Orchids are classified into three categories on the basis of their temperature requirement;

 1. The cool-growing Orchids 

These orchids grow best at night temperatures of 10-13 degrees centigrade and day temperature of 16-21degrees Centigrade. They come from the mantane regions of the tropics, e.g the large flowering Cymbidium, Odontoglossum, Miltonia etc. These plants have feeble growth in warm climates and never flower. Some attempts have been made to hybridize them with warm growing orchids (e.g.interspecific breeding in Cymbidium).

 2 The Intermediate Group

This group embraces the broadest collection of cultivated orchids and these plants prefer night temperature of 10-16 degrees Centigrade and day temperatures of 21-29degrees Centigrade. Cattleya, Oncidium, Dendrobium nobile, some Paphiopedilum,Epidendrum and a whole range of interesting botanicals belong to this group. Several orchids which usually grow in a warmer climate, e.g. Phalaenopsis, Ascocentrum and Vanda, will also thrive in the warmer parts of the intermediate orchid house.

 3. The warm-growing Orchids.

            These require night temperatures which are consistently above 16 degrees centigrade for proper growth and they are all natives of the tropical low-lands. During the day, especially in summer, it can be allowed to rise 30-32 degrees centigrade without the plants coming to harm. All members of the monopodial Vanda-Aerides tribe, including Phalaenopsis, belong to this group.

            This is the prime importance for the plants and consequently their capacity to produce flowers. In this context orchids may be divided into three major groups: those that live in full shade, in full sun and in an intermediate situation (semi-shade).

            Considering that the majority of orchids are epiphytic, it is the third condition which is most common. They receive only dappled sunlight through the forest canopy. Such orchids require 25-50% shade in summer if they are cultivated in temperate regions and throughout the year if they are grown in the tropics. The Dendrobium, Cattleya, Phalaenopsis and strap-leaf Vanda belong to this group. Some members of the Arachnis –Vanda (or Aerides) tribe are grown in full blast of the sun throughout the year. The only parts of the plant which may be shaded are the feeding roots which are hidden in the undergrowth. These orchids and their hybrids like full sun throughout the year and will only flower if they receive strong sunlight.

The terrestrial orchids have a much lower light tolerance for thy grow either in the deep shade of the forest, in bogs or in open bush-land where they are protected from the full sun by other plants growing in the bush. Under cultivation, these require 60-75% shade. Examples are Paphiopedillum, Cyperipedium. Shade in the greenhouses may be provided with nets of varying sizes of mesh and preferably of a dark color, with matting, or with white paint on the outside of the panes-all easily removable when no longer necessary.

            The type of lights is also important for proper growth of the orchid. Light in the ultra-violet, and green ranges represses plant growth and green PVC (poly venyl chloride) sheets are totally unsuited for roofing of orchid houses. When too much green algae collect on top of the plastic roofing it similarly represses plant growth. The algae must be scrubbed off or the roofing replaced.

            For vegetative growth, orchid can be grown in continuous light day and night to achieve maximum growth. However, day length, or more correctly night length, affects flowering. Increased light, higher humidity and lower day temperature would always lead to better growth and flowering.

            A high level of surrounding humidity is essential for plants that originally come from tropical zones; in no instance should this below 50%. A rise in temperature means a drop in humidity, so during the warm months of the year various methods have to be used to control level. Humidity can be increased by damping down the greenhouse paths and the areas beneath the shelves, or by using humidity trays indoors. Here the floor should be of clay, sand or gravel, which gives off moisture.

            The most widely collected orchids are for the most part epiphytes and can be cultivated in supports with the roots left to grow in the air. Epiphytic orchids cannot be potted in soil because their roots require good aeration. If they are waterlogged they soon begin to rot. As the plants grow and are repotted into successively larger pots, bigger pieces of crocks, charcoal, fir bark or tree fern have to be added to ensure that water is drained off effectively after it has wet the roots. After two or three years, the root ball becomes too extensive and the potting medium would have deteriorated and collapsed, causing a constriction of the air spaces which then become waterlogged. To avoid this, most growers repot at least once in two years. An alternative approach is to remove the forward bulbs from the back-shoots to produce keikis which can be removed and repotted wherever they produce sufficient roots.

            Air that is constantly moving is a good guarantee of health in orchids. Commercial growers pay lot of attention to wind movement when selecting a site for an orchid nursery. Strong wind movement is favorable and good site should have sloping terrain and should be obstructed by tall structures. Orchid leaves are heated by radiant energy and can only lose this heat by conduction into the atmosphere. It is therefore important to have good air movement and high humidity around the plant since water conducts heat more efficiently than dry air. If the plants are watered in the evening, a strong currents will also lower night temperature and induce flowering.

            A greenhouse for orchids, whether hot, temperate or cool, should be a pleasant environment. A well-ventilated greenhouse receives good circulation of fresh air. Ventilation lowers the temperature, and dries out and eliminates any standing water that is especially likely to harm the plants when the temperature goes down. In well ventilate surroundings plants are not seriously harmed by temperature several degrees lower than the minimum recommended. An adequate circulation of air, together with suitable heating of greenhouse will prevent many fungal and bacterial attacks.

            The answer to the question “How should I water my orchids?” is no easy because it depends on many factors. Are the plants in a pot or on a raft? What soil is being is used? Adult or young plants? Where have been grown? First of all, one has to know the cultural requirement of the plants, particularly in relation to their rest period. In the cool, temperate regions, plant growth slows down in autumn and may come to a halt in winter. Watering should be reduced during this period.

            As a rule, plants grown in a raft, whatever the constituent material, should be sprayed very frequently, even several times a day in the growing season, and watered plentifully at least every other day. For plants kept in pots, it has to be remembered that growing longer than bark, charcoal and perlite. These materials may be used either pure or mixed in different proportion, according to the needs of the various plants.

           Plastic pots, lighter, unbreakable and easy to disinfect, retain moisture better and longer than clay pots or baskets. Young plants, with a less-developed root system and more delicate growth, need watering more often than adults of the same species.

           Given all these consideration, it is fair to say that adult plants, grown in plastic pots, with bark, should be watered in average once every 5-6 days, and although this may vary by a few days either way depending in the alternative factors mentioned above.

            It is best to water orchids in the morning, preferably in a fine day, so that any standing water, harmful to the health of the plants, can disappear by evening.

         There is no doubt that orchids benefit from the application of fertilizer. A fertilizer equally balanced in nitrogen, phosphorus and potassium (18-18-18), dissolved in the ratio of 1 gram to 1 liter and applied once a week for approximately ten months (from late spring to early winter), and a food containing more nitrogen (30-10-10) during the remaining part of the year will provide a sufficient supply of nutrients to give luxuriant, free-flowering plants. Nitrogen is necessary for the formation of proteins and a good supply of nitrogen is the key to rapid vegetative growth. However, continued application of high nitrogen fertilizers produces soft growth and may delay flowering.

        It is advisable to water the plants abundantly prior to feeding in order to wash any residues of mineral salts and to wet the roots in preparation for a new feeding. An accumulation of salts can

cause serious scorching of the roots, especially if the compost is not sufficiently moist.

            Orchids as a rule are repotted every three years. The best time to do this is when the plants resume their growth and the new roots begin to sprout.

           Since orchid roots are fleshy and sometimes fragile, they need to be fairly dry when handled so that they quickly, start to grow again and branch out. Compost for repotting should therefore be moist but not waterlogged. If bark is used, choose pieces in the dimensions as per the plants size.

           After a plant has been removed from the old compost, rotten roots, pseudo-bulbs and dead stems should be eliminated; the plant then be replaced in a new pot of suitable dimension, and positioned either center or off-center according to its structure, so that as much space as possible is left for its growth. The compost should be placed between the roots and firmly pressed down so as to give the plant stability. If necessary the plant can be tied to a stake. Unlike most plants, orchids need not be watered after repotting for atleast two weeks, until the roots start growing again. Frequent spraying and a high level of surrounding humidity will help the plants weather this critical period.

          Carbon copies of the orchid can be produced through the vegetative propagation which can be achieved by four methods:

1.                  Division of the plants, otherwise know as cutting.

2.                  Shoot development on old back bulbs.

3.                  Stimulation of plantlet formation on flower stems.

4.                  Meristem tissue culture.

            This method is suitable for both monopodial and sympodial orchids. In case of sympodial orchids, the following conditions should be made before dividing the plants:

1.                        It should be healthy. If the plant is weak, it is better to remove a back bulb.

2.                        It should have four matured stems, preferably more.

3.                        A new pseudobulb should be developing from the base of the old one and just beginning to send out its own roots.

          A clean cut is made in the rhizome, leaving at least two mature pseudobulbs attached to the young one to provide it with nourishment. After sealing off the cut ends with fungicide or tar, divided plant can be left in the pot or the younger segment can be removed and repotted. The back portion will produce at least one new pseudobuld if it is healthy.

If the original plant is large and extensively branched, several cuts can be made, each segment to be left two or three strong pseudobulbs will develop, one or two behind each cut on t horizon. If the plant is left in the pot, it will produce a spectacular flowering when all the new pseudobulbs send of their blooms.

When doing this, it is customary to trim off all the old roots, but many growers will leave the old roots behind if they are healthy and still capable of absorbing water and nutrients. Clear off all the old potting medium and soak the roots in fungicide before repotting.

        In case of monopodial orchids the optimum time for cutting is:

1.             When the top cut portion will have at least three strong roots, and

2.             The bottom segment is left with at least six leaves and four unflowered leaf axils.

                        Make a clean cut with pruning shears, not with a knife. Seal off the cut ends with coal tar or a fungicide and allow the tip to dry before replanting the top portion. After a few weeks the bottom segment will produce several new shoots and when these have developed two or three strong aerial roots, they may be removed and replanted.

           If the aim is to propagate the plant, it should be given 50 per cent or even heavier shade, liberal watering and heavy nitrogen feeding. This will stimulate rapid soft vegetative growth and prevent flowering. Take care to spray fungicide at close intervals because under such growing conditions the plant is prone to bacterial and fungal rot. When making a top-cutting, more of the stem is left behind in order to obtain additional offshoots. If the offshoot is very strong, and there are no more axillary buds left on the main stem, it need not be removed completely; instead a short stump of the offshoot bearing two or four leaves can be left behind on the old stump, and this in turn will yield another generation of offshoots.

          A higher yield can be obtained by making multiple cuts on the stem but this can only be done if the plant has been grown so that its roots are firmly attached to a broad stump of wood. Each division should have six leaves and they are al left attached to the original support. Shading is increased, and liberal watering and heavy nitrogen fertilizer is given. After a few weeks, three or four offshoots will develop from each segment. When these are strong enough, they may be removed and repotted.

Instead of removing the new lead as described above, one or two old pseudoublbs at the end of the rhizome may be removed. This may actually strengthen the plant left in the pot. The pseudobulb is hung up under shade and watered occasionally until a new shoot develops, when it can be replanted in the usual way. If the lowest bud is healthy it will be the one to develop into a now shoot; otherwise any bud along the length of the pseudobuld may develop into a new plant. Various methods are employed to increase the humidity around the back bulbs to encourage the development of offshoots. Some of these are layering on peat and sand, or dropping back bulbs into a polythene bag which contains a small amount of moist sphagnum moss.

        Production of plantlets on the flower stem is commonly exhibited by Phalaenopsis and its intergeneric hybrid, and the old inflorescences of Oncidium, although, vary rarely, the flower stems of Dendrobrum may become vegetative and turn into a plantlet. Old of such species should always be left on the plant after flowering for they are frequently the source of bonus plants. Plantlets so develops are known as Kiekie. Some orchidists developed a paste which caused Keikis to develop on the flower spike. An aqueous cream with 0.05 to 0.5% benzyl adenine when applied to flower spikes caused the axillary buds to soil and in most instances to develop into single plants or clumps of plants. To obtain a 0.05% concentration, mix 0.5mg of banzyladenine with 1g of cream or lanolin. Select only old flower spikes which have finished flowering a few weeks earlier. After removing the bracts from the two internodes beneath the first flower, apply the paste lightly to the bud. These axillary buds will swell after four days and the first leaves will break through after a fortnight. After two or three months some plantlet will develops roots; a few may take longer. Leaves of these plantlets are vary succulent until the have developed strong roots. It is a temptation to apply deepest on all the nodes on the flower spike but this will probably weaken the parent plant and the benzyl adenine may inhibit the growing point on the plant. It is safer to produce only one or two plantlets on a single inflorescence. On the other hand, if the parent plant is dying from crown rot or weevil attack, then one may feel free to treat all the axillary buds.