use an extra thread of a different color to support the newly created head. When the light conditions are sufficient, another extra head can be created at the height of the 10th truss on the plant.

The head stem is twisted into the new thread, the side shoot will follow the old thread. This way both heads will grow at the same height.

Later in the season, when light conditions are deteriorating, the heads of the extra side shoots have to be removed. This way the plant density will be decreased.

Long season crops grow along a thick thread up to the iron wire (at a height of minimal 3 m.). At this height the plants should be fastened to the iron wire by means of a reel. Every time the heads of the plant reach the iron wire, the plants are lowered a bit and the main stem will be moved a little to one side by sliding the reel on the iron wire. Use new threads every year to avoid fungus infection.

The distance of the iron wires should be at least 80 cm in order to guarantee that sufficient light reaches the head of the plants. Fasten the plants on the thread under the 2nd or 3rd leaf. We recommend training the plants in an inclined way. The advantage is that the plants do not grow towards the middle of the path, which would damage the fruits when the harvesters pass by. When the plants grow inclined they will stay in their place and all the trusses hang to one side.

During the cultivation all the main stems will be lying on the soil, with a support under the stems. This support can be easily made by pricking iron wire "bridges" into the soil. This system of lowering the plants has a positive effect on the fruit quality (better coloring, cooler fruits in the summer) and makes to crop easier to work with.

In general the heads of the plants should be twisted into the thread once a week. Between two trusses the thread should be twisted one turn. At the same time the reel can be lowered. When twisting, make sure the plants are twisted not too tight and are that the heads are turned clockwise. When twisted counter clockwise, the plant will be obstructed by the thread when the head is following the movement of the sun.

Varieties with large fruits will benefit from truss support. This measure will prevent the first 8 clusters from bending and obstructing fruit development. There are several common supporting methods:

- the use of small nylon clips which are pushed on the cluster stem to prevent it from bending;

- scraping of the cluster stem with a knife. This will create callus tissue, creating a stronger stem;

- bending the cluster over a small round object (stick or pencil). This will also create callus tissue;

The temperature has a major effect on the plant growth and fruit development throughout the life of the crop. The number of flowers, fruit size, shape and color, together with the rate of growth and ripening are all strongly influenced. Therefore, the precise control of the temperature is essential. It is also very important to always maintain uniform conditions instead of large fluctuations of temperature, humidity, watering etc.

Night temperature:	16-18°C
Day temperature:	18-20°C
Soil temperature:	18°C (environmental temperature)

The 24-hour temperature must be correlated to the condition of the plant and the amount of light available. When the plant is too heavy, the 24-hour temperature should be higher. This measure should only be taken when there is sufficient light available, the temperature in the morning should be prolonged to reach the desired effect.

By using the temperature regime above, together with CO₂ enrichment, early planted crops can be expected to commence producing 8 weeks from planting. It is recommended to have 5 heating pipes of 51 mm diameter in a bay of 3.20 m; 4 below and 1 at a height of approx. 3m, in order to get a good air circulation within the greenhouse and also to prevent the attack of all kinds of mould. Ventilators will also help in obtaining a good air circulation. The high positioned pipe must be connected to a separate heating cycle to make it possible to regulate separately from the bottom pipes. This is very important because this high pipe will heat the heads of the plants, allowing the pollen to loosen, the fruits to color and to improve the evaporation of the plant.

The minimum temperature for both the lower and upper heating system is depending on the outside temperature. (generally speaking 35-55°C) When the lower part of the plant is relatively low in temperature compared to the head of the plant, pressure spots and cracks may occur in the fruits, caused by a too high root pressure. Always change temperatures gradually. When a plant is heated to quickly, cracks might occur in the fruits.

At the beginning of cultivation, it is a common method to us "pre-night temperatures". In this period of time between 18:00 - 24:00 hrs, the temperature will be lower than the temperature after 24:00 hrs. This measure will stimulate vegetative development of the plant, resulting in strong first clusters. When the head of the plants is too thin, several hours of low temperature in the pre-night will stimulate plant vigor. Do not lower the temperature below 15°C and lower the temperature gradually.

Lower temperatures in the pre-night will also have an effect on the fruitsize, fruits will be larger.

Too low temperatures in general will block the absorption of nutrients, stopping development of the plants. This is often visible by purple coloring on the stem or under surface of the leaves.

Routine watering begins immediately after planting. Water should be applied frequently in small quantities to maintain the moisture status. Watering is done underneath the crop. The best method is drip-irrigation for an even distribution of the water. When using furrows the distribution can easily be improved by using thin perforated plastic tubes with the end closed in the furrow. By connecting the watering hose to the one end, there will be a more even distribution all along the furrow.

Watering is done according to evaporation, sun radiation, soil structure, vigor of the crop, ventilation, etc. The grower himself has to make an adequate decision regarding the time and quantity of watering and fertilization. Always use water with a temperature above 15 - 16°C.

When watering the plants, the nutritive situation in the soil will be lowering very fast, especially nitrogen. Use clean, pure water as a base when irrigating. The use of rainwater is very common. Depending on analysis, nutrients are added to the water.

It is essential to keep the plants active and evaporating. Ventilation is very important to avoid a too high humidity and condensation on the plants, encouraging the development of many disorders, particularly Botrytis and Cladosporium. An optimal relative humidity is 65-75%. At this humidity fruit setting is optimal. Try to avoid relative humidities below 50%. This will cause the plants to become sturdy and fibery.

b) a minimum pipe temperature day and night. This is controlled by a thermostat in the return pipe and set at 30-45°C, the level depending on the weather conditions. As fuel is costly, pipe heat should only be used for humidity and disease control when a) is insufficient.

When ventilating, always open the windows on the opposite side of the wind direction. This way the "chimney effect" will result in a good ventilation of the greenhouse.

Wrong levels between calcium carbonate and pH might cause blossom end rot or blotchy ripening. Low levels of calcium carbonate and pH cause the susceptibility for blossom end rot. Blossom end rot might also occur when there is a low Ca-level and a too high salt concentration. High levels of Potassium (K) will also obstruct the absorption of Ca.

A low salt concentration in the soil causes blotchy ripening, especially with a high Ca-level. With the following levels, chalking is not necessary:

е	% Calcium carbonate	pH H₂O
Sand	0,3	6,2
Sandy clay	0,4	6,5
River clay	0,3	6,5
Sea clay	0,5	6,7
Clay with peat	0,2	6,3
Peat	-	5,5

When the pH and % calcium carbonate are lower than the mentioned figures, chalking is recommended. A calcium fertilizer which is often used is agricultural chalk.

The Fe and Al figures have to be low. High figures means that the pH of the soil is too low or that the relation between water and air in the soil is not good. When using farmyard manure, mind the evaporation of ammonia (NH₄), which causes damage to the plants. Farmyard manure must be kept moist and ventilated to avoid building up of ammonia.

Leaf fertilization is commonly used. In general Magnesium and Boron (Borax) are applied one a week. Use a fine mist when spraying the plants and spray over the heads of the plants. Borax will also have a good effect on the firmness of the trusses on the plant. Magnesium will help to avoid blossom end rot. Another popular leaf fertilizer is Algan. This product contains good levels of nitrogen and trace elements.

It is very important to have a constant balance between generative- and vegetative growth. When the plant is too generative, too much energy will be consumed by the fruits risking future production and yield. On the other hand, when the growth is too vegetative the plant will be too vigorous, resulting in a lower yield. The plants have to be in balance, active and assimilating continuously. This can be achieved by adjustment of temperature, humidity, ventilation, CO₂, light, fruits, foliage and available nutrients in the soil.

Pay close attention to the heads of the tomato plants at all times. The heads should have the correct thickness and shape and there should be a slight purple color present. This indicates that there is enough growing energy. At the beginning of the day the plants should be sturdy and the foliage should be erect. At the end of the day the foliage should be curled, indicating that the plant has been active all day. When the plant has not been active enough, the most common method is raising the temperature slightly in the afternoon to improve evaporation and to stimulate the plant.

In general a cultivation should be started with a vegetative plant. First a strong plant has to be created to form a good base for a balanced production. In general it can be said that a tomato plant has approx. 15 leaves and 7-8 trusses of tomatoes on the plant. The new development of one new cluster every week is a normal frequency. When the plant is developing correctly, there should be three leaves present between the trusses. The plant is most heavily loaded when truss 8 -11 is flowering. Avoid a too generative growth in this stage.

When a plant is out of balance, corrective measures should be taken. Always make slight adjustments and gradual changes. Within several days a reaction of the plant will be visible.

The following observations can be made when there is too much vegetative development:

2. Low fruit weight, taking into consideration the characteristics of the variety.

3. Head of the plant is too large. Position of upper flower cluster is too low, too much foliage above the cluster. Normally there are three leaves above the upper cluster, which is approx. 15 cm. (depending on the variety).

When the plant is growing too vegetative, the following measures will help to move the plantbalance towards a more generative growth:

1. Create a larger difference between day- and night temperature. Raise the temperature in the afternoon to stimulate the plant (up to 25°C when there is sufficient light available). Then lower the temperature towards 16-18°C in the pre-night. This change in temperature will stimulate generative development.

2. Lowering of the relative humidity. More ventilation and heating will lower the humidity and stimulate a more generative development of the plants. Do not lower the humidity below a level of 65% because this will risk poor pollination.

3. Removing of foliage. Besides the normal leave trimming at the bottom of the plant, a small leaf can be removed out of the head of the plant when the plant is too vegetative.

4. Less truss pruning. Allow more fruits to develop on the plant by keeping more flowers on the trusses. Prune at a later time when the fruits are small.

5. Increase of nutrient level in soil or substrate. A slightly higher E.C. will stimulate the generative development op the plants. Higher levels of Potassium (K ) will also have a positive effect on the fruit quality.

The following observations can be made when there is too much generative development:

2. High fruit weight, taking into consideration the characteristics of the variety.

3. Head of the plant is too thin and small. Position of upper flower cluster is too high, head above the upper cluster is less than approx. 15 cm (depending on variety).

When the plant is growing too generative, the following measures will help to move the plant balance towards a more vegetative growth:

1. Adjust temperature regime. Create a smaller difference between day- and night temperature and have a lower 24-hours average temperature. This measure will stimulate a more vegetative growth.

2. Raising the relative humidity to a maximum of 80 %. Less ventilation or watering the soil will cause a higher humidity, leading to a more vegetative growth. Pay attention that a higher humidity will also encourage the development of fungus diseases.

3. Truss pruning. This measure is very important. When there are too many fruits on the plant, the plant will not be able to fully develop all fruits and the plant will be too generative. Pruning takes place before the flowers are opened. To stimulate vegetative growth flower buds have to be removed. In general 5 or 6 flowers are left on the truss, depending on the variety. When more flowers are present, the smallest ones are clipped out by hand or with a pair of scissors. Do not prune the first three trusses. Also dip the pair of scissors regularly in milk to avoid virus infection.

4. Have a higher planting density. This can be achieved by keeping side shoots on the plant to create more heads. This measure will only be effective when a vegetative growth is anticipated.

5. Decrease of nutrient level in soil or substrate. A slightly lower E.C. will stimulate the root system and lead to more vegetative development op the plant. Make sure there is enough Nitrogen available to the plant.

To chalk the greenhouse will block part of the radiation from the sun. This will also have a vegetative effect on the plants. However, to apply chalk as a reaction on an excessive generative growth should only be done when other measures will have not enough effect.

The glass can be chalked to avoid excessive temperatures inside the greenhouse during the summer. This method should only be used with excessive radiation and when abundant ventilation is not sufficient to lower the temperature, because any reduction in light tends to reduce crop yield.

Remark: Never chalk the whole greenhouse. When producing summer crops in hot climates, a good method of chalking is to only chalk the south-sides of the top construction and the lower two meters of the side construction. This way the intense radiation of the mid-day sun will be blocked, while there is enough light entering the greenhouse in the morning and afternoon.

Side shoots should be removed and the heads of the plants should be twisted into the thread once a week. Do not twist the plants when the head is relatively small. Make sure to twist the plants clockwise, to avoid "strangling" of the plants when the heads of the plants move with the direction of the sun.

When removing side shoots, make sure the complete side shoot is removed, avoiding the risk of Botrytis infection.

Early in the season old and damaged foliage low down on the plant should be removed to improve air circulation and reduce the risk of Botrytis inflection. A normal frequency of trimming is between 2 - 3 leaves/week.

The following guideline can be used: When the first cluster is being harvested, the foliage should be removed up to the second truss. This way the clusters will be clearly visible and will not be in the shadow. In general there should always be a minimum of 15 leaves on the plant to assure good assimilation and growth.

The best time to remove the leaves is early in the morning when the water tension in the cells is rather high, so that the leaves break quickly. Another advantage of removing leaves in the morning is that the wound will have time to dry during the daytime and fungus infection will be avoided.

The leaves are removed upwards in order to leave the smallest wounds. When the leaves do not break easily, a knife should be used. When using knives make sure to disinfect the knife with milk avoiding virus infection.

Later heavier trimming is sometimes necessary (to stimulate generative growth), but even then every effort should be made to retain the maximum amount of healthy foliage, certainly not less than the top 1.5 m of the stem.

Do not leave cut leaves and side shoots in the greenhouse. This foliage should be collected and taken away. Old and dead plant material left on the soil can be a source of infection, especially of fungal diseases.

The normal outside CO₂ concentration is approx. 340 ppm. Without ventilation the normal carbondioxide concentration will decrease in the greenhouse, because of absorption by the plants via the stoma. Carbondioxide is also emitted by organic soil material but insufficient to the plant's needs. A too low CO₂ concentration in the greenhouse will lead to an interrupted growth.

More ventilation will help to increase the CO₂ concentration. However, the optimum concentration is 800 - 1000 ppm, which can only be achieved by artificial dosing. This is usually done by recycling fumes of the heater through a condenser. The CO₂ absorption of an active tomato crop can be as much as 50 kg/hr/ha, which is released when burning 25 m³ natural gas. Use a good CO₂ meter to measure the concentration.

Be careful with incomplete burning of gas as this results in the release of a/o. CO and Ethylene. A CO detector is a good investment to prevent CO en Ethylene damage. Have the heater checked and adjusted regularly, at least once a year.

CO₂ is given daily, starting several days after planting, from one hour after dawn till one hour before dusk. Carbondioxide is needed most on moments with high radiation.

The weather conditions should be taken into consideration when injecting CO₂. With calm weather a higher than average concentration should be expected and a lower than average level with windy conditions. Note that ventilation is more important than CO₂ injection! Opening the windows one cm on the opposite site of the wind direction will cause enough ventilation to allow new CO₂ to enter the glasshouse.

The use of isolated warm water storage tanks is a very common method in the Netherlands. This way CO₂ will be produced during the daytime by heating water with natural gas. The hot water will be stored in water tanks to be used during night-time when heating is required. This system is also saving energy because the heater capacity is used in the most optimal way.

In general truss pruning is necessary to maintain a good balance in the plants. The remaining tomatoes will be larger and more uniform. In general the following rule can be applied: The first and second truss should be pruned to 5 fruits, the rest of the trusses should have 6 fruits.

The development of flowers take a lot of energy of the plant. Therefore truss pruning should be done when the flower cluster is still small and the flowers are not fully developed yet. This is very precise labor and should be done by dedicated personnel.

The first flower on a truss can become a "king fruit". These flowers must be removed. When more king fruits appear, the growth is too vegetative. This disorder can also be the result of a sudden temperature drop during the plant raising phase. Remove poor pollinated fruits.

Damping cools the plant under very hot conditions, reduces the moisture stress and prevents a too high evaporation. Damping could be done on bright sunny days when the relative humidity is becoming too low. Spray by hand over the heads of the plants. Spray with large droplets to stimulate pollination as well. Timing should permit the plants to dry off before dusk. Damping should be continued as long as possible, but should cease if fungal diseases are becoming a problem.

The time from fruit set to harvesting the fruit in the spring takes about 55-60 days. After the pollen has reached the pistil it takes 3-5 hours for the pollination to take place. Total time of development from flower to ripe tomato is approx. 8 weeks.

The best conditions for the fruits to be pollinated is at a temperature of 25°C with a humidity of 65 - 75%. Pollination can be achieved by the following methods:

The most effective system is the use of bumblebees for pollination. When using vibrators, all flowers should be touched with a vibrating pin to release the pollen. Vibration is usually done 2-3 times a week, usually right after having harvested in the morning. Vibrating the plant via water droplets is also possible but the use of vibrators is preferred. When spraying use water with a minimum temp. of 16°C and spray over the heads with relative large droplets.

Hormones should only be used when the circumstances in the greenhouse are not good enough for the pollen to be released. The most common used hormone is Chlorofenoxyacetil acid (Tomatone) at a dose of 2% per 10 liters of water. This quantity will treat approx. 1000 - 1500 trusses. Do not drench the whole flower truss into the solution on avoid contact with the foliage. The best method is to use a small hand sprayer and to hold the flower truss in front of the hand palm when applying the hormone solution.

It is useful to pick the fruits 3 to 4 times a week. Always do this in the morning, because at that time the fruits have the highest weight and the best quality. When harvesting early in the year the fruits can be harvested when there is a little bit of color present. In spring and autumn the ripening of the fruit is slower, therefore the fruits should be harvested in a more red stage than during the summer.

Use boxes or baskets with some foamy plastic or rubber on the inside to prevent damage of the fruit. If possible put the boxes on a small cart, which is easier when harvesting and causes less damage to the fruit. The optimum storing temperature is 12-13°C.

It is highly recommended to use several "diagnosis-plants" in the greenhouse. Make regular measurements of the plant size and record how much leaf has been trimmed and how many clusters have been harvested. Also, when applying corrective measures never apply these on the entire greenhouse at once. First try part of the greenhouse to check the effect of the measure.

2. Length of the foliage. Measure the length of the foliage under the flowering truss.

4. Number of fruits on the plant. Record both the fruits harvested and the fruits present on the plant.

When problems are occurring, records of temperature, humidity, ventilation, watergift etc. can be compared to the development of the plant. This way the cause of possible problems can be tracked and the grower will have a better understanding of the problem which occurred.

Number the paths and keep track of the spots were diseases do occur. Also involve the personnel by giving them information about possible problems and stimulate them to report problems!

When the end of the cultivation is approaching, it is usual to remove the growing point 2 leaves above the uppermost flower truss. The head is removed at least 7 weeks before the anticipated date for removal of the crop.

After the head has been removed, the plants need to be twisted into the thread once more. At the same time the side shoots have to be removed. The following weeks the head should not be touched. The emerging side shoots are needed to keep the plant active and to create a sap stream. After several weeks, most of the side shoots can be cut out of the head. Always leave a side shoot in the head of the plant, to stimulate the sap stream. When this side shoot is large enough it should be removed except for two leaves. Above the highest truss there should always be two leaves and a side shoot present.

5 to 10 days before the last harvest, it is possible to paint part of the stem with Ethylene. This hormone causes fast ripening of all the remaining fruits on the plant.

After last fruits have been harvested, take the remaining plant material out of the greenhouse. The structure should be cleaned, the soil should be disinfected and preparations can be made for the cultivation of the next crop.

The object of the following description is to supply basic information about growing tomatoes in soil. We did not have the intention to be complete but want to supply some guidance that may serve as a supplement to the practical knowledge of the grower.

The information provide is based upon Dutch experience with growing tomatoes. Although this leaflet is written according to the most recent information available, we do not accept any responsibility if the expected results are not achieved. Furthermore we do not guarantee the same results in all environmental conditions. Growing anywhere else in the world may well necessitate a different interpretation.

In general, sowing is done in trays with rockwool plugs. When the plants are large enough to be handled, usually after 10-12 days, the seedlings can be transplanted. When planting rockwool plugs it is common to plant the plugs upside down in the blocks. This way the plant will be shorter and more erect. Also the stem of the seedling will be more into contact with the block, resulting in extra roots and a stronger plant. Do not water the plugs one day before transplanting to avoid crisp, fragile plants with the risk of breaking.

The irrigation water, which usually contains a certain number of elements, is subject to high quality standards. First of all the sodium and chloride contents need to be defined, as well as the E.C. Also, the contents of magnesium, calcium, zinc, iron, and bicarbonate (in connection with the pH) can be of importance. For the valuation of the irrigation water two standards can be used. The first standard more or less implies an ideal situation, while the second standard involves necessary adaptations. Exceeding standard 2 means that the use of the irrigation water will have a negative influence on the crop. For that reason the water should not be used as irrigation water for cultivation on rock wool. The following table is defining these standards.

Determination	Standard 1 (good)	Standard 2 (suitable)	Not suitable
E.C. in mS/cms	< 0,5	< 1,0	> 1,0
Cl in mmol/l	< 1,5	< 3,0	> 3,0
in mg/l	< 50	< 100	> 100
Na in mmol/l	< 1,5	< 3,0	> 3,0
in mg/l	< 30	< 60	> 60

The use of water with higher sodium and chloride contents may result in yield reduction. Moreover, too much nutrient solution would have to be used to rinse the slab in order to prevent a too high salt accumulation, resulting in high fertilizer losses. The use of water containing bicarbonate (HCO_3-) will eventually result in increased pH levels in the slab. This can be neutralized by using saltpetre or phosphoric acid. The higher the bicarbonate concentration, the more acid must be added. The total iron figure (Fe) is not important in connection with feeding the plant, but it is in connection with the drip system becoming filthy and clogged. Ferruginous water cannot be used unless the iron is properly removed. If the iron present deposits easily, even a quantity of less than 0.5 milligram per liter may cause blockage of the drip system.

From a plant nutrient point of view the total iron content could be higher because the form in which the iron is present in the irrigation water makes it practically unavailable to the plant (contrary to the soluble iron which is determined in feeding solutions).

The quantities of various elements may vary considerably. In case the quantities exceed the upper limit, extra rinsing during cultivation will be necessary. Too high contents may result in excess phenomena. According to the required standards for the water, most nurseries need rainwater (stored in reservoirs) or desalinated water (by reversed osmosis). Only a few nurseries have ground water or open water of an acceptable quality. An extensive analysis of the irrigation water is necessary to determine its suitability or to adapt the composition of the nutrient solution to the particular salt contents of the irrigation water.

Rockwool contains practically no nutritious matter, therefore continuous dripping with a nutrient solution is required. The growing system which is practiced here does not affect the composition of the feeding solutions, provided that the drain water is not re-circulated but allowed to drain freely from the slabs. The basic composition of the nutrient solution is as follows:

Macro (main) elements	Quantity
NO₃^-	13.5 mmol/l
H₂PO₄^-	2.0 mmol/l
SO₄^-	3.5 mmol/l
NH₄⁺	0.5 mmol/l
K⁺	9.5 mmol/l
Ca⁺⁺	4.75 mmol/l
Mg⁺⁺	1.5 mmol/l
Fe	20-25 µmmol/l
Mn	10 µmmol/l
Zn	5 µmmol/l
B	25 µmmol/l
Cu	0.75 µmmol/l
Mo	0.5 µmmol/l

Generally, the nutrient solution in the table above is prepared out of two concentrated stock-solutions, called A and B, which can be dosed into the irrigation water. It is not possible to mix these solutions in concentrated form as this will result in a deposit of calcium sulphate or calcium phosphate, which will clog the irrigation system.

The composition of the feeding solution in the substrate does not always have to be equal to that of the basic composition. Dosage of ions which can be taken up more easily by the plant may occur in the substrate in lower concentrations than in the basic composition.

As for the feeding ions which are more difficult for the plant to absorb, the contents in the substrate have to be higher. In the following table a survey is given of the analysis figures in the slab. This is a general guideline. In this table the limits in between which the contents may vary are also mentioned.

Strive figures and limits for the analysis results of the feeding solution in the rockwool slabs:

Measurements		Strive figures	Limits
Е.С.	mS/cm	3.5 – 5.0	2.5 – 5.0
pН	mS/cm	5.5	5.0 – 6.0
NH₄⁺	mmol/l	0.5	0.1 – 0.5
K⁺	mmol/l	7.0	6.0 – 9.0
Na⁺	mmol/l	6.0	1.0 – 6.0
Ca⁺	mmol/l	7.0	6.0 – 9.0
Mg⁺⁺	mmol/l	3.0	2.0 – 4.0
NO₃^-	mmol/l	16.0	12.0 – 20.0
Cl^-	mmol/l	6.0	1.0 – 6.0
SO₄^-	mmol/l	4.5	3.0 – 6.0
HCO₃^-	mmol/l	1.0	0.1 – 1.0
P	mmol/l	1.5	1.0 – 2.0
Fe	µmmol/l	15.0	9.0 – 25.0
Mn	µmmol/l	7.0	3.0 – 15.0
Zn	µmmol/l	7.0	5.0 – 15.0
B	µmmol/l	50.0	40.0 – 70.0
Cu	µmmol/l	0.7	0.4 – 1.5

The absorption by the crop and the accumulation and consequent rinsing of salts, submits the nutrition level in the slab to strong fluctuations. Accordingly the following remarks can be made:

The Electric Conductivity is measured in mS/cm at 25°C. This value of the nutrient solution in the slab is the most important data to know. Based upon this, the concentration of the irrigation water is regulated. It is advisable to irrigate the slab before planting with an E.C. of about 2.2. During the cultivation the level in the slab is in general varying from 3.5 - 5 . This implies that the E.C. value of the irrigation water should between 2 and 3.

The following can be considered a general guideline: The sum of the E.C. values in the slab and of the water should be equal to 6 mS/cm.

During the autumn and winter months and during the start of a new cultivation in summer it is advisable to stick to a somewhat higher E.C. level in the irrigation water. A slightly higher E.C. will stimulate the generative growth and also result in better fruit quality. Continuous dripping with low level E.C. irrigation water may almost certainly result in an insufficient nutrient level in the slab, thus resulting in backward growth and poor fruit quality.

Furthermore, it is advisable to raise the E.C. value in the slab gradually, preferably not exceeding 0.5 E.C. at a time. Especially during the winter months (low light intensity) a sudden rise in the E.C. value would cause root burning. Wide fluctuation in the E.C. value must be prevented. Regular application of nutrient solution is to be preferred.

During the day, the E.C. can be slightly dropped later in the morning because the plant is evaporating more and need more water with a low E.C. After removal of the head of the plant (8 weeks before the end of production) the E.C. of the mat can be slowly raised.

During the plant raising period, generative varieties could be standing in a slab E.C. of 2.5. The weight of the plant should be carefully monitored. When the E.C. is getting higher the plant will be more generative in development, which might be needed when growing certain varieties. Do not exceed an E.C. level higher than 5-6.

Chloride has a good effect on the firmness of the fruits. However, the chloride concentration in the slab has to be kept rather low. Above 6 mmol chloride per liter it is advisable to add extra nutrient solution to leach the slab a little (10 - 15% extra).

Excessive levels of Natrium will shorten the shelf life of the harvested fruits. Therefore the Na level has to be kept as low as possible. Calcium has a strong effect on the salinity (E.C.) value of the solution. With Na levels above 6 mmol/l, difficulties with the absorption of K and Ca will occur.

The optimal pH in the slab lies around 5.0 - 6.0. The pH of the water should never be lower than 5.3 to avoid instability of the water. The following will occur when the pH level is not correct: