GROWING THE NEW
'TEMPERATURE TOLERANT' CYMBIDIUMS
by Milton O. Carpenter
Cymbidiums are tops among all orchids for commercial flower sales throughout the world. Why is this? Because the plants are highly productive in terms of yield, easy to grow, and produce rather large, attractive flowers with excellent lasting qualities (on or off the plant). In addition, the colors and combinations of colors seen in our modern Cymbidium hybrids are the equal of those seen anywhere in the Orchid world. So, why aren't Cymbidiums cultivated by all orchid growers? Well, first of all, orchid growers differ greatly in their "tastes" and because Orchids are the largest plant family in the world, they have plenty of selection to chose from. The main reason, however, for lack of universal cultivation is the fact that almost all modern hybrids are derived from just seven of the large flowered Cymbidium species found principally in the hills of Nepal and Sikim, where they enjoy bright sunlight and cool days and nights. Successful cultivation then requires that we emulate these climatic conditions - which is easily done in California, Australia, New Zealand, and England and Holland (the latter two with greenhouses to protect from freezing in their Winters). Areas of the world without these naturally cool conditions have been usually unsuccessful in Cymbidium cultivation. About 30 years ago we saw a great interest in "miniature" cymbidiums, made by combining the species pumilum with various of the "Standard"(large flowered, cool growing), cymbidiums. While these plants were more floriferous and somewhat easier to bloom than "Standard" cymbidiums they were not reliable blooming plants for areas such as South Florida where we do not have naturally cool nights. Thus, our decision, 30 years ago, to embark on a hybridizing program, designed to create (with natures help) "temperature tolerant" Cymbidiums. We define these as Cymbidiums which will perform well in a temperature range of 95 F to 45 F and generally without the need of a wide temperature variation between day and night to initiate spikes. We recently saw some of our hybrids blooming at sea level in Tahiti, where the difference between day and night temperatures are quite small. From among 200 select breeding plants of "Standard" cymbidiums we found just four that would perform reasonably well in our semi-tropical climate and have used these principally in combination with: (1) Parishii 'Sanderae' from Burma. A beautiful pure white flower with red labellum, erect inflorescence, 10 to 12 flowers of 7.5 cm. natural spread, which blooms reliably once every winter and is somewhat temperature tolerant. (2) ensifolium and it's allied species from Ceylon, Assam, and Southern China. These are small plants and flowers with delightful fragrance (which is generally imparted to their progeny) and excellent heat tolerance. Some of these species like to bloom in the middle of our Summers when temperatures in our greenhouses reach 110 F daytime and 80 F at night. Hybrids involving these species and "Standard" cymbidiums usually bloom both Summer and Winter and occasionally all year around for us. (3) chloranthum, from Malaysia and Java (also reported from the Philippines). A very warm growing cymbidium producing up to 40 one inch luminous green flowers on each semi-erect inflorescence. We have however, only been successful in making one hybrid with this species so far (Cym. Nancy Carpenter). To the best of our knowledge, we are the only commercial orchid firm in the world to specifically develop a breeding program to produce "Temperature Tolerant" cymbidiums, but we do want to acknowledge the substantial help of one of the world' most knowledgeable Cymbidium growers, Mr. Andy Easton of New Zealand.
First, remember that all cultural factors are inter-related (for example, a significant decrease in light intensity will call for a corresponding decrease in water and fertilizer), and secondly, we know that climatic conditions vary from place to place, thus the individual grower should make those adjustments which allow him to obtain the best results under his conditions.
Probably the most important factor in the flowering of Cymbidiums. A good rule is to give as much light as possible, short of injuring the leaves. Proper intensity is indicated when the leaves are a grassy yellow-green color. Too much shade is the most frequent cause of non-blooming cymbidiums. If you have a foot candle meter, it should register 4,000 to 6,000 or more during the growing season. When the bloom spikes begin to form, it is a good practice to leave the plant in the same orientation to the sun, for we have found that moving a plant and changing this orientation at that time will occasionally cause the young spikes to blast. Later, as the buds begin to emerge from the spike sheath, rather heavy shade may be applied (which will generally result in clearer colors and longer lasting flowers. Too high light intensities at this time could cause sepal deformation and/or bud drop. As soon as plants have finished blooming, return to the higher light intensity.
Our "Temperature Tolerant" hybrids are tolerant of heat and also enjoy cool night temperatures (but do not require them). We experience daytime temperatures up to 110 F during our five Summer months and many of our plants are happily in bloom during that time. While most "Standard" cymbidiums require 20-25 F differential between daytime and nighttime temperatures during late Summer and early Fall to induce plants to start spikes, this is not required by most of our "Temperature Tolerant" cymbidiums.
During their most active growth period, March through September in the Northern hemisphere, cymbidiums require much more water, in fact, with good drainage (a necessity at all times) the compost should be kept moist. During the Winter months, cymbidiums should be thoroughly drenched and then allowed to become almost dry before watering again. Never allow the potting medium to become "bone" dry however! It is also a good practice to thoroughly leach the potting medium periodically to remove any excessive accumulation of salts. On bright summer days cymbidiums will respond heartily to misting of the leaves, which reduces leaf temperature through increased evaporation and humidity.
A factor often overlooked and of prime importance. City water and/or well water will many times be found to contain an unusually high total soluble salt content. Ideally, the soluble salt level should be 25-50 ppm (parts per million) but not more than 100 ppm. Rainwater is almost always the best source for good water, generally having a low soluble salts concentration and proper pH. One of the main causes of leaf tip die-back is too high a concentration of soluble salts in the water (the other main cause being simply a lack of water). In South Florida, most cymbidiums are grown out-of doors all year and benefit from the natural rains, especially during our wet summer months when almost daily showers are experienced (this fortunately coincides with our period of highest light intensities).
During the growing season (April through August here) use a high nitrogen e.g. (30-10-10) water soluble fertilizer at the rate of one teaspoon to a gallon every two weeks if in fir bark, or balanced e.g. (20-20-20) if in an inorganic media. There are a number of commercial fertilizers available now which combine a number of the minor and trace elements along with the major ones, all in one formula - these are recommended. Another alternative is the use of pelletized, slow release fertilizers which, placed on the surface of the potting medium release minute amounts of fertilizer at each watering. In Tropical and Semi-Tropical areas apply no fertilizer during September, and from October through March use a low nitrogen e.g. (10-20-30) water soluble fertilizer at the same concentration and frequency mentioned above. Always feed on bright sunny days, as plants cannot utilize the food in cold, overcast conditions.
Good air movement is a necessity at all times and the plants should be potted somewhat high in the pot to allow good air movement around the base of the bulbs. Depending on the individual growing situation it may be desirable to hang the plants from an overhead frame in order to provide the best air circulation.
There are almost as many different cymbidium mixes as there are growers but if you are using an organic mix it should be slightly acid (pH 5-6). Generally speaking, whatever is being used with success in your area on "Standard" cymbidiums will work well with our plants. Remember that the drainage must be good however, for while these plants require copious amounts of water during their growing season, they will not tolerate water standing around the roots. For the past several years we have been using "Rock Wool", an inert material made from molten, spun, rock. This is available in a 70/30 mix (water retentive/water repellent) and most recently Grodan 'Stone Wool" especially formulated for orchids has been used with good results (better roots and leaves). The obvious advantage to using this material is that it will not break down as does organic materials and thus can be left on the plant root system for a long time if particular attention is paid to "flushing" routinely for accumulated salts. When "potting up" from a smaller to a larger pot the entire root ball can be transferred to the new pot when in this media - thus preventing the broken roots and plant "shock" which normally results when trying to remove old organic media. If you use "Rock or Stone Wool" do not press down the media as this removes the natural air spaces which are between the fibers and which are beneficial to the roots.
Experience leads us to believe that plastic pots are best for these cymbidiums as they have better moisture retention, roots do not stick as much as with clay, there is practically no salts accumulation, and they are lighter in weight.
PESTS & DISEASES
Fortunately cymbidiums are more resistant to pests and diseases than are most orchids. Snails and slugs must be controlled, especially during the blooming season. Metaldehyde in powder, liquid and pellets are effective. Spider mites are probably the major pest. Its small size makes it difficult to detect and spray must generally be applied to the underside of the leaves (where it locates) for proper control. Kelthane, Cygon, Pentac, Avid, Vendex or Dimite may be used. Orchid scale can be controlled with Malathion or Cygon. Fungus diseases are seldom a problem; when they do occur, use Subdue or Aliette. A good preventative spray is Captan, Tersan or Kocide applied three to six times yearly. Cymbidiums along with most other orchids are subject to all virus diseases. Their spread can be controlled by proper precautionary measures such as destroying or segregating infected plants, sterilizing all cutting tools (a propane torch is good), and keeping insect populations at a minimum.
The best time to repot is after the plant has just finished blooming. Repotting is necessary when (1) the plant has reached the edge of the pot and there is no room for development of new growths or (2) the potting medium (if organic) is decomposed. If you are not sure of the health of the roots or condition of potting medium, take the plant out of the pot to examine closely. If the plant and medium are in good condition, with only a few leafless bulbs, you may want to shift the entire plant to a larger pot keeping the root ball intact. Division of the plant may be desired if there are several leafless back bulbs present. Keep each division to a minimum of three leafed bulbs, removing the back bulbs which you can repot individually to start new divisions. When repotting, allow enough room between the plant and edge of the pot for two or three years growth. After repotting, place plant in a shady, humid location and mist the foliage often, while curtailing the watering of the compost. This will encourage new root action, after which the plant is returned to normal light, food, and watering practices.