Everything you need to learn about the cultivation, production and growth of cucumber in greenhouse!
Cucumber in the recent years, has become important and gaining popularity in greenhouse cultivation in Europe, USA and Israel. Three crops of cucumber can be grown in naturally ventilated greenhouse in a year under north Indian conditions for all the year round supply of high quality cucumbers to the up-market in metropolitan cities.
Botanically, the fruit is a false berry or pepo, elongated and round-triangular in shape. Its size, shape and colour vary according to the cultivar. In the immature fruit, chlorophyll in the cells under the epidermis causes rind to be green, but upon maturity it turns yellowish white. The epidermal layer may have proliferated (warty) areas, each bearing a trichome (spiky hair). The fruit cavity (three locules) contains soft tissues (placenta) in which the seeds are embedded.
The regular cucumber bears actual seeds (seeded cucumber) whereas the English cucumbers bear either no seeds (seedless cucumber), or rarely distinguishable atrophic seeds. Regular cucumbers are short (about 15 to 25 cm) and uniformly cylindrical. Their thick, deep green skin has light green stripes and a rough surface with strong trichomes. The skin is bitter in taste and not easily digested so the fruits need to be peeled before eating.
The English cucumbers are long (about 25-50 cm) and cylindrical with a short and narrow neck at the stem end. The smooth surface has slight wrinkles and ridges. The thin skin is uniformly green and bitter less, thus is consumable without peeling.
Climate and Soil Requirement for Growing Cucumbers:
The cucumber is a semi-tropical vegetable and grows best under conditions of high light, humidity, moisture, temperature and fertilizers. Under favourable and stable environmental and nutritional conditions when pests are under control, the plants grow rapidly and produce heavily.
The cucumber, however, is more sensitive to temperature, which may cause reductions in both growth and yield. It is relatively a short season crop and cannot tolerate frost. The optimum temperature for better development of fruits is 14 to 20°C. Cucumber requires mild climate and as such does well under greenhouse conditions.
It does well on well drained sandy loam soils. Heavier, wet and poorly drained soils should be avoided. Cucumber can tolerate strongly acidic soils but best results are obtained with soil pH of 5.5 to 6.8.
Temperature:
Air temperature is the main environmental component influencing germination, vegetative growth, flower initiation, fruit growth and fruit quality. Greenhouse cucumbers are more sensitive to low temperature than tomatoes. The minimum temperature should not be lower than 18°C for sustained production.
Prolonged temperature above 35°C should also be avoided as fruit production and quality are affected at extremely high temperature. Cucumber seed germinates rapidly (2-3 days) at an optimum germinating temperature of 26-28°C in the germinating room. Once the seed has germinated, remove the seed tray covers and reduce the temperature to 22°C, and supply as much light as possible continuously.
Maintain these conditions for the next 5-7 days until seedlings attain enough growth that they can be safely handled, but not for too long as the seedlings may get crowded, etiolated and grow too slender. The growth rate of the crops depends on the average 24 hour temperature. The higher the average air temperature the faster the growth.
The larger the variation in day-night air temperature, the taller the plant and smaller the leaf size. Although maximum growth occur at a day and night temperature of about 28°C. Maximum fruit production is achieved with a night temperature of 19-20°C and a day temperature of 22-24°C.
Light:
Light plays an important role in plant growth as it facilitates photosynthetic activity by the plant. It is absorbed by the chlorophyll in the green parts of the plants i.e. leaves, which are food synthesis factories of the plant. The rate of photosynthesis relates to light intensity, although it is not proportionate. During winter, light assumes more importance because it is scarce.
Relative Humidity:
High relative humidity generally favours growth. However, reasonable growth can be achieved at medium or even low relative humidity. The crop can adjust to and with stand relative humidity from low to very high but reacts very sensitively to drastic and frequent variation in relative humidity. Its sensitivity to such variation is greatest when the crop is developed under conditions of high relative humidity and also increases the risk of water condensing on the plants and the development of serious diseases.
High relative humidity results in low transpiration rate, which leads to inadequate absorption and transport of certain nutrients, especially calcium to the leaf margin and fruit. At low relative humidity, irrigation becomes critical. Furthermore, low relative humidity favours the growth of powdery mildew and spider mites, which alone can justify installing and operating misting devices.
Cucumber Plant Growth Habit:
The cucumber is a coarse, prostrate, annual vining plant with stiff hairs or spines on leaves and stems. Unbranched lateral tendrils emerge from the leaf axil and vining begins after two or three leaves are formed and branching is also initiated simultaneously. As soon as branching begins, flower clusters also start emerging in the leaf axils.
Cucumber plants are indeterminate in growth habit, producing fruits continuously on new growth like that of greenhouse tomatoes. The main stem laterals and tendrils grow fast. They need frequent pruning to a single stem and training along vertical wires to maintain an optimal canopy that intercept maximum light and allow sufficient air movement.
Under optimal conditions, more fruits may initially develop from the axil of each leaf that can later be supported to full size by thinning. The over fruited plants become exhausted, abort fruit and fluctuate widely in productivity with the passage of time. Rapid growth, thick and brittle stems, large leaves, long tendrils, deep green foliage, profusion of fruit, and large, deep yellow flowers indicate excessive plant vigour.
On the other hand, cucumbers are very sensitive to unfavourable conditions, and the slight stress affects the growth and productivity. Because fruits develop only in newly produced leaf axils, therefore major pruning may be needed to stimulate growth, the removal of entire weakened laterals is more effective than snipping back the tips.
Selection of Cultivar for Producing Cucumbers:
Selection of cultivar is one of the most important decisions made during the crop production process. There are several cultivars available for greenhouse cucumber production. Several factors should be considered when selecting a cultivar, including disease resistance, plant vigour, early and total yield, fruit size and colour, and general fruit quality.
The main criteria in selecting the best cultivar are as follows:
(i) Overall productivity
(ii) Plant growth habit and vigour
(iii) Fruit quality i.e. length, diameter, shape, colour and smoothness
(iv) Fruit shelf life
(v) Disease resistance, and
(vi) Energy requirement
The cucumber varieties grown in greenhouses are usually as European types. These special cucumber varieties are gynoecious and set fruits parthenocarpically fruit development takes place without pollination. Such varieties cannot be grown in open field as natural pollination may result into bitter fruits which in turn becomes club shaped at the blossom end and seed.
It is, therefore, essential to prevent bees and other pollinators from entering the greenhouse as they carry pollen from outdoor gardens or field cucumber plantings. These varieties generally produce higher yield and the fruits are 12-20 inches long, having slightly wrinkled surface, uniformly green, thin skinned and usually have a short neck at the stem end. Such fruits are consumed without peeling.
There are three types of cucumber varieties. They are sub-divided on the basis of flowering habit:
(i) Gynoecious, which produces only female flowers
(ii) Pre-dominantly gynoecious, which also bears some male flowers, and
(iii) The monoecious, which produces both male and female flowers.
The first two types produce fruits parthenocarpically, whereas monoecious types require pollination and does set seeds. Predominantly female types can be used with confidence, because they are less vigorous requiring limited pruning, come into production earlier, produce more and can grow at a lower temperature.
Cucumber cultivars are generally classified into four main groups:
(i) Field cucumbers with prominent black or white spines
(ii) Greenhouse or forcing cultivars, also referred as English cucumbers
(iii) Sikkim cultivars with reddish-orange fruits, and
(iv) Small fruited cultivars often used for pickling.
Some important gynoecious varieties from Europe and Israel are Hasan and Sarig (for summer crop), Muhasan and Dinar (for winter season), Mustang and Bronco (for spring crop), Kian, Alamir and Nun-9729.
Monoecious varieties available in India can be grown inside the greenhouses, but pollination is required for fruit setting. Honey bees are, therefore, necessary. The important parthenocarpic varieties available in India are Satis, Alamir, Nun-9729, Nun-3019 and Kian. Some important monoecious varieties are also available in India which can be grown in greenhouse only through pollination management. These monoecious varieties are Japanese Long Green, Pusa Sanyog, Priya and Poinsett.
Nursery Raising and Planting for Growing Cucumbers:
For greenhouse cultivation first the nursery is raised on soil-less media in plastic pro-trays, having cells of 1.0 to 1.5 inch size. Coco-Peat, vermiculite and perlite is used in 3: 1: 1 ratio as a media for raising seedlings. About 600 g seed is sufficient to raise the nursery for one hectare area. One seed is sown in each cell. During the seeding and transplant production stage, the plants must never become stressed for water or nutrients.
The seedlings are ready for transplanting within 28-30 days in winter season and 15-18 days in summer season but proper root development is required for transplanting of the crop. The transplants should maintain an upright growth habit to aid in successful transplanting. Usually, greenhouse cucumber is grown under drip irrigation system.
Spacing in Cucumber Plants:
Greenhouse cucumber plants have very large leaves, grow vigorously and require plenty of sunlight. The optimum space per plant generally agreed to is 70 to 80 cm2. Ideally, use the same spacing between rows of plants as between plants in the row. One row is planted on one bed and the spacing between rows is kept 1.4 to 1.5 m and 30 cm between plants.
Sometimes, during summers two rows are planted on a bed with 60 cm spacing between rows and 30 cm amongst plants. But for better light availability to the crop only single row is planted on each bed. Factors such as cultivar, season and growth medium influence the plant spacing.
Space the plants in the rows 45-60 cm. Exact row and within row plant spacing depends on the training system chosen. Although, it is important to choose the space in the greenhouse as efficiently as possible but, excessive crowding usually results in small fruits and outbreak of leaf diseases.
Training and Pruning Cucumbers:
Several training systems exist for greenhouse cucumber. The basic principle in developing a training system is to uniformly maximize the leaf interception of sun light throughout the house. The selection of a system will largely depend on the greenhouse facility, the production system and the preference of grower.
The plants are trained upward so that the main stem is allowed to climb to the overhead wire along a polythene twine. Wires are fixed 8-9 feet above the ground. The twine of each plant is alternatively tied to the horizontal overhead wires or steel cables running along with the length of the rows.
The base of the twine (string) is anchored loosely to the base of the stem with a non-slip noose. As the stem develops, it is trellised on the twine up to the height of horizontal wires (8-9 feet height) and then the plants are again trained to downward direction. Trellising of the plants is done carefully to avoid any damage to the flower buds appeared on the main stem.
No fruit is allowed on the main stem up to 1.5 to 2.0 feet above the ground. All the laterals are removed that appear for the first two feet of main stem. Pruning of each plant is based on the plant vigour and fruit load. Extensive leaf growth should be discouraged to allow proper colouring of the fruits.
The development of the fruit is dependent on the continuing production of leaf axils. Fruit thinning is necessary to avoid malformed and non-marketable small fruits in case excessive fruit setting occurs. Multiple fruit occurrence in axils should be thinned to one. Weak and unproductive laterals should also be removed.
Pruning involves making a series of decisions based upon the basic concept of plant growth. Although, pruning usually causes remaining shoots to increase in length and leaf area, especially near the cuts, but total plant size and weight is maximum without pruning.
Thus, pruning is a dwarfing process:
The main reasons for pruning the plants are as follows:
(i) To help recovery from injury to roots.
(ii) To remove dead or injured growth.
(iii) To remove or restrict unwanted growth.
(iv) To encourage or train growth where it is desired.
(v) To rejuvenate old plants.
(vi) To promote flower and fruit production.
(vii) To facilitate light penetration throughout the leaf canopy for more efficient use of light.
(viii) To expose fruits to light when beneficial.
Pruning and training of greenhouse cucumber plants create conditions for maximum yield of high quality fruits by establishing and maintaining:
(i) Optimum fruit load.
(ii) Complete leaf coverage i.e. no light reaching the ground.
(iii) Uniform exposure of entire foliage (for efficient light absorption).
Although training for practical reasons is uniform for all plants, pruning offers opportunity to adjust the fruit load of each individual plant according to its vegetative vigour. Maintaining the proper balance in each plant is essential for maximum productivity and best fruit quality throughout the crop period.
Fruit Thinning:
Over bearing can sometimes be a problem. So the plants protected from becoming exhausted through selective fruit thinning besides improving the fruits size and limiting the number of fruits per plant. This technique is powerful, so use it with great caution. The optimum number of fruits per plant varies with the cultivar and even more with the growing conditions.
The limiting of fruits per plant invariably results in premium priced large fruits. Retaining of optimum fruits per plant is the most deciding factor of quality and quantity of fruit yields. Fruit thinning is undoubtedly most useful in the hands of the experienced growers, who can use it to maximize their financial gain.
Fertigation in Cucumbers:
Cucumber requires a constant water supply to reach high quality yield. During the period of growth, flowering and fruit enlargement, the plant is most susceptible to irrigation deficit. The frequency of irrigation is largely dependent on soil type and weather conditions. In general, greenhouse cucumbers are irrigated through drip system of irrigation, and fertilizers are also applied along with irrigation water according to the crop growth and season of cultivation.
Greenhouse seedless cucumbers have a high nutrient requirement and grow very rapidly when supplied with sufficient nutrients. The maximum demand for nutrients is during the peak fruit production period. Nitrogen and potassium requirement is more, however, a complete nutrition programme comprising essential minor elements needed.
It is, generally, sensitive to N deficiency and grows slowly and produces less flowers and smaller fruits in low N regimes. In addition to N, P and K, calcium is also required for enhancing fruit quality and yield, especially during intensive cultivation of cucumber. The fertilizers are applied in liquid form along with irrigation known as ‘fertigation’.
During summer season fertigation is done twice a week, whereas during mild winters the interval is 7 to 8 days. However, during peak winter the interval of fertigation is 10 to 12 days, although soil type and growth of the crop are also deciding factors.
Sometimes, magnesium deficiency may cause loss in yield and quality while intensive cultivation of cucumber is being done which can, however, be corrected by applying either magnesium sulphate into the soil prior to planting or fertigation with magnesium sulfate @ 35 kg per hectare should be done.
Pollination in Cucumbers:
For growing gynoecious varieties of slicing cucumber, there is no need of pollination – in greenhouse conditions. Pollination is also not required in case of pre-dominantly gynoecious varieties. Monoecious varieties, however, are dependent upon pollination inside protected structures, which is mainly performed by honeybees. Eight to ten visits per flower are required for adequate fruit formation in cucumbers.
One beehive (20000 bees per hive) is sufficient for 1000 m2 area of greenhouse cultivation of monoecious cultivars to obtain high yield with high quality fruits. The direction of the beehive in the greenhouse is very important along with proper ventilation. Precautions should also be taken that pesticides are not sprayed during bee activity period.
Harvesting and Storage of Cultivated Cucumbers:
Time from transplanting to first harvest is generally 35-40 days in gynoecious cultivars of slicing types and 45-50 days in monoecious varieties of cucumber, but it entirely depends upon the climatic conditions and crop management practices. Fruits are harvested when they are more or less cylindrical and well filled.
Fruits keep on developing as the plants grow and reach harvestable stage in 10-14 days after flower opening. Therefore, fruit picking is a continual process usually done three times a week. Harvested fruits must be protected from desiccation and bruising because the skin is rather tender and prone to water loss.
With good crop management of gynoecious cultivars, one can harvest 40-45 quintals of cucumbers from 1000 m2 area with one crop of 3 to 3.5 month duration and normally three crops of cucumber can be taken from the same area in one year with a quality fruit yield of 150-180 tonnes per hectare.
Pick the fruits carefully and place them in soft plastic or padded containers to avoid bruising and damage. The size of the fruits at harvest is important. Harvesting of underdeveloped fruits losses revenue because larger fruit sells easier at better prices. However, fruits left on the plant too long not only prevent new cucumber from developing but also has a short life expectancy when harvested.
Overfilling of the crate or staking the produce too high may damage the bottom layer. Harvest the fruits in the early morning while the day is still cool. Move the produce immediately from the direct sun light and to cool, shaded and ventilated areas so that the fruit temperature does not rise.
Cucumber fruits are picked manually. The fruits should be held near the stem and clipped or snapped with a slight twist motion and should not be pulled off the vines to minimize “pulled ends”. Pulled off fruits leave an open ‘wound’ where the fruit skin is torn off and this cause the fruit to shrivel around the support.
Fruits are also harvested with the help of scissors or knives to avoid any injury to the fruits. After harvesting, the fruits are graded according to size, shape and colour of the fruits and after proper packaging marketed to various high markets on higher price. After all the effort and money invested in production it is essential that fruits be handled well at harvesting, grading and during transportation to the market.
European greenhouse cucumbers have a very thin skin resulting in high susceptibility to water loss and softening of harvested fruits. Immediately after harvest, the containers should be avoided from the exposure to direct sun light. Each fruit is individually wrapped in a shrink-wrap film before packaging. Shrink-wrapping will minimize moisture loss and extend shelf-life by several days.
Greenhouse cucumbers are also highly susceptible to chilling injury caused by exposure to low but non-freezing temperature. Chilling injury can occur at a temperature below 10°C for most of the vegetables. Chilling injury in cucumber fruits results in a pitting of the fruit surface and a tendency for more rapid loss of green colour. Fungal decay often follows chilling injury.
During transportation, minimize heat gain and place produce in cold storage (12°C) as soon as it arrives at its destination. Fruit stored under ideal conditions i.e. 10-13°C temperature and 90-95 per cent of relative humidity has a life expectancy of 10-14 days. Staking of the crates too high or too tight prevents the crates in the middle from cooling down adequately when the product is stored in a cooler place.
Cucumbers are also sensitive to ethylene gas, therefore, it is necessary to avoid the storing of cucumbers along with active ethylene producers such as apple and tomato, which accelerates ripening and results in yellowing of the fruits. Exposure to levels of 1 ppm ethylene for one day at 15°C will result in a noticeable yellowing of the fruit. Chilling injury to cucumber fruit, even for a short duration will increase the production of ethylene by the fruit. After harvest, the quality of cucumbers can only be preserved, not increased.
Cucumber Plant Protection:
Greenhouses or protected structures are designed in such a way to minimize or eliminate most of the insects and some of the diseases. This is possible with the use of anti-virus nylon nets of 40 to 50 mesh size (usually ultra-violet stabilized) on all sides of the greenhouse or other low cost protected structures.
Preventing the insects from entering in the greenhouse is the best way of controlling insect problem in the greenhouse for cucumber cultivation. The use of disease resistant varieties also helped to reduce disease problems. The common diseases, which occur in the greenhouse cucumbers are gummy stem blight, powdery mildew, downy mildew and damping off.
For the control of gummy stem blight, soil sterilization is quite effective. Good sanitation, crop rotation and good ventilation is required. Weekly spray of fungicides can control the disease. Downy mildew disease can be controlled easily by spraying the crop with mencozeb @ 2.0 g in one litre of water as soon as the symptoms of the disease appear on the vines.
Soil sterilization with methyl bromide or formaldehyde is effective against the fungus causing damping off. Monoculture of cucumber for years can increase the intensity of Fusarium, crop rotation, therefore, is necessary for cucumber cultivation under greenhouse conditions.
Where root rot diseases such Fusarium and corky root are present in the soil, cucumber seedlings of the desired cultivar may be grafted on to the resistant root stock such as pumpkin. Viruses like CMV and ZYMV also cause serious problem for the greenhouse crop. For the control of viruses, use of resistant variety is the best way. The affected plants, if at all, should be removed as soon as possible from the greenhouse to avoid further spread of the virus.
Among the insects, outbreaks of carmine spider mites occur very frequently, especially during hot weather conditions. Mites feed on the plant sap and prefer to live on the under-side of leaves. Their feeding causes stippling of white area on the leaves. Severely infested leaves may turn yellow and drop off prematurely.
Most of the miticides do not kill at the egg stage, so several applications are required for effective control of the insect. Dicofol or ethion can be sprayed @ 2.0 ml per litre of water, but the spray must be directed to the lower side of the leaves for effective control of the mite.
Sprays are repeated as per requirement of the crop. Varietal differences exist with respect to tolerance to mites, but no resistant variety is currently available. Sometimes aphid also affects the greenhouse cucumber crop and can be controlled by spraying confidor @ 1.0 ml per litre of water.