Among cool orchids there is none superior to odontoglossums, whose name means "tooth-and-tongue," a reference to two small toothlike projections on their lips. The name was compounded to describe Odontoglossum epidendroides, a plant now unknown to science except for a preserved fragment placed in the Berlin Herbarium by the explorer von Humboldt early in the nineteenth century. Many claims for the rediscovery of Odontoglossum epidendroides have been made, but none has been substantiated. It remains one of the numerous lost plants of the world, a horticultural mystery.

There is no quibbling among orchidists over the strikingly beautiful flowers of this genus; in fact, there is not an insignificant or poor flower in it. The flowers, from five to thirty of them, are carried on elegantly arching stems; they vary in size from three to five inches. The colors are wonderfully clear and are blends of yellow, brown, and the brightest red and the lushest purple in the orchid tribe. Many of the flowers of Odontoglossum crispum, often called the "Queen of Orchids," are exquisitely and be-wilderingly mottled with an infinite variety of red, yellow, and mahogany on a background of pure white; no two flowers on separate plants are ever exactly alike.

This natural variation has made the crispum branch oí odontoglossums a headache to botanists and has produced confusion in their nomenclature. There are more varieties of species than of species themselves; natural hybrids outnumber their parents nearly a hundred to one. The plants, though, are conservative and uniform in appearance. They are moderate in size, with short bright-green pseudobulbs and short grass-green foliage. Their spacesaving qualities make them desirable where room is at a premium.
These characteristics may make the genus seem well suited to the fancies of beginners; but it is highly unlikely —under the present technique of culture—that you will be able to grow more than six species out of the hundred that are known. That's a phenomenally poor batting average when you consider that odontoglossums are among the hardiest of orchids—but the fact is that the strange hardiness of most odontoglossums is the cause of their cultural difficulties. Odontoglossums are the alpines of the Western Hemisphere; most of them cannot stand temperatures above 80°!

Odontoglossums are limited to the western mountains of tropical America from southern Mexico to Peru. Within this area most of them are again restricted to an average elevation of 10,000 feet and a rather unusual climate. Along this chain of mountains, odontoglossums are divided into two geographical sections which correspond also to their two cultural groups: the few Mexican species (easy to grow), and the many New Granada species (difficult to grow). The latter name is no longer scientifically desirable, but is kept because it is used commonly to describe odontoglossums inhabiting South America from Venezuela southward. The Mexican odontoglossums also are misnamed; they may be found in Guatemala and Costa Rica as well. In the area from Costa Rica to Venezuela, along the Isthmus of Panama, there are no odontoglossums because there are no mountains high enough to offer the climatic conditions they need.

New Granada species are most often found between 5,000 and 9,000 feet growing as epiphytes, although many of them may climb to 12,000 feet and grow on rocks or bare ground well above the timber line. At these elevations the average mean temperature is quite low: about 570 for the higher areas, 65° for the lower. The temperature variation between day and night is remarkably even. It rarely exceeds 15° both winter and summer.

Rainfall in areas in which the New Granada odontoglossums grow is excessive and the largest plant colonies are found in continuously moist locations. The air is highly saturated, a product of the moisture-laden trade winds. As a result of these conditions New Granada odontoglossums never really stop growing. In spite of the coolness and the rain to which they are subjected, these odontoglossums need plenty of sunlight. They are abundant where forests skirt streams. Many odontoglossums are found growing in full sun with healthy results. They may be slightly stunted, but they flower more heavily and consistently than those in semishade. In their natural environment they have fresh, moving air. Indeed, the air is never at rest; there is always a breeze and sometimes a gale.

On the other hand, the Mexican species aren't habitual mountain climbers. They live in the Tierra Fria of lower Mexico where the average elevation is about 5,000 feet. This tableland is drier and less humid than the corresponding odontoglossum country in South America. The summer temperature may rise to 90° or higher. The winter temperature may drop to subfreezing. The definitely marked dry season is from April to December, when it rains little if any. However, the trade winds drift over the area carrying air of high moisture content which condenses about the plants. So, while the Mexican odontoglossums do have a rest period, they still pick up enough moisture and dew to keep their pseudobulbs plump. These climatic conditions, and a predilection for semishade, make this section of odontoglossums amenable to culture in North America. One of them, Odontoglossum grande, has been acclimated successfully to shade gardens in southwestern and southeastern United States. It has been a common house plant in Holland for many years.

Actually, you now need no cultural instructions beyond the brief descriptions above of the two classes of odontoglossums. The culture of both sections is deducible readily from the climatic conditions of their native mountains. The New Granada species will need to be watched with all the exacting care you'd give a child going through its first training period. All the cultural factors are within your control except temperature, and that is the most important factor. The extreme heat of our North American summers interferes with the successful cultivation of New Granada odontoglossums. It is simple to heat a greenhouse in winter, nearly impossible to cool it in summer without overly elaborate equipment. One good hot spell and these odontoglossums don't recover. It's as simple and as fatal as that.

Since the limiting factor in growing New Granada odontoglossums is temperature, let's examine that first. Winter or summer the practicable minimum temperature is 45°; the maximum is 70°—occasionally 80°, but never higher. The variation between day and night temperatures should not exceed a difference of 20°. Most orchids withstand a wide temperature differential—but not odontoglossums. If you live in far northern states, on mountains, or your home or greenhouse can be equipped with modern—and very expensive—air-cooling units, your problem will be less acute, but no less important. However, as you descend below the 40th parallel of latitude the climate becomes increasingly mild for humans, and increasingly obstreperous for New Granada odontoglossums; summer is too hot for too long a period. So, if the summers in your town or country get as warm as 90° for several months—don't try to grow New Granada odontoglossums unless you are prepared to spend a lot of time and money on them. Even in mild sections of California where the climate is remarkably uniform in summer most attempts to grow odontoglossums have failed.

Greenhouses may be cooled as much as 10° by using certain shading materials. Build a simple frame of 1x1-inch or lx2-inch surfaced lumber about a foot above the greenhouse roof. When the thermometer in summer reaches 75° place a single layer of butter muslin over the frame. It stops heat rays and the air in the space between it and the roof acts as an insulating cushion. Some orchidists prefer wood roller blinds alone, but they permit 50 per cent of the sun's rays to touch the glass roof and appreciably warm it.

A very efficient method of reducing heat is to install sprinklers on the roof of greenhouses and operate them in hot weather in addition to lath shade. Recently a grower in Pasadena, California, installed a 4x4-foot packaged air conditioner to humidify and cool a small house of 500 square feet. The unit was capable of maintaining an inside temperature of 80° although outside temperature was 95°. When muslin shade was added the temperature was lowered another 5°. Unfortunately, most cooling systems dry the air and you must have additional humidification apparatus.

The type of greenhouse you use also may have much to do with your success in controlling temperatures. A north-south gable house gives equitable light but develops considerable sun heat. An east-west shed-roof house gathers even more heat and light, but if the shed-roof house faces north it gets less light and less heat. Knowing these simple facts, several eastern amateurs built an even-span greenhouse with its axis running east and west. Down the center they erected a wall of wood planking extending from ridge to floor, from one end to the other.

In effect they have two shed-roof houses placed back to back. During hot weather they transfer odontoglossums to the cool north house where a circulating fan keeps the air moving and a mist sprinkler keeps it saturated. Incidentally, a fan is almost a "must" in order to keep the air circulating. When the weather cools off they return the odontoglossums to the south house where they secure more sunlight and additional warmth. Two 1,650-watt electrical fan-and-heater combinations are used in connection with an automatic humidifier to keep the inside temperature at 45° although freezing weather is not unknown in their town.

The other cultural requirements for New Granada odontoglossums are just as strict as those for temperature, but are more easily controlled. The atmosphere must be nearly saturated (about 80 per cent) during the day, lower (40 per cent) at night. In winter the humidity may drop enough to avoid extreme dampness and excessive condensation. Failure to keep the air well supplied with moisture frequently results in debilitated plants. On warm, bright days plants must be syringed with water several times a day as well as maintaining atmospheric moisture.

Ventilation is sometimes baffling because air should be in motion; moving air stays fresh longer. Although they are harmed by drafts New Granada odontoglossums do not do well in stale and close atmospheres nor in hot, dry ones. In a commercial house with a large air mass it is possible to leave top and side ventilators open much of the year, admitting just enough fresh air to keep the house sweet and the air in slight motion but not enough to lower the humidity appreciably. This is impracticable in a small house. However, top sashes can be left slightly open and air circulated beneath the benches by electric fans.

As far as light is concerned, odontoglossums can go by the rule of thumb already established: as much light as they can stand without injury. Above the 35th parallel only light summer shading is necessary. Below this line it is often necessary to provide shade both winter and summer. In many cases orchid growers use a mixture of whiting and gasoline to paint greenhouse glass. In the small houses of amateurs butter muslin will do better; it provides a soft, luminous light very similar to that which New Granada odontoglossums are accustomed to receiving in their mountain homes.

You would be wise now to forget all that you've read about New Granada odontoglossums except in so far as it may be interesting. Don't try to grow them—beautiful as they are—unless you can meet adequately their minimum requirements. If you find, however, that you can't live without growing them, specialize in them only. Before you buy a single plant study their requirements in every orchid book, both ancient and modern. Next study the best books you can get on greenhouse construction and management; read the best books available on air conditioning. You would do well, also, to visit orchid establishments and get good information at first hand from growers who know the quirks of odontoglossums. Then, and then only, start raising the lovely New Granadian Odontoglossum crispum and its innumerable varieties.

For most of us who haven't a well-filled purse to back up an inclination or hobby, or the time, the Mexican odontoglossums are much easier to grow and just as lovely. They have essentially similar requirements to the New Granadi-ans but are more flexible about them. They can do with a great deal less humidity, are not injured by low temperatures, and can tolerate a good deal of summer heat.

Culturally they may be divided into two subsections: those which might be called semihardy like Odontoglossum ci· trosnum, and the hardy ones of which the exquisite Odontoglossum grande is typical.

For all practical purposes semihardy odontoglossums may be considered as having cultural requirements similar to those of cattleyas and laelias. The lovely Odontoglossum bictonense—the first of the genus to reach Europe alive—and the fragrant, violet-colored Odontoglossum krameri are frequently grown with cattleyas as companion plants. They are excellent casual subjects since their flower stems are pendulous, thus permitting them to be hung in baskets from the upper, often barren, portions of windows and small greenhouses.

The rest of the genus, the hardy odontoglossums, include only three species: Odontoglossum grande, Odontoglossum schlieperianum, and Odontoglossum insleayi, in the order of their importance. Except for size, the flowers of each are remarkably alike, most of them having chocolate-barred yellow flowers which bloom in time for Halloween and Thanksgiving. Oddly enough, these species usually do not do too well in greenhouses. They prefer semishade and moist, cool, airy terraces, lath houses, and rockeries. They are not injured by continuously low humidity although dry air should be avoided. Any one of them will do well in kitchen or living-room windows without any more pretense or equipment than merely being placed on a shelf. Syringe the leaves daily in warm weather and keep the plants out of direct sunlight after 10:00 o'clock in the morning. These three odontoglossums should find a place in every beginner's collection; Odontoglossum grande in particular is suggested as another plant house guest.

In propagation, potting, and composts all odontoglossums are treated alike. They are propagated by division of the pseudobulbs (never less than three); and are divided as soon as the root collar appears on new growth. Although called epiphytes, they are not always grown in osmunda. More consistent success is given by terrestrial composts. Many of the old growers of the last century were quick to recognize this and devised a compost of equal parts of finely chopped osmunda, live sphagnum, and leafmold with some coarse river sand thrown in to keep the mixture porous. Today lea£mold and fine gravel or decomposed granite provide an equally suitable growing medium. The only change in the formula previously given is to sift out the coarse parts of the leafmold. Odontoglossums do best in a fine, soft compost.

Select clay pots barely larger than the plants and half fill them with coarse gravel before you add your compost; odontoglossums have thin, short roots and don't require much rooting space. Firm the compost but don't tamp it; and don't worry too much about keeping the pseudobulbs above the level of the pots; they are used to lots of water. Nonetheless, don't let water stand over the rhizomes, or partly cover the pseudobulbs. Incidentally, many successful English growers top-dress the compost with a quarter-inch layer of live sphagnum. The green sphagnum is pretty to look at and acts as a mulch, keeping the compost cool and moist; also, when the compost soured, the sphagnum indicated it by dying. This is not a bad trick, but very misleading in America. English sphagnum requires little moisture, coming as it does from rather dry table-like plateaus; American sphagnum comes from swamps and in order to keep it alive, orchids get watered to death. Mulch odontoglossums in the United States with crumbly bits of peat moss, coarse sand, or fine gravel. Neither is it a bad idea to repot odontoglossums each year since they are grown in smaller pots than is. normal for most orchids.

Watering should be done with caution after potting and until the plants are established; thereafter, water as often as. required, though never excessively. In good health odontoglossums should never be without water at any time since-they are evergreen and never truly at rest. Even the Mexican, species require sufficient water between growing periods to· keep their pseudobulbs plump. The key to correct watering; during these intervals is never too much at one time; andi never a really dry compost.

There is some question about the wisdom of feeding odontoglossums if the compost has sufficient leaf mold in it. The best results in healthy plants and flowers have been secured experimentally from planned feeding programs. Most often they are fed only in summer when their growth rate is at a peak, but winter feeding will also pay increased dividends in strong plants. Many kinds of weak liquid fertilizers have been used successfully, though they must have something of a balance in the nutrients they contain. Startlingly good growth and heavy flowering have been secured by a combination of nutrient solutions and manure water. During winter only a nutrient solution is applied once a month; in summer it is increased to twice a month, and once a month manure water is given. The latter seems to give odontoglossums a tremendous boost, helping to keep their growth uninterrupted by providing them with many of the rarer organic salts and hormones they ordinarily receive in their native habitat.

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