Pamphlet No. 12 of the SOUTH AFRICAN BIOLOGICAL ASSOCIATION, pp. 25 - 33


JANUARY 19TH, 1943).

The growing of orchids on a commercial scale has up to now never been undertaken in this country, notwithstanding the fact that the demand for cut flowers of orchids is steadily increasing and can be met only occasionally when the small number of private enthusiasts are willing to part with their flowers.
The reasons for this state of affairs are;—
(1 ) lack of sufficient knowledge with regards to culture ; and
(2) fear of the demand being too limited to warrant the costs of production.
It is hoped, therefore, that the very condensed notes which follow will help to do away with the main bogeys of orchid culture.
The following kinds of cut-flower orchids can be successfully cultivated in this country by anybody who has at his disposal a glass-house: Cypripedium, Cattleya, Laelia, Brassavola and Epidendrum, as well as their numerous hybrids ; Dendrobium, Oncidium, Cymbidium, Vanda and Phalaenopsis.
The last two genera require rather high minimum temperatures during the winter (about 60°F.), and, apart from the warmer coast districts, must be grown in a heated glass-house. The rest thrive very well with minimum night temperatures of 50°F. and can stand occasional drops of temperature well below this margin ; depending upon, the local climatic conditions, they may or may not require heating during the winter nights. Certain genera from very high altitudes are particularly sensitive to heat and drought (e.g. Odontoglossum from the high Andes of S. America, Pleione from the higher parts of the Hymalayas and Yunnan) and cannot be given the appropriate conditions in our climate, except perhaps at high altitudes within the mist-belt.
ECOLOGY. With regards to their mode of living, there exist two main ecological kinds of orchids: (1) terrestrial or ground-orchids, for instance, Cypripedium (most species of the genus) ; and (2) epiphytic or arboreal orchids, which include all the others in the above list, except some Cymbidiums and a few Vandas.
This ecological difference must be considered in the cultures. Ground-orchids grow best in a porous compost consisting of a mixture of leaf-mould, pot-crocks or broken brick, and charcoal, to which some fibrous material may be added (coir or palm fibre). Epiphytic orchids, which in nature grow on the bark of trees or on vertical walls of rocks, do not like any earthy matter in their compost, which should consist entirely of fibrous materials such as fern-root (Polypodium or Osmunda) or other tough, durable vegetable fibre (coir or cocos-palm fibre) overlying a thick layer of pot-crocks or lumps of charcoal to ensure perfect and rapid drainage. At least one-third of the pot must be drainage which must be adequate to allow water from a garden hose at full pressure to run through the pot without overflowing.
The roots of most orchids, whether terrestrial or epiphytic, are encased in a sheath, the so-called velamen, which is sometimes very thick. It has several important functions to perform:—
(1) It firmly adheres to the substratum, or, rather, to any solid part thereof such as the bark of a tree. the walls of a pot, or the crocks in the drainage system) and can only with difficulty be detached from it ; this property allows even very heavy plants to stay firmly on the vertical surfaces they often occupy in nature.
(2) It readily absorbs any free or atmospheric moisture and retains it for the use of the plant, together with any soluble organic and inorganic- substances which may be dissolved in it. During rainless periods it is able to absorb sufficient moisture from the mist or dew to keep the plant alive and well.
(3) In extremely dry seasons, it protects the root itself from drying out.
In most epiphytic orchids we find various contrivances for the prevention of loss of water through evaporation, or for storing a reserve of water, or both: leathery leaves, thickened shoots or "pseudobulbs." Consequently, an orchid can stand long periods of. drought without any harm to any of its organs, unlike most other plants familiar to us (succulents excepted) which rapidly fade when deprived of water. This fact must be constantly kept in mind when cultivating orchids, and by far the greater losses of these plants in the hands of the inexperienced grower are due to overwatering than to insufficient water, disease or pests.
Another peculiarity of orchids (occasionally found in other plants such as conifers and heaths) is the fact that they harbour in their roots microscopic fungi without which they cannot prosper, as these fungi apparently are the only natural source of certain organic substances essential to the normal growth of the plants, and which the orchids cannot produce themselves. The dependence of the orchids upon the presence of these fungi manifests itself from the very earliest stage in the life-history. Orchid seeds, which are very minute and are deprived of anything but the barest minimum of reserve materials, are dispersed by wind ; if they manage to land on a moist surface of a tree or rock, or on a suitable bit of ground—all according to their natural ways of growth—they swell up and even turn green, but the development stops there, unless the hyphae (filaments) of the right fungus happen to be in very close proximity. In this case the fungal filaments penetrate the swollen embryo and curl themselves up inside one or more cells, with the result that there is a rapid increase in size of the tiny bead-like plantlet or "protocorm," which begins to develop absorbent hairs, then a first pair of leaves, and finally a real root. complete with velamen. This root, if not already containing the fungus (in some species the original infection is digested by the plant during the formation of the first root), becomes infected from the substratum, and from this time onwards the partnership or "symbiosis" of plant and fungus continues "until death doth them part." The orchid fungi exist in several distinct species or varieties, and are classed in the genus Rhizoctonia, some species of which are harmful parasites of certain plants such as potatoes and carnations. Some exceptional members of the orchid family associate with quite different types of fungi, such as the mushroom Armillaria, but all the orchids enumerated above have Rhizoctonia in their roots. The commonest species of Rhizoctonia is R. repens which is found in Cypripedium, Cattleya, Epidendrum (a relative of Cattleya} .Cymbidium and many other orchids. Another species, R. mucoroides, occurs in the roots of Vanda and Phalaenopsis, while a third, R. lanuginosa, is the symbiotic fungus of Odontoglossum, Oncidium and related S. American genera. The importance of the symbiosis has been proved beyond doubt. Certain investigators have tried to show that orchids can grow without it, basing their arguments upon the fact that it is possible to germinate orchid seeds under artificial conditions without the fungus, but in nature no orchid plant has yet been found which does not harbour a fungus in its roots, and asymbiotically raised seedlings do not progress in their development after they have been removed from the flasks with the nutrient medium, until contamination with the right type of Rhizoctonia has taken place. From that moment. development is greatly accelerated.
Correct cultivation of orchids therefore aims at providing conditions favourable to the symbiotic fungus, as well as to the plant itself. These conditions are
(1) high atmospheric moisture ; and
(2) alternating periods of moisture and drought in the substratum.
The first condition is fulfilled by spraying the floor, walls and spaces between the pots with water, as often as necessary to keep the moisture of the air near to saturation point, especially when the temperature is high. In colder weather it will be found that much less spraying will be required to saturate the air, and as the winter season coincides with the resting period in the growth of most orchids, the atmospheric moisture can be safely reduced.
The second condition requires more observation and skill, as the nature of the compost, the efficiency of the drainage and the amount of ventilation greatly influence the retention or loss of moisture in the compost in the pots.
The essential points to remember when cultivating orchids can be summarized as follows:—
(1) Provide for perfect drainage to avoid stagnant water and consequent root-rot, by filling at least one-third of the pot with crocks which are not too small, broken brick or lump-charcoal. When larger pots are unavoidable, two-thirds of the pot should be filled with drainage.
(2) Do not overpot: the smaller the pot, the quicker it dries out, and the lesser the danger of overwatering.
(3) Pot firmly, without impeding drainage: a loosely potted orchid does not root properly. Use a stake if necessary, driving it tightly into the drainage, and tie the plant firmly to it. See to it that no dormant buds or young shoots are buried below the surface of the compost, or they may rot away and stop further growth.
(4) Water only when the plant is in active growth (when new roots or shoots make their appearance and continue to grow), repeating only when the compost has dried: this can best be ascertained in the morning, as during the day the surface dries up quickly and may easily mislead the observer. One soaking a week is usually ample for larger pots (5 to 9 inches), but smaller pots may require one or even two more soakings a week, especially when they are hanging ; the same applies to hanging baskets which evaporate more quickly than pots. Overhead spraying of the plants is also helpful and partly replaces watering. Never water an orchid during its resting season as not only does it not need water but its roots cannot get rid of it and may easily rot. Remember always that with orchids it is more growth which requires more water and not more water which causes new growth. Use only rain water, as tap water often contains lime or chlorine and is usually too alkaline. Cypripediums and other ground-orchids can, however, tolerate tap-water because they often grow in nature on limestone rocks. Epiphytic orchids in nature live in places where no ground water can reach them and receive only rain-water which, particularly during an electric storm, is very acid and maintains the acidity of the substratum, a condition essential to their welfare. Do not spray overhead in the late afternoon or evening, as the plants will not have time to dry out before the night, thereby endangering young growth.
(5) Ventilate well: Orchids require plenty of fresh air, especially epiphytes which in nature invariably grow on trees exposed to the wind or in kloofs where a steady draft of fresh air is noticeable. Compensate for the loss of humidity by spraying the walls and floors. In very windy and dry weather reduce ventilation accordingly, also when the outside air is very cold. During the night, especially in winter, do not ventilate ; this helps to bring up air-moisture and prevents too much cooling.
(6) Give plenty of light, particularly during the resting stage: very few orchids can stand dark conditions for any length of time and many species require plenty of sunshine in order to flower. Some protection from the direct rays of the midday and early afternoon sun is provided by shades consisting of one-inch strips of wood placed at half-inch intervals over the glass-roof, preferably resting on a 4" mesh wire netting fixed well above the glass itself, to provide free ventilation between the shading and the glass, which helps to keep the temperature of the glass-house down. Although many orchids can stand rather high temperatures during the day, one should try to keep them below 90°F. If shading and spraying alone fail to achieve this, rather ventilate more: less harm will be done by dry air than by overheating.
It is well to point out that the task of the commercial grower is much easier than that of the private collector, because the former is concerned with the cultivation of large numbers of plants of fairly similar requirements, whereas the latter endeavours to keep as many different kinds of orchids as he can get. These often require radically different treatment, but he is compelled to grow them under the same roof.
A commercial grower in this country (except in warm coastal districts) could achieve best results with two separate glass-houses or with one divided by a partition into two compartments, one of which should be provided with hot-water heating. The unheated compartment could be occupied by Cypripediums and Cattleyas with their hybrids, with a separate corner allotted to Oncidiums which have a different Rhizoctonia) ; the heated compartment should contain Vandas and Phalaenopsis, which require more heat and have the same Rhizoctonia.
TRANSPLANTING. Generally speaking, orchids only need transplanting when. (1) they overgrow the rim of the pot, the new roots not being able to penetrate the compost ; (2) when the old pot is so root-bound that no further growth of roots is possible ; and (3) when a plant does not grow as well as it should and root-rot is suspected.
As the roots firmly adhere to the walls of the pot, care must be taken to reduce any damage to the minimum. The plant, pot and all, is put to soak in a tub with rain-water for about half an hour, which lessens the contact between the roots and the pot ; the roots are then carefully detached all round by inserting a flat knife (a table knife is the best) between the walls of the pot and the roots, until the whole ball is detached ; then, holding the plant with one hand and the pot with the other, the plant is held upside down and the pot lifted away. Any decayed or bruised roots should be cut off with a sharp knife or scissors and as much of the old compost removed as possible without damage. The new pot is usually chosen with a diameter sufficiently larger than the first to allow for two of three years of growth, but it may occasionally be of the same size as the first (when the ball has been somewhat reduced), or even smaller (when root-rot necessitates the removal of most roots and compost). The back portion of the plant is always placed as near as possible to the rim of the pot, thus saving space for further growth.
If all the roots have decayed, they must be all cut off at their very base and the plant treated as a cutting. All foreign growths (ferns, mosses) must be removed when transplanting and the plant carefully examined for pests (scale, mealybug, etc.). If these are present, they must be cleaned off with a tooth-brush moistened with water containing soap and nicotine or with methylated spirits containing some nicotine as well.
Transplanting may in some cases be avoided by removing as much of the old crumbling portions of the compost as possible without damage, replacing it with fresh lumps and renewing the whole surface as well. The practice of "surfacing" the ball with Sphagnum (as usually done in England), may be dispensed with or restricted to the smallest pots which dry off too quickly: the more frequent sprayings necessitated by our hot and dry climate may result in overwatering if Sphagnum is too freely used. After transplanting, especially if roots have suffered damage, the plant is given some extra shade, but it must not be watered for at least a fortnight, to give the roots a chance to heal and start growing again.
PROPAGATION. This may be done by three distinct methods. (1) Division: When a plant is spreading too widely in two or more directions, it may be of advantage to divide it into two or more parts, taking good care not to damage the roots. Each part is then potted up separately. This method is chiefly used for Cypripediums but may be occasionally used for other genera.
(2) CUTTINGS, (a) Back-cuttings: When transplanting, it is often found that the back portion, with two or three pseudo-bulbs, can be removed with advantage, reducing thereby any excessive length of the root-stock or rhizome of the original plant (as in Cattleya}. The sectioning is done directly in front of a shoot which has at its base a live dormant bud ; if kept under moist conditions, the bud will shoot and the new plant can be then potted up in the smallest possible pot. (b) Front-cuttings: When a very healthy and rapidly growing plant outgrows its pot, it is sometimes better not to transplant (especially when the original pot is already a large one). Instead, a portion including the foremost two or three shoots is cut off and potted up separately ; the remaining part will make one or two new shoots from the dormant buds of its foremost remaining pseudobulbs. It is very important to remember the right time for either transplanting or taking cuttings: it must be always done at the time of the appearance of new roots or new growth on the old ones, before these new roots become too long and run the risk of being damaged. As the roots of cuttings may lack the Rhizoctonia, a chance should be given them to acquire it, by planting them in a compost from a vigorous plant of the same genus.
(3) Sowing. This is a method which requires much skill and patience, but at the same time is the only way to acquire a large number of plants with the least expense, or to produce new varieties or hybrids. Orchids may be raised from seeds by two methods:
(a) The symbiotic method. This is the natural method, wherein the appropriate fungus enters the seed. In its simplest form, this method consists in sowing the seeds on the surface of the compost in a pot containing either the mother-plant or a plant of the same or related species ; this method is even now used for Cypripedium, but is not very productive, as the chances of germination are limited to a few favourable spots near the roots, and the seedlings are exposed to many dangers, particularly from insects and other pests which may be present in the compost. A better method consists of sterilizing a quantity of compost (by heat) and infecting it with the right Rhizoctonia by placing in it pieces of roots of species similar to those one wishes to sow. The presence of the Rhizoctonia may be ascertained by microscopic examination. or if this is not practicable, by carefully examining the terminal inch or two of the roots: if orange-yellow or reddish-yellow areas are visible in a section, the fungus is usually there. The root-portions are then well scrubbed with a brush under running water and rubbed with methylated spirits, to remove any surface dirt and contamination, and, after cutting them further into smaller pieces, are introduced into the flasks or jars with the sterilized compost ; the fungus, it present, leaves the root-pieces and spreads over the surface like fine spider-webs, many filaments creeping up the walls of the glass-container, where they can be examined with the aid of a lens. When the compost is well-infected (in about three weeks' time), the seeds are sown over the whole surface.
A still better method is to isolate the fungus from a young germination and grow it in a pure culture, and use this to infect previously sterilized flasks with compost. Success is assured in this case, and often a very large percentage of seeds germinates.
(b) The asymbiotic method. This method can only be used by somebody who is well acquainted with laboratory practice, as the whole work must be done aseptically (i.e. without any contamination whatever) from collecting the seeds to closing the flasks after sowing. The method is applicable to certain types of orchids including Cattleya, and the seeds germinate 100%. The media used are solutions of nutrient salts such as Meyer's, Pfeffer's and many other "water-culture" solutions, with the addition of plant-extracts (potato-extract, tor instance) and about 2% of sugar (cane-sugar, glucose or fructose), solidified with 1.4% agar-agar in a position to give a sloping surface. The flasks with the media are sterilized on several consecutive days (at least three) to kill any spores of fungi or bacteria, and allowed to stand for a week or ten days to make sure that no contamination is present. A small lump of seeds is then carefully introduced with a sterile long-handled needle flattened at tip, and after replacing the cotton stopper, the seeds are spread over the surface by the condensation water which is usually present and which is made to flow over the surface by tilting the flask in different directions ; in this way, a very even distribution of seeds may be achieved. As an orchid pod may contain many tens of thousands of minute seeds (in some species about quarter of a million), the numbers of seedlings raised by this method are practically unlimited ; but, as was stated above, the method can only be useful in experienced hands, and all modern orchid nurseries in England and elsewhere have invariably a small laboratory attached, where the more difficult processes of seed-sowing are done by experts. The rather high extra costs of keeping trained laboratory personnel are amply repaid by the results obtained.
The seedlings reach a height of from half to one inch within the first season, with three or four leaves and as many roots, and if too crowded can be taken out of the flasks and planted in trays or pots, containing finely chopped-up compost, which in case of asymbiotic seedlings must be infected with the right Rhizoctonia by simply adding to it some compost taken from a well-growing adult plant of the same or related species. As soon as the seedlings have formed good-sized roots, they are potted out singly in very small pots. It is well to place pots or trays with seedlings out of reach of pests, particularly slugs and cockroaches ; a good method is to place the trays, etc., on inverted pots standing in saucers full of water and cover them with sheets of glass during the night, the usual time for depredations of the abovementioned pests. The same general rules of cultivation given for adult plants also apply to seedlings, with the only difference that they may be kept on the whole more moist and given less rest, to speed up their growth. Under best conditions, orchid seedlings reach flowering size in from three to five years from sowing ; Cypripediums and Phalaenopsis grow quicker than Cattleya, some of the hybrids of the latter genus taking seven years or more to flower.
In conclusion, may I express the hope that the present notes will prove of use to all present or prospective orchid-growers in this country.