There are more ways to grow Cymbidiums than there are Cymbidium growers, because many ways have yet to be dreamed up. When deciding on your method of cultivation, a number of factors need to be taken into account. In Johannesburg we live at about the same distance from the equator as the major natural habitats of the Cymbidium species in the foothills of the Himalayas and in Vietnam. There are, however, some large differences in the climate. The large chain of mountains incorporating some of the highest peaks on earth, which constitutes the Himalayas has a very special effect on the climate which cannot be reproduced elsewhere. In winter the the south-bound winds which blow off the high Tibetan Plateau, are subject to the adiabatic effect as the air falls into North India. This effect dictates that as air falls, it slowly compresses, which causes its temperature to rise, so that by the time it reaches the habitats of the Cymbidiums, below 2600m, the air is above freezing point, which means that only the lightest of frosts are likely to be experienced in the highest natural habitats of the Cymbidium. During the summer monsoon, the moist air pouring in from the Indian Ocean to the southeast, produces very heavy and continuous cloud, limiting the maximum temperature. The high humidity of the region, a result of rainfall of over 300 cm (120 in.) per year, reduces the drying out of the environment during the dry season, providing a general moistness which is hard to reproduce.
In Johannesburg, in order to give Cymbidiums reasonable growing conditions we need to give shade, attempt to moderate our more extreme temperatures and attempt to raise our ambient humidity, which can go down to 5 % rh. in winter.
A most important factor to consider is why we are growing Cymbidiums. Here there could be a number of answers. Do we wish to grow for the show bench, or perhaps awards, for cut flowers to sell to florists, to raise potplants for sale, or pot-plants for our own pleasure as a seasonal interior decoration item or even because we are interested in Cymbidiums as plants, biological organisms or historical items? Ultimately there are two ways of raising these plants as seasonal growers or as continuous growers.
The Dean of Cymbidium breeders, the later Mr H.G. Alexander of Westonbirt in Gloucestershire, England, grew his Cymbidiums as seasonal plants in plain osmunda fibre, without feeding. By this means he kept his plants small, with modest bulbs, neat upright leaves, neat spikes of relatively few flowers, with less than annual flowering, and he considered large bulbs and coarse foliage to be extremely unattractive. By the early 1960s he was becoming quite vocal about people who grew Cymbidiums out of character by feeding them too much. He won many awards for his plants for two reasons. Firstly, he had bred the best material available in the world to put forward for awards and secondly everybody else grew their plants the same way.
At the other extreme, today's cut flower producer, for economical reasons grows his plants continuously, not allowing a seasonal slow down in growth as far as possible, he feeds like hell, he grows his bulbs and foliage as large as possible, he aims for a large number of spikes per bulb and per plant, every year, with a maximum number of flowers per spike, so that he may sell the large, coarse, often shapeless, cabbage-like blooms individually to a public who have as much taste as a barmaid. The demand is there: the grower must comply. I admire these growers in a perverse sort of way. Another factor to bear in mind is the finances of the grower, and how much he wants to lavish on his plants. The more one wishes to alter the natural weather pattern, the more one needs to spend. Export quality blooms need to be large, clear-coloured and unblemished and in order to produce these one will need excellently planned and built controlled conditions in a greenhouse, with first-rate day-to-day management. This requires a lot of financial outlay for buildings and equipment.
A much cheaper option is growing plants outdoors under shade cloth. This is quite practical as long as one is prepared to accept some cold damage to the flowers on occasion. Under these conditions one can afford to raise large blocks of seedlings, the best of which will be plants that perform well under your very own conditions.
Most people fail to appreciate the wonderful variety of plants and flowers to be found in the genus Cymbidium. This in some part was due to the old insistence by the judging fraternity that Cymbidiums must be large and round.
Let us now look at some of the factors that need to be examined when considering cymbidium culture:
Temperature: There are many aspects of temperature which need to be considered. When cymbidium tissue rises above a temperature of about 30 °C, the plants begin to respire faster than they can photosynthesize which means that they use up food supplies faster than they can manage to make food. 30 °C should therefore be one's maximum desired temperature. In the northern hemisphere, 26 °C is considered by many to be the ideal maximum temperature. The absolute maximum temperature which can be endured for short periods ranges up to the high forties. This was recently experienced at Duckitt's Nurseries at Darling in the Cape and apparently relatively little damage occurred. This temperature tolerance can probably only be applied to the leaves; the roots are likely to be considerably more heat-sensitive. Exposed pots receiving late spring and autumn direct sun in the hottest part of the day are likely to show considerable root damage when turned out.
As far as minimum temperatures go, the roots of a cymbidium tend to shut down and become dormant at temperatures below 12 °C. If one is determined to maintain continuous growth in one's Cymbidiums, one must see this as an absolute minimum. In the natural habitats, however, a light frost of 1°C is frequently encountered, but here the plants grow seasonally, having a growth period and a rest period. Most Cymbidium plants and flowers will take 1 °C minimum completely without damage. Below this temperature signs of damage may start occurring. Hybrids containing genetic material of Cymbidium erythrostylum are the most susceptible and can show bud and flower damage at -2 °C. Plants having a physiology driven by the genetic material of Cym. hookerianum (grandiflorum) and Cym. lowianum can take up to -7°C before damage is noted. In Robindale where I live, although I am in one of the warmest areas of the Witwatersrand, on a north facing slope, in some years temperatures of 3 to 4°C are experienced on one to three nights during the year with some resultant flower damage. My large collection of mostly seedlings in Kommetjie on the Cape Peninsula is fortunately only about 1 km from the sea and as a result of the buffer effect of this body of water at a constant 12 °C, the temperature never appears to go below 0°C and no cold damage occurs. Depending upon one's requirements and one's actual minimums experienced, various structures to house Cymbidiums can be constructed to modify the temperature, varying from a shadehouse with or without plastic or fibreglass cladding applied in winter to a properly controlled greenhouse. For those with only a plant or two, these can be grown under a peach tree and carried in under shelter on the coldest nights of the year.
In places like coastal Durban, Florida in the U.S.A. and in warm greenhouses, one may see excellent growth on cymbidium plants, with no subsequent flower production. It has been determined that during the spike initiation period, which appears to be around October and November in the Southern Hemisphere, one requires an 11 °C drop between the average day and the average night temperatures for spikes to be formed, something which does not occur in Durban, Florida or many greenhouses. A new class of Cymbidium hybrid, bred from the species Cym. ensifolium, a denizen of the warmer regions of China, Taiwan, Malaysia and Indonesia has been bred recently and this class of hybrid is called the everblooming. Examples of such hybrids are Cym. Peter Pan 'Greensleeves', Cym. Golden Elf, Cym. Valerie Absolonova etc., and they are being bred by Milton Carpenter of Everglades Orchids in Florida, U.S.A., amongst others. To keep these plants blooming, however, one needs a minimum temperature of about 15°C, so they are true greenhouse plants in our growing area. I have had a plant of Cym. Peter Pan 'Greensleeves' for about seven years under shadecloth in Robindale, and it has yet to flower. These plants are successful under warm conditions because they do not need the 11 °C temperature drop over the day for spike initiation.
Light: It is possible to measure light with a light meter. This is not something that I have done, so I can claim no expertise in this area. Both in Johannesburg and Cape Town, I use 50% shade cloth to moderate the light as well as the temperature. It appears to work well in both areas.
As a rule of thumb, it can be said that a plant which is light green with a hint of yellow is receiving an adequate amount of light. There is also, however, a close correlation between leaf-colour and feeding to complicate the issue. Another guideline is to give as much light as possible, short of causing leaf-burn. In Cape Town, my plants are a shade or two yellower than they are here in Johannesburg, partly as a result of the very long, very sunny summer days experienced in the Cape, and yet I only get sunburn of leaves in Johannesburg. Humidity may be an associated factor.
I have seen people giving their Cymbidiums much less light than I do and yet still grow and flower their plants very well, using up to 70% shade cloth. Too little light causes the production of soft, dark green, overlong leaves, and reduces the floriferousness. In our climate where temperature differential cannot easily be blamed for lack of flowering, this is usually due to too little light.
Water: The amount and frequency of watering, in a great measure, relates to the medium being used. As a basic rule it may be said that cymbidium roots do not appreciate being dried out completely. This probably causes dormancy of roots and root-tip shutdown and after such an incident a period of time is required to start them up again. As far as growing medium is concerned there are two basic classes; those that break down and those that do not. In the former, bark is the most usual ingredient. Bark has a good life of about three years whereafter it becomes an unsatisfactory growing medium. It is easier to grow in bark than in a medium which does not break down, and bark is particularly suitable if one chooses to grow Cymbidiums seasonally. When using a bark-like medium it is important to remember that the bottom of the pot must never be allowed to dry out. As the bark ages, however, it tends to hold more water, the air spaces become smaller due to compaction and roots filling these spaces and the deteriorating bark and natural dying off of roots use up more oxygen. As a result of this, watering must become less frequent. The drying out of the pot is necessary to allow fresh air to be drawn into the medium. A basic rule of thumb with regard to watering is to water plants today if you think they will be dry tomorrow. Remember to change the bark after about three years.
If you intend to grow continuously in a medium that does not break down such as rockwool or river sand, the problem of progressive anaerobia of the medium does not arise, but frequent watering is needed, together with careful feeding with chemical fertilizers, as the medium cannot supply any of the mineral salts required by the plant and it has no buffer capacity. It is very important not to mix any material that does break down into a medium, as this will result in an anaerobic state in a soggy medium; a fatal combination. Should anyone wish to grow their plants this way, please read up everything that has been written about the subject and consult with someone who is using this technique successfully.
Air: Ventilation and air circulation is of great importance to the plant as it not only helps moderate the temperature but it also brings new air, rich in the important plant food carbon dioxide.
If one grows out of doors under shade-cloth good circulation of air is supplied automatically. Do remember to leave some space between pots to enhance the upward circulation of air as well. If you grow under closed conditions mechanical means of assisting ventilation of fresh air from the outside, as well as air circulation within the house will have to be provided.
Humidity: A notable characteristic of the natural habitats of the Cymbidium species is high humidity all year round. This is not easy to supply in Johannesburg especially when growing in the open. Wetting down under the benches can help, but unless one grows in closed houses this will always be a problem here, although not a fatal one despite the fact that our relative humidity here in August can fall to 5 %.
Feeding: There are at least as many ways of feeding as there are Cymbidium growers. At both my collections Multifeed P is used, at the rate of one teaspoon per 20 litres, at just about every watering in summer and at every second or third watering in winter and the results seem to be adequate for my purposes. Plants can, of course, be fed much more than this, the more you feed, however, the more careful you have to be with the N:P:K ratios in different seasons. The basic adjustments include increasing the nitrogen from December to April, increasing the phosphorus for the rest of the year, and giving high potassium while the spike is developing.
Some people advocate the use of slow-release fertilizer pellets and if you wish to go this route, speak to someone who has used it successfully. Various slow release nutrients can be added to the medium, as discussed in the next section.
Medium: I use bark as my basic medium. In Johannesburg the formula is two bags fine, two bags medium and one bag coarse. In Cape Town we use one bag of coarse to one bag of medium, because the humidity is higher. In both cases we add polystyrene granules, at a rate of about 25 % of the total medium. Some people feel that polystyrene is environmentally unfriendly, but I have found that it breaks down fairly easily when exposed to ultra-violet light and I like the larger surface area that it provides in the medium.
In Cape Town we add about one and a half litres of local lime chips per bag of bark used to supply some calcium and that is our complete medium there.
In Robindale we add about one litre of dolomite chips per bag of bark plus half a litre of imported peat, which helps to hold some moisture initially in the medium, this all washes out after a few months. We add half a litre of vermiculite per bag of bark which holds some water as well as absorbing some of the mineral salts in the fertilizer. We have found bone or bonemeal to be a good slow release fertilizer. The biggest problem with bonemeal is its fineness which means that most of it is probably washed out quite quickly.
Bone provides calcium, phosphorus and some nitrogen. Pieces of bone are ideal, but if in short supply a suitable substitute is six parts of bonemeal and one part of cement made into a mortar with water, granulated and dried. The cement supplies some additional calcium in this case. A piece of bone cement the size of a walnut is adequate for a six inch pot.
Pests and Diseases: Fungal and bacterial rots appear to enter the pseudobulbs via rotting roots in old brokendown medium. At the first sign of rot pull up and clean the plant and cut all rot out to clean, healthy tissue. Treat cut areas with sulphur, allow to dry for a short period and plant into dry medium, watering thereafter with great care.
Redspider: This pest causes millions of microscopic punctures in the leaf tissue and injects a toxin which stunts the growth. The best treatment is to feed and water the plants more and increase the humidity as the mites do not thrive on the dilute sap which the plants produce under these conditions. Spraying with an insecticide to treat another condition may often precipitate an outbreak of redspider as this insecticide destroys their natural predators.
Scale: This is a common problem. Two or three sprays, each two or three weeks apart of Chlorpyrifos appears to be able to keep these pests under control, but may precipitate a redspider outbreak. Spray only a small section of the collection at one time so that you have a reservoir area of red spider predators left untreated.
Slugs and snails: Use bait regularly and if this fails use attractants like potato slices on the tops of the pots and go out in the evenings and collect and kill the slugs and snails. Do not forget to inspect newly emerged flower spikes at this time.
Aphids: These normally only attack flower spikes. A very light spray with Pirimor aerosol on cloudy days or near sunset is usually sufficient to make them disappear.
Pest control is dependent on diligent observation of your plants as frequently as possible and rapid action when a problem is detected.
The Interconnectedness of things: In plant growing you are creating an artificial environment but it is still capable of having a balanced ecology. With observation it is eventually possible to see that all aspects of culture are related to each other. For example, a plant getting more light needs more food, more water, a higher temperature, all to balance out an ecological equation. Excessive problems with pests and diseases indicates that some other aspect of the culture is not right.
To finalise, it is interesting to point out that if you want to kill a cymbidium, use a seven pound hammer, because they are truly wonderfully resistant plants and it is hard to guarantee that you will ice them any other way.