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Horticulture

Orchids

Introduction:

Orchids are considered as the most beautiful flowering plants for the exquisite beauty of the flowers, variety of fragrance, brilliance in colour, unusual shapes, variation in form and attractive growth habits. There are about 24,000 species and 32,000 hybrids of orchid.

Development of new hybrids and commercial production of cut flowers in orchids are expanding rapidly in the U.S.A. Europe, Thailand, Malaysia and Singapore. There is immense scope for improving orchids in India, because large number of species are native to this country and many of them have already proved to be important parent plants and contributed in the production of several outstanding hybrids in the world. Due to the diversity of environmental condition in India, it is possible to grow all types of orchids in suitable places without the control of environment.

Forest is the natural habitat of orchids. More or less similar environment can be created by growing the plants in greenhouse and protecting them from direct scorching sun, dry wind and by maintaining high humidity.

Warm Climate Orchids:

Orchids which suit warm climate condition and can be successfully grown in ordinary greenhouse include the numerous hybrids of Cattleya, Dendrobium, Onicidium, Phalaenopsis, Rhynchostylis and Vanda, Orchid species producing beautiful flowers e.g. Aerides longicornu, A. multiflorum, Arachnis crispum, A. maculosum, A. odoratum, Anoectochilus roxburghii, Arachnanthe catchcartii, Arundinia bambusaefolia, Calanthe densiflora, C.masuca, Coelogyne flaccida, C.ochracea, Dendrobium aggregatum, D.densiflorium, D.devonianum, Phaius macutatus, P.wllichii, Phalaenonsis manii, P. parishii, Pleione maculata, Renanthers imschootiana, Rhynchostylis retusa ,Saccolobium ampullaceum S. dasypagon, S.trichromum, Thunia alba,Vanda coerulea,V.coerulescens, V.cristata, V.teres and many others grow and flower well in the above enviornment.

Orchid House And Its Management: -

A free standing flat-roof orchid house shaded by spit bamboo or wooden batten is recommended for housing of orchids suitable for warm climate. The temperature range suitable for most of those orchids is 65 to 850F. For satisfactory growth of orchids, atmospheric humidity should not be less than 30 per cent at night and 70 to 80 per cent during the daytime. Monopodial orchids like Vanda, Phalaenopsis require high humidity, whereas sympodial type e.g. Cattleya, Laelia or those with leathery leaves need less humidity. The atmospheric humidity will increase if small tanks or lily pools are located inside the orchid house and the floor space is covered with sand, soil, cinder, etc. instead of concrete. Free circulation of air is needed for the orchids to grow and flower and light intensity ranging between 1500 to 2000 feet candle in midday is good enough for most of the orchids.

Seed Sowing and Care of Seedlings: -

Seedpod of orchid grow after fertilization, and ripens in six months to one year. After ripening the seeds are collected and stored in a cool and dry place or in a desiccator. Millions of powdery seeds are released from each pod and they contain little or no food to nourish the embryo. Under natural condition, the seeds germinate when they find a right pocket of decaying vegetable matter on the trees.

Seeds of orchids are germinated and seedlings grown in culture media containing agar, inorganic nutrients and sugar. Disinfected seeds are sown in sterilized flasks containing agar-nutrient media and the seedlings grow for 8 to 12 months before they are transferred.

The seedlings are removed from the flask and planted in the community pots, 7 to10 cm in diameter which hold about 20 to 25 small plants. The compost used for seedlings in the community pot is a mixture of equal parts of the finely chopped tree fern and dust-free crushed bark or moss. A shady but well aerated location in the greenhouse will promote the growth of seedlings. In the community pot, the seedlings are watered daily and during the summer months they may be sprayed with water two to three times a day.

With the increase in size and vigour, each plant is transferred in a small pot, using the same compost recommended for larger plants, but at this stage they benefit by feeding with the weaker concentration of fertilizer solution.

Vegetative Propagation: -

Besides multiplication by seeds, commercial method of vegetative propagation of hybrids of Cymbidium, Phalaenopsis and Cattleya is done by meristern culture and large number of plantlets develop from a small piece of growing apex. Amateurs, however, propagate their plants by offsets, air layering, cuttings and division. Offsets develop from Dendrobium and some Epdiendrum, which can be detached and planted in small pots.

Air layering is practised on the monopodial types like Vanda. A slant cut is given halfway in the stem and wrapped with sphagnum moss. When roots are noticed in the moss, the upper portion of the plant with roots is detached and potted.

In Arachnis, Renanthera and to a lesser degree in Vanda propagation is done by cutting. As these large-sized plants produce adventitious roots, the stem is cut in section 3 to 4 nodes, placed in a cool and dry place for healing of wound and allowed to root in moist sand or damp sphagnum moss. Plants of many genera such as Cattleya, dendrobium, etc., produce new growth from a lead and they can be propagated by division at the time of repotting.

Potting and Compost:

A vigorous and healthy root system often indicates good vegetative growth of the plants, which largely depends on the pot compost. Ideal rooting media will provide high degree of porosity and ensure adequate oxygen for root respiration. Water should drain out freely through the media and it should be resistant to rapid decomposition and decay.

Depending on the growth habit, i.e. terrestrial or epiphytic, orchids are potted in a wide variety of media and compost. Epiphytes like Cattleya, Epidendrum, Phalaenopsis Vanda, Dendrobium, Rhynchostylis, etc., are planted on a very light rooting media, consisting of various kinds of tree fern fibre or on larger pieces of hard charcoal. Terrestrial orchids like Phaius, Calanthe, Thunia, etc., thrive best in the mixture of leafmould, loamy soil, sliversand, dried cowdung manure, charcoal and chopped tree fern fibre. Epiphytic orchids are best grown in speciality designed orchid pots with holes at the bottom and slits or perforations on the sides. Monopodial epiphytes like Aerides, Phalaenopsis, Vanda, etc., are particularly suited to basket culture because of the large aerial roots produced from these plants and straight growing habit. Many orchids are conveniently grown on the branches of the trees, charred wooden slabs or tree fern blocks.

Orchids grow better if undisturbed, Phalenopsis, Vanda, Laelia and some species of Dendrobium should not be repotted unless it is absolutely necessary. Cattleya and many Dendrobium species and hybrid need repotting when roots become pot-bound.

Watering and Spraying:

As orchids are grown in a light and porous compost, watering is very important. Atmospheric humidity influences evaporation of moisture from the compost and orchids, in general, prefer high relative humidity. In a dry and will-ventilated atmosphere, damping down of the floor of the greenhouse, frequent overhead sprinkling of water will increase the humidity. But in high humid atmosphere watering should be less frequent. Alkaline water is injurious to orchids and slight acidic water or at pH up to 7 should be used.

Newly potted plants should not be watered very frequently but the compost is kept moist by fine spraying. As new root emerges and growth starts, the plants need more frequent watering and it should be decreased again after flowering. Fine spraying of water is also very beneficial to plants during the period of growth or on warm dry days.

Nutrients:

It has been observed that growth and flowering or orchids are improved markedly by the application of fertilizers in liquid form and a number prepared fertilizers are available in the orchid-growing countries. A balanced feed on nitrogen, phosphate and potash in the ratio of 10:12:10 and very small amount of magnesium, calcium, manganese, iron, boron and zinc has been found very effective on a large number of species and hybrids. For mature and flowering plants. Two table spoonful of the above fertilizers mixed in 10 litres of water is sprayed once a week, while a more dilute solution is used on seedlings. Leaves and rooting media should be thoroughly sprayed with the fertilizer solution.

Diseases and Pests:

Orchids are less subjected to the attack of pests and disease. Scale insects, mealy bugs, green fly, thrips, red spider and snails may cause considerable damage, fly, thrips, red spider and snails may cause considerable damage, if they are not controlled in time. Application of Rogor or Malathion is very effective to keep the orchids free from pests.

Die-back is a serious disease in orchids which starts in rhizome and if left unattended, it spreads to other plants in the orchid house. Orthocide 50 and Cossan are recommended for controlling fungus diseases on orchids. Virus infection is also common in several species and varieties of orchids. Sometimes black spots appear on leaves and flowers turn yellow and drop off. This is not caused by fungus but due to faulty culture like over-watering insufficient ventilation, too much of light or very dry atmosphere.

Cleanliness of the greenhouse and regular attention to the plants are very important to keep the plants free from diseases and pests.

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