Everything you need to learn about the cultivation, production and growth of tomatoes in greenhouse!
Among vegetables, tomato is the first crop grown in greenhouses worldwide. It is relatively easy to grow compared to peppers and cucumbers, and fruit yield can be very high under protection. Demand for tomatoes is usually strong due to the vine-ripe nature and general overall high level of eating quality.
There are two main types of tomato viz.:
(i) Determinate or ‘bush’ tomato, and
(ii) Indeterminate or ‘vine’ tomato.
Determinate cultivars are used mainly for processed food while indeterminate cultivars have been largely developed for greenhouse systems.
Climate Requirement for Tomato Cultivation:
Tomato is a warm season plant. It cannot withstand with severe frost conditions. Temperature and light intensity affect germination, vegetative growth, fruit set, pigmentation and nutritive value of the fruits. The minimum temperature for germination of seeds range from 8° to 10°C.
The night temperature is the critical factor in fruit setting with the optimum range of 16°C to 22°C. Fruits fail to set at 12°C or below. Fruit set is also reduced markedly when average maximum day temperature goes above 32°C and average minimum night temperature goes above 22°C. However, now some cultivars are available which can set fruit beyond the critical temperature limits and are called hot set and cold set cultivars, respectively.
At low temperature i.e. below 10°C, red and yellow colour do not develop. The ideal range for development of both red and yellow colour is 18-25°C. Under greenhouse conditions tomato crop can be grown for long duration (10-12 months) by cooling during summer months (April to June or July) and by heating the greenhouses during peak winter months (December and January) in northern parts of the country.
Selection of Varieties for Tomato Cultivation:
Selection of the most suitable cultivar is a pre-requisite for successful tomato cultivation in a greenhouse. The important characteristics related to cultivars include high yield, freedom from cracking, disease resistance, high percentage of number of fruits, freedom from green shoulder, good shelf life and TSS. Consumer’s preference with respect to size, shape and colour of the variety also plays an important role in varietal selection.
Greenhouse tomato cultivars are indeterminate in growth habit (produce flowers and fruits continuously along the main stem as it grows). As a result, plants may reach a length of 30 to 40 feet in 10-11 months duration of cultivation.
Modern tomato cultivars/hybrids are resistant to diseases than old open-pollinated varieties. Hybrids have almost replaced open-pollinated cultivars in most tomato producing centers of the world over. For tomato cultivars to perform well, they must have ability to variable conditions of winter and summer season, and have freedom from russet and other cracking disorders.
Tomatoes grown in the greenhouses are generally separated into the following four categories:
(i) Beefsteak Cultivars:
Cultivars of the beefsteak category produce large (180 to 250 g) slicing type fruits. The fruits are harvested individually and usually packed with the calyx attached. Beefsteak cultivars are being used in nearly all European countries and USA for greenhouse production. However, since 1990 a few growers began to produce cluster types. The most popular US cultivars currently grown are ‘Trust’ and ‘Match’.
These are high yielding and non-green-back (non- green-shoulder) cultivars that produce large and uniform fruits. Both cultivars are somewhat susceptible to russeting or fruit crazing. Russeting is a disorder causing very small cracks on the surface of fruits near maturity. Wide fluctuations in temperature and moisture in the greenhouse must be controlled to reduce russeting. The important and popular varieties in this group are FA-574, FA-180 and FA-514.
(ii) Big Fruited Varieties:
Several tomato varieties have been developed for greenhouse cultivation in Europe, USA and Israel, but in India only few varieties are available, which can be grown in greenhouses for long period cultivation. Israeli varieties are quite suitable for cultivation under Indian conditions and particularly in northern parts of the country.
The average fruit weight under this group ranges from 120-160 g per fruit. The important Israeli big size tomato varieties for greenhouse cultivation are R-144 (Daniela), FA-189 and FA-179 which is very high yielder and produces high quality fruits with an average fruit weight of 120-150 g.
Some Indian varieties from public and private sector suitable for greenhouse cultivation are Naveen, Nun 7711, N.S. 646, GS-600, Arka Vardan, Arka Vishal, Delphi, Astona, Cronos, Shanmon and Cassius. The fruits of this category are also harvested singly with the calyx attached.
(iii) Hand Type or Cluster Type:
These varieties produce small fruits and are harvested in clusters of four to seven fruits with the cluster stem still attached, which is an indicator of freshness of the fruits for the consumers. The clusters are harvested by clipping the main cluster stem from the plant. All tomatoes in the cluster remain attached and range in maturity from breaker to ripe. The harvested clusters are usually marketed in a mesh bag, tray pack, or in a single-layer box.
Many cluster tomato cultivars like HA-646, FA-556 and FA-521 have outstanding flavour and appearance to compete with the best of the field vine-ripe tomatoes. In addition, consumers are attracted to the tomato aroma provided by the stems of the cluster.
The consumers also enjoy harvesting of the fruits from the cluster themselves. Outstanding fruit quality and shelf life allow the consumer to pick tomatoes from the cluster over several days. The post-harvest quality of the calyx is, therefore, an important characteristic in the appearance of the cluster.
(iv) Cherry Tomato:
Another category of varieties is cherry tomato, which are very small in size and the average fruit weight is 12-20 g depending upon the variety. The cherry tomato varieties have high TSS (6.8 to 7.0 per cent). Among the cherry tomatoes, BR-124 and HA-818 varieties from Israel are most popular. Variety T-56, NS Cherry-1 and NS Cherry-2 are available in India, but the fruits of T-56 are little bigger in size. Otherwise this variety can be grown under both open field and greenhouse conditions.
Preparation of Soil, Nursery Raising and Planting for Growing Tomatoes:
In north Indian plains, the tomato crop is planted from first August to second week of September under greenhouse conditions. This crop is continued up to June or July under climate controlled greenhouse. If the greenhouse is naturally ventilated then the crop can be grown up to April or May months.
Nursery for greenhouse tomato is raised under protected structure, mostly, in soil less media in plastic trays to produce disease free and mainly virus free seedlings. The seedlings are ready for transplanting within 28-30 days under soil-less media in greenhouse or under other protected structures.
An average of 3 to 3.5 square feet area is provided to each plant. Healthy seedlings are transplanted at a planting distance of 60 × 50 cm, mostly, under drip irrigation system for efficient use of water and fertilizers for long duration cultivation of tomato crop. The low pressure drip irrigation system can also be used for greenhouse tomato cultivation.
Before transplanting of seedlings, soil is thoroughly prepared and beds are made with the help of tractor rotavator, and two drip lines of 20: 2: 50 sizes (20 mm diameter of laterals, 2 litre water discharge per dripper per hour and 50 cm distance between two drippers) are laid on each bed at 60 cm spacing. Transplanting is, preferably, done in the afternoon or at evening time for better establishment of the seedlings.
Early Season Care:
Immediately following transplanting, efforts are directed at monitoring plant establishment and controlling the environment of the greenhouse to maximize plant growth. Greenhouse shading is very important and fans should be set to maintain 85 to 90°F temperature. After seedlings have become established, the nutrient solution is changed to the first solution level for new plants. There should be frequent checking of plants for insect pests and diseases.
Training and Pruning of Grown Tomatoes:
Since greenhouse grown tomatoes are indeterminate in growth habit, therefore they need regular training and pruning right from the few days after transplanting. Single main stem should be retained in these tomatoes by removing all the side shoots or suckers that develop between leaf petiole and the stem.
Usually, in early stage the shoots are removed by snapping them off, avoiding cutting with knife, blade or scissors, as diseases especially the virus (TMV) can be transmitted from one plant to other. Plants are supported by plastic or binder twine, loosely anchored on the base of plants with the help of plastic clips or directly by non-slip loop and to overhead support wires (11 to 12 gauge) running to the length of the row of the bed.
Overhead wires are fixed normally 8 to 9 feet above the surface of the bed and are anchored firmly to the support structure. Twine should be wrapped clockwise around the vine as it develops with one complete swirl every three leaves. The vine should be supported by the twine under the leaves, not the stems of the flower truss or fruit clusters.
The twine is not wrapped around the growing tip otherwise the tip may break. When the plants reached overhead supporting wires, untie the twine (or take down the twine) from the twine roll after unlocking it to take down the vines at least 2 to 3 feet at every 15-20 days gap.
Vines with twines are moved in one direction with twine roll in one row on the overhead wires and in opposite direction in the adjacent row. The plants must be pruned and trellised on regular basis for 10-11 months life cycle of the tomato crop. The plants, thus, are 30-35 feet longer in their 10-11 months life cycle of cultivation. Clearly, the greenhouse will not be able to accommodate the plants vertically.
As fruits mature on the lower parts of the vines, pinch off older leaves below the fruits. This will provide air circulation, which helps to reduce the incidence of the diseases and opens the vines up for spraying and harvesting. Removal of excess fruits will also result in larger tomatoes at harvest that can fetch good price.
These tomatoes require pruning of all lateral branches as they develop to encourage a single leader. Pruning helps in overall management of the long-term tomato crop. Pruning must be done on a frequent schedule (every 3 to 4 days) so that only small side shoots are removed.
Excessive intervals result in large shoots that are difficult to remove causing serious damage to the plant and increasing the likelihood of diseases. Pruning is done early in the day when plants are turgid but dry. Suckers snap out of the leaf axils easily, resulting in a clean wound that heals easily. Care should be taken to remove only suckers and not the main terminal bud.
During sucker pruning, any leafiness in the flower cluster should also be pinched out. The pruning time should be used to inspect plants for obvious problems such as disease, nutritional deficiencies, insects, etc. All pruned plant material should be placed in a container and removed from the greenhouse.
Cluster Thinning of Tomatoes:
Tomato produces from one to about 10 flowers per flower cluster. Under good pollination conditions, about 6 to 8 of these flowers might form fruits. For many cultivars, especially large fruited cultivars, this number is quite large to develop properly. If too many fruits are allowed to set on a cluster, fruit size, shape, quality and uniformity are sacrificed.
Therefore, tomato clusters should be thinned to provide an optimum number of fruits per cluster. Cultivars with indeterminate fruit size are thinned to four or five fruits. Clusters should be thinned to the lower number of fruits during winter season. The small fruited ‘cluster’ tomatoes may not need thinning.
Cluster pruning should be done once a week. This allows several fruits in a cluster to set so that a choice can be made regarding removal and retention. The objective should be to thin the cluster to a group of fruits that are most uniform in size and age. Cracked and misshapen fruits should also be removed.
During cluster thinning the workers must be sure to take care not to rub or scratch fruits to be left. Small abrasions early in fruit development result in large scars at harvest. It is good to check clusters a week or two later to remove any small fruits that developed since the previous thinning.
Root and Leaf Pruning of Tomato Plants:
In addition to side shoot pruning, tomato plants require leaf pruning and if grown in the NFT system, some root pruning. The root pruning is done in the channel or tube discharge end. Roots will grow into the return system and may clog it if not removed. Roots should be trimmed back, away from the discharge end of the growing channels.
Leaf pruning is required to remove old leaves from the lower part of the plant to improve air movement under the plants and to make the growing plants easier to manage. It is done in conjunction to ‘leaning and lowering’ of the plants. As the plant grows, it soon reaches the trellis cable.
At this time, the plant needs to be lowered so that it can be maintained within the trellis system. Prior to leaning and lowering about 4 to 6 of the oldest leaves are removed. It is preferable to clip or hand-snap the leaves from the plant, leaving a clean, smooth wound that will dry and heal fast.
It is important that fleshy stubs or large wound do not result because these are ideal areas for disease organism attack. After pruning the leaves, the plant is loosened from its cable clip or tie and dropped down allowing new twine to dispense from the ribbon.
The plant is lowered so that there is an 8 to 10 inch air space between the floor of the greenhouse and lowest leaves on the plant. Usually, this results in lowering the plant 18 to 24 inches. The plant is re-clipped at the cable. During leaf pruning, the workers must ensure that no damage occurs to the stems. In addition, fruits should not be punctured by stems when these are lowered.
Pollination in Tomatoes:
Although tomato is highly self-pollinated crop, but aided pollination is needed in the greenhouse grown tomatoes due to limited air movement and high humidity. In several countries, bumble bees are being used as a pollinator for the greenhouse tomato crop. Bumble bees are the perfect pollinators, even under environmental stress conditions viz., low and high temperature.
Bee hives are usually active for 6 to 10 weeks where after these should be replaced. But in several countries an electric or battery-powered vibrators are being used to vibrate flower clusters above the area where they originate from the stem. The vibration will release sufficient pollens necessary for pollination.
Flower clusters are vibrated or shaken for a second or two with some sort of electric vibrator. This method is not effective on cloudy days because the humidity prevents pollen dehiscence even with vibration. However, it might be a good idea to pollinate on every sunny day during winter season.
This practice is done twice a day at 10:00 to 11.00 AM and 2.00 to 3.00 PM. Greenhouse humidity is lower at this time thus facilitating pollen dehiscence. In addition, fruit size seems to be maximized by pollination during these hours. This is probably related to the increased amount of pollen available during these hours.
While pollinating a cluster, one should avoid touching, developing fruits as even the slightest scrap can result in a serious fruit scar as the fruit enlarges. Air from a mist blower also has been found effective in pollinating tomatoes inside the protected structures. If tobacco mosaic virus (TMV) has been a problem the vibrator should be wiped after each use with a clean cloth.
Fertigation in Tomatoes:
Greenhouse tomato require large amount of water, particularly, during peak growing period. Tomato is sensitive to water stress during flower formation and fruit enlargement. Severe stress, resulting from applying water to meet 25 per cent of the evaporative water demand reduced the fruit set by 65 per cent while full water supply delayed flower initiation and reduced the flowering and fruit setting rates as well as flower and fruit number per truss.
Although, tomato require large amount of water it is also extremely sensitive to flood damage. If tomato roots are flooded (even if only for a few hours) damage to roots occurs and infection by the Pythium root rot organism is possible. One of the keys to successful irrigation management is correct timing of water application. The volume and frequency of application change with the season.
Mostly, fertilizers are applied with irrigation water through drip irrigation system for efficient use of water and fertilizers. Tomato crop require close attention to fertilizer programme so that high yield of high quality can be harvested. Optimum N supply is critical for the tomato but excess N may lead to excessive vegetative growth and delayed maturity.
Fertigation is mostly done @ 6.0 m3 per 1000 m2 area at an interval of 6-8 days during September, October and November after that the interval of fertigation is again increased and it is done at an interval of 10-12 days and further reduced from 6-8 days to twice a week during May and June months.
Fertilizer solution of 5: 3: 6 ratio of N: P: K can be applied through drip irrigation @ 5-8 litre solution per m3 of water according to growth and season of the crop. Nutrient uptake is continuous during the entire growth and development period of the tomato crop. If the nutrient availability in the soil is high, the plants need can met through root absorption during the entire growing period.
However, if the soil nutrient availability is limited, the requirement for fruit development will be a function of translocation from vegetative portions in combination with root uptake. Limited uptake of calcium due to drought or other reasons causes deficiency that cannot be compensated by translocation resulting in blossom-end-rot in fruits.
For correction of the calcium deficiency, calcium nitrate is also mixed in the fertilizer solution. But, care should be taken while mixing the fertilizers because calcium nitrate with phosphorus containing fertilizers can result in insoluble calcium phosphate. In addition, calcium sulphate can precipitate when calcium nitrate is mixed with magnesium sulfate.
To avoid these problems, one stock solution is prepared with calcium nitrate and chelated iron and the remaining materials are mixed in a second stock (or tank) solution. Micro-nutrients, especially magnesium (Mg), iron (Fe) and zinc (Zn) deficiencies are encountered in long duration intensive cultivation of tomato in protected conditions for several years. Therefore, these are also required to be supplemented.
Cooling, Heating and Ventilation for Growing Tomatoes:
Tomatoes grow and yield best when night temperature is 16 to 22°C and day temperature is about 26 to 30°C. For economic reasons, maintaining the night temperature at 18°C is best. At this temperature the grey leaf mold disease is reduced, and tomato yield and fruit ripening are satisfactory. Night temperature should not be allowed to drop below 15°C.
Because at low temperature, grey leaf mold is favoured and blotchy ripening is prevalent. Tomatoes perform best when temperature regimes are uniformly controlled. Wide fluctuation in temperature disturbs the growth rate and, eventually, gives rise to poor fruit shape, colour and enhances fruit cracking.
Most of the climate controlled greenhouses have evaporative cooling system. In north Indian plains, cooling is done from September to October and April to June. Ventilation and cooling is needed for tomatoes to reduce heat scalding on fruits. Evaporative cooling system is quite effective when the relative humidity in the atmosphere is below 40 per cent.
The majority of cooling on warm, dry days is achieved by exhaust fans and evaporative cooling pads. Heating of the greenhouses can be done from 15th December to January end to increase the temperature of the greenhouse during nights, so that the temperature cannot fall below 14°C. Heating of the greenhouse can be done with the help of electric operated heaters.
The heaters must be operated correctly and ventilated properly. Improper operation can waste fuel and incomplete burning can produce ethylene gas which may severely damage tomato fruits. The key for successful tomato production is to begin heating and cooling on a timely basis. Heating and cooling of the greenhouse is required when tomato is grown for 10-12 months duration.
Ventilation of the tomato house is still required on most days during winter season. During December, January and part of February, the cooling pad can be closed off. The shutter vents are then opened by thermostat or controller just before the first fan comes on. Cool air from outside is drawn in through the vents rather than the cooling pad. The cool air should be drawn in over the top of the crop, instead of directly onto the crop, in case cooling pad are used.
Carbon Dioxide (CO2) Enrichment for Producing Tomatoes:
The use of CO2 on tomato crop began in the early 1960s and currently, CO2 enrichment is routinely used on commercial basis. The raising of CO2 level from the normal ambient level of 350 ppm to 1000 ppm increases plant vigour and early fruit production and may, partly, compensate for poor light conditions.
The beneficial effects of CO2 enrichment are more evident when air temperature is on the high side and is proportional to the duration of the enrichment. Apply CO2 during the day or any part of the night when artificial light is supplied. The effective use of this technology requires that houses should be closed for long period each day.
Harvesting and Post-Harvest Handling of Tomatoes:
Harvesting of tomato fruits is a continual process throughout the growing cycle. Generally, most of the varieties are ready for first picking in 75 to 85 days after transplanting. Big size tomato (slicing tomato) fruits are harvested singly with attached calyx, graded and packed according to grades. During the summer months harvesting should be done in the early morning or late in the evening to avoid post-harvest losses.
Cherry tomatoes are mostly harvested with stems attached or sometimes singly with attached calyx with the fruits and are packed in containers of 400-500 g capacity. Fruits are always harvested with the help of scissor at full mature (ripen) stage. Fruits are graded according to the market requirements.
On the whole, 250 to 300 tonnes of big fruited tomatoes and 100-150 tonnes of cherry tomatoes can be harvested from one hectare greenhouse cultivated area. Fruit yield of tomato under glasshouse cultivation in European countries like Netherlands is very high (400-500 t/ha); whereas yield levels in countries like Israel, Turkey, Morocco under greenhouse conditions ranges from 300-400 tonnes per hectare.
Tomato Plant Protection:
Greenhouses are designed in such a way that as far as possible insect and disease problems are minimized or eliminated so that crop can be grown pesticide free. Generally, all four sides of greenhouses are covered with insect proof nylon net (anti-virus nets) of 40 to 50 mesh size to prevent insects, including white flies, thrips, aphids, etc. Preventing insects from entering the protected structures is the best way of controlling virus and insect problems.
However, if required, one or two sprays of insecticides can be done as and when needed. One spray of metasystox @ 1.5 ml per litre of water is done 10 days after transplanting. In case of mite’s problem, spray dicofol @ 2.0 ml per litre of water. Sometimes, if white flies or thrips have entered in the greenhouse, yellow and blue trappers can be used for trapping of such insects.
For the control of root knot nematode and other soil borne pathogens, soil sterilization is most effective and it is done by applying the formaldehyde (37 per cent) one month before transplanting of the crop. In case of TMV infestation, remove such plants immediately to avoid further spread of the virus.
Cleaning up between Tomato Crops:
Tomato crop is, usually, terminated in late June or early July depending on marketing situations. About 40-45 days prior to termination date, the plants can be topped by cutting the plants top at the trellis cable. Pollination can stop but fertilizer solution application is maintained. Fruits on the vine will continue to ripen and the last ones should be harvested by the projected termination date. Most of the growers prefer to have at least one month between crops for cleaning the house in preparation for the new crop.
Cleaning of the house involves removing the old plants and disinfecting the house and growing surface. For all cultural systems, plants need to be removed from the greenhouse and dumped/buried to avoid re-introduction of such insects and disease organisms.