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Chapter - 03

The Rules Of Orchid Culture

There is no cultural difference between orchids and · other garden plants. All green plants have five basic growth requirements: air, sunlight, warmth, food, and water. Cultural divergencies among plants are not qualitative, only quantitative. For example, fuchsias require less sunlight, less food, and more continuous soil moisture than zinnias; but like zinnias they can take considerable warmth and need plenty of fresh air. The same growth factors are basically necessary to both plants; it is only the proportion in which these factors are combined that creates a different culture.

So also with orchids. They must be given these five factors in certain definite proportions which are, however, considerably different from those most other plants receive.

There has never been any secrecy about this or about the correct combination of growth factors that orchids require. Many excellent growers have given repeatedly exact and accurate instructions since the days of Sir Joseph Paxton. But they, like most of us who continue to regard orchids as something out of this world, have bumped their noses against the "system" of orchid culture. This system is obsolete, to be sure, but enough of it hangs on today to make it the greatest stumbling block to the popular cultivation of orchids.

In the beginning, orchid men were too often trained by rote. Certain practices were known to be successful, so the procedures were committed to memory. In this respect, Kew Gardens—otherwise so justifiably famous in the horticultural world—was the greatest offender. Having the status of a university for its gardener training program, and no competition, it taught apprentices by commandments. Men were not taught about their plants; they obeyed mechanical orders: water this house, dry that one out, open those ventilators two inches and close them at three o'clock. After all, these were the conditions under which orchids grew successfully at the Gardens. As soon as the apprentices were indoctrinated in the routine, jobs were found for them. Plants under their care then languished or flourished in direct proportion to the similarity of the new conditions to those of the place in which they were trained. Witness the lamentable complacency of the not uncommon remark: "So-and-so can do cattleyas, but he can't do cymbidiums"; or, "He may be able to grow cypripediums, but he can't keep vandas alive."

In other words, these men had a system and the conditions had to fit it for success. Whereas, the approach should have been: Accept the conditions you find and build them into a system. Make it an absolute necessity to know (1) the conditions your orchids require; (2) the conditions of the locale where you intend to grow them; (3) then adapt the latter to meet the minimum requirements of the former.

RULE NO. 1

Provide orchids with usually not less than 40 per cent and usually not more than 70 per cent atmospheric moisture (relative humidity) during the day.

While most plants get along on a definitely predetermined modicum of growth factors, several have eccentricities which should be pampered a bit. The eccentricity of orchids is that they require more atmospheric moisture than many other plants. Orchids are dependent on humidity owing to their strange, evolutionary adaptation to their native climate. Our familiar garden plants control water evaporation, known horticulturally as transpiration, by means of stomata, the microscopic leaf pores through which water evaporates into the air. Their stomata close in the evening, open in the morning. They are reduced in size on hot days, closed during dry spells. The stomata of most plants regulate or conserve the passage of water through the plant tissues. They keep enough water in plants so that the foliage is distended; yet enough water is transpired to provide plants with a continuous supply of soluble mineral nutrients.

Not so with orchids; their stomata are fixed, are perpetually open and thus continuously lose water. They cannot regulate the process. Nature does it for them. Atmospheric moisture slows down or prevents water evaporation from orchid leaves depending upon whether the moisture content of the air is low or high.

You have seen this phenomenon many times in your home. Place a glass of water in your living room; in a few days it is empty. Put another glass of water in your kitchen or bath; it lasts for weeks. Steaming foods and steaming bathrooms create enough moisture in the air to slow down evaporation from the glass of water. That is why plants frequently grow wonderfully in kitchens, fail in other rooms. All plants are benefited by some atmospheric moisture—orchids most of all.

In a totally dry atmosphere orchids lose water so fast they cannot maintain a reserve. They slowly shrink in size, wrinkle and die. Dry spells in nature rarely last longer than two weeks to two months. Usually there is some dew and soil moisture available to tide the plants over, yet they shrivel badly until the rainy season renews their growth and vigor.

Under the artificial conditions of home, garden, and greenhouse culture, orchids must be supplied with atmospheric moisture. It may be a small and continuous amount, or a relatively large amount during the day and little or none at night. Humidity is built up by several simple methods. The floors of greenhouses or the bases of Wardian cases and cold frames may be sprinkled daily with water. Garden walks, terraces, porches, and other outdoor areas may be hosed down as necessary to keep the air moist. In window culture, orchids are set above trays of water, moist gravel, or wet asbestos. If trays are inconvenient, orchids may be syringed once or twice daily with a small atomizer, or their leaves wiped with a soft, moist cloth.

These last two methods do not regulate transpiration; they check it, giving plants an opportunity to utilize water and build up a minimum reserve. Incidentally, all orchids, excepting a few water-sensitive ones, are benefited by syringing daily in clear, bright, warm weather. This is particularly true in eastern states. Of course, you wouldn't syringe orchids on dingy, dull, and cold days; or late in the afternoon or evening. It is almost axiomatic in orchid culture that the moisture in the air about the plants must increase as the temperature increases, decrease as the temperature decreases. In cold weather very little humidity is needed, if any; low temperatures prevent plants from transpiring water rapidly.

Although continuously dry air is fatal to orchids, they are benefited by a drying-out period once each twenty-four hours. In cultivation, this practice follows closely the pattern established by nature. The tropical morning sun quickly dries out orchid foliage before the daily rains appear and the air again becomes humid. Open up your orchid cases, windows, and greenhouses; let the air inside dry out for twenty minutes or so. How far you open your ventilating system, and how long, depends in great part on the weather. Low temperatures will shorten or prevent a drying-out period. After drying the air, close, or nearly close, your orchid structures and allow the humidity to build up again gradually. This variation in humidity, from little to much each day, helps to keep orchids working for their food, helps harden their growths.

How much atmospheric moisture can you give orchids? Well, here again two of the botanical classifications will help. Monopodial orchids require a high moisture content in the air, 70 per cent, particularly if they have thin, wide foliage; those with thick, leathery leaves can do with less. Sympodial orchids do not need such extreme humidity; 40 per cent will ordinarily suit them fine. And, if they are terrestrials, they are likely to be able to withstand little or no humidity except on hot days.

Humidity is a relative condition. Injuries caused by too little or too much are not always immediately noticeable. Humidity above 40 per cent is not in itself dangerous, but the moisture on cold days or at night may condense on glass and wood, dripping onto the orchid foliage. Cold drops of water then may cause decayed spots which are easily subject to bacterial infection. Little or no humidity causes leaves to wilt, producing first a slight wrinkling and later a distinct yellowing. Consistently high humidity develops soft, tender growths and saps the vitality of orchids.

RULE NO. 2

Orchids must have an abundance of fresh air at all times.

Orchids still are called air plants by the uninitiated who, accepting the fact that orchids weren't parasites and not bothering to check their root habits, suspected they had some miraculous mechanism for absorbing food from the air. Actually, all horticultural plants may be called air plants; for carbon dioxide, which they extract from the air, is the primary building block around which they construct their complex organic foods. Orchids can utilize carbon dioxide more efficiently than many plants. One of the reasons they thrive in trees is the abundant fresh air available there. Terrestrial orchids, too, are never found in thick undergrowth, but in open areas where air circulates freely.

In their native habitat many orchids are likely to be found where the air is cool, buoyant, and somewhat moist —but rarely saturated except for short intervals. Such air frequently is balmy and relaxing but with a quality that invigorates. This is the condition you must reproduce under artificial culture. It cannot be duplicated, but it can be simulated on a small scale closely enough to coax orchids into a state of well-being.

In outdoor gardening there is little to worry about if the air moves easily around the plants and is kept moist on warm days by evaporation from soil or other suitable material that is occasionally wet down. Usually, orchids grown outdoors for summer culture are set above the ground on inverted pots in order to insure the best air circulation and the most efficient use of air moisture. If drainage is excellent, potted terrestrials may be sunk into the ground.

Indoors, plant and human requirements for ventilation are essentially similar. A house that is healthy for humans is equally healthy for plants. If you possess a modern air conditioning unit that continuously circulates moist warm or cool air, depending on the season, the problem of ventilation is solved. However, most of us have houses which are often dry-heated to an unhealthy extent by steam radiators and gas fires. It requires a nicety of judgment to determine how much winter-chilled air a room can have without being uncomfortable. Let this be your guide: as long as a room has a clean, fresh odor it is suitably ventilated for orchids. There are few things worse for orchids than a musty, stale room.
 
The ventilation of cold frames, Wardian cases, and greenhouses is nearly automatic. Ordinarily they are heated, and air changes occur between interstices of the wood parts and through mechanical openings. Lacking a heat source, the tops of cold frames and greenhouses may be slightly opened on bright, warm days; closed later to conserve warmth after the inside air has been renewed. Air changes, even on hot days, should be slow in order to maintain reasonable constancy in temperature and humidity. Never pack orchids together; let them stand several inches apart in order to take full advantage of the air.

During winter, orchids should never be placed in cold drafts. In your home open an orchid window, if you must, from the top—not from the bottom, unless the incoming air can be warmed before it touches the plants. It is better to open a window in which there are no plants. Chilled air can freeze orchid leaves. They turn black at the edges, rot in the center. Hot air, especially if dry, causes leaves to wither and turn yellow.

RULE NO. 3

Orchids must have the maximum amount of sunlight they can stand without injury.

At one time it was presumed that heavily painted glass was necessary in order to protect orchid plants from sunlight. White or green opaque glass was used to simulate the darkness of tropical forests where, it was believed, the sky was nearly blacked out.

Not until well along in the nineteenth century did or-chidists begin to realize the inescapable part that light played in the growth and flowering of their plants. It was notable, even then, that orchids under dense shade rarely bloomed, a fact which supported the reports of scientific expeditions. In the Mexican mountains the May Orchid (Laelia albida) grows and blooms in full sun in rocky clearings; in the shade of near-by trees, it rarely blooms. Moulmein orchids of lower Burma grow on the tips of trees and are scorched by the sun; the orchids of Latin America are seldom completely shielded by tree leaves. The February, 1945, report of the Missouri Botanical Garden demonstrates that many so-called shade orchids flower better in sun.

Of all orchids, those called the "Tooth-tongued" (odon-toglossums) are most likely to grow in shade. They limit their spread to the central portions of trees. Yet the shade they receive sometimes has a more luminous quality than our early summer sunlight.

The equatorial sunlight at noon falls in a nearly perpendicular line in the tropics; in the temperate regions it falls at a considerable angle. The greater the inclination of the sun's rays, the less brilliance they possess. The summer sunlight of temperate America is about 25 per cent less brilliant than the equivalent tropical sunlight.

The question then arises: if, in the states, we get less sunlight than orchids are used to normally, why not grow them in full sun? It is done occasionally. Old Belgian growers once exposed orchids to full sun. In California and Florida orchids have been grown experimentally in rich loam and full sun with considerable success. Gravel-culture orchids frequently respond well to unobstructed sunlight.

However, success with such experiments is the exception —not the rule. Somehow the experimenters stumbled on the perfect growth balance that exists between a plant, the light it receives, the nutrients it absorbs, and the temperature of the air in which it is kept. An excess or limitation of one of those factors can throw plant growth out of kilter. So little is actually known about the growth correlation of orchids that most of us would injure plants by unduly exposing them.

Since the effect of light on orchids is still largely experimental, it is wiser to try out all orchid plants. Give them a reasonably large and continuous amount of light—the light that passes through sleazy muslin is good for a start. Then gradually transfer them to shadier places until the correct light intensity is reached. The right intensity is simple to determine, for orchids quickly indicate their light preferences. Orchid leaves fade to a yellow-white in too much sun, become blue-green and fleshy in too much shade. The correct light intensity seems to be that which keeps the leaves slightly yellow-green and the foliage somewhat stiff and leathery to the touch.

RULE NO. 4

Orchids require protection only from frost and snow.

This does not mean that warmth is not necessary to all orchids, nor does it preclude the use of artificial heat in rigorous climates. It implies that man-made heat cannot compete beneficially with nature's stimulating warmth. Artificial heat is a temporizing and last resort.

Orchids are hardier, more resistant to cold, than is popularly recognized even today. Epidendrum frigidum is always found where snow is a constant companion. The orchids of Indo-China often are covered with hoar frost in winter. Many Mexican orchids are subjected to sub-freezing temperatures in the Sierra Madre del Sur mountains. In the orchid country of the Andes, temperatures as low as 20° F. are not uncommon. Many of these orchids, in culture, have withstood consistently low temperatures, 32° F. and less, if the air and the potting compost are dry at night.

On the other hand, a few orchids—those from tropical lowlands—would quickly die if exposed to mild cold. They require higher temperatures. Fortunately, not many of these are worth the trouble of growing. Also, many orchids from below the equator are not adapted to our seasons; our winter is their summer. For them, some sort of artificial heat is usually desirable. They may be wintered in cold frames, Wardian cases, terranums, and warm house windows. Such miniature greenhouse structures can be simply and easily equipped with thermostatically controlled microme heating units or infrared lamps, which automatically give heat and light when needed. Small greenhouses can use gas or oil heaters, hot water or steam systems.

Most orchids come from one of three climatic areas and, accordingly, are divided into three temperature groups: (1) cool orchids from the higher mountains; (2) intermediate orchids from the plateaus; and (3) warm orchids from sea-level countries. During the past century a temperature chart has been worked out for the three groups. The temperature levels maintained by orchidists today are nearly 40 per cent lower than those once thought to be necessary —and are still dropping. At present these are the accepted minimum optimum temperatures for each climatic group:

Cool orchids,                            50° F.

Intermediate orchids                 55° F.

Warm orchids,                          65° F.

Learn to grow orchids at not less than these temperature levels before you experiment with lower ones. The maximum temperatures are not given, since all orchids, except one genus, the cool odontoglossums, can withstand high temperatures if they are fed well and supplied with abundant humidity during the day. All orchids are harmed by high night temperatures, which weaken them, making them easy prey to diseases and rots. Preliminary experiments by Lloyd Cosper indicate that orchids should be grown under fluctuating day-and-night temperatures. A difference of 20° between day and night is not too much. Fluctuating temperatures help to harden growth, stimulate the internal chemical changes which initiate new growth and flowers. But sudden extremes of heat and cold are not advisable for orchids under artificial culture. They will work better for you if they aren't overworked. Make temperature changes gradually. When in bloom orchids may be placed in a slightly cooler and drier atmosphere and more even temperature; the flowers will last longer.

You can keep a temperature check on orchids by noting their responses. Cold slows down growth and may cause the leaves to become brittle. If the plant freezes or if frost is too severe, the leaf tissues may be ruptured, developing soft, watery brown-and-black spots. Consistently high temperatures cause weak, rapid, immature growth. Growth is thin and slender, the leaves become soft and flabby, and the rhizome can't hold the pseudobulb erect.

Most beginners in orchid culture will be perplexed by the problem of supplying orchids with artificial heat. The subject still is debatable. Climatic conditions from California to New York vary so widely that a solution for one area leaves the problem unsolved for the next. The only consistently logical approach is to realize that orchids must be protected from extreme and continuous cold. Grow your orchids as cold as is compatible with their health. The closer you can imitate natural conditions without using artificial heating devices, the more successful you will be, the less labor your plants will require, and the more sturdy will be their responses. More damage is done by heat than by cold.

RULE NO. 5

Orchids must be fed. They must have a sufficient supply of continuously available mineral nutrients.

Many old-timers of orchid culture have only one comment to make on feeding orchids: "When elephants can climb trees," they say, "then we'll feed orchids!" Of course, this attitude doesn't refer to terrestrial orchids. For nearly a hundred years guano, fish meal, and barnyard manure have been added beneficially to the composts in which terrestrial orchids were grown. The quibbling about feeding orchids is now confined to epiphytes—those which grow on trees.

It was once assumed that large masses of decaying vegetation on the forest floor released ammonia gas which was absorbed from the air by orchid roots. This belief was demonstrated by Liebig to be absurd, yet early gardeners sprinkled manure water on the floors and walls of their orchid greenhouses, or put teakettles of manure water to boil on stoves. All they succeeded in doing was to make their greenhouses smell like barnyards. The few intrepid growers who soaked orchids with manure water found it often as dangerous to the plants as it could be beneficial. Roots tended to rot, and the foliage was easily burned.

Nevertheless, modern orchid scientists have demonstrated very precisely that orchids can and must be fed. The answer to the old difficulties is found in part in recent experiments which indicate that epiphytes have a low nitrogen metabolism. This is presumed because of their limited access to food supplies and their bulbous growths. Structurally comparable garden plants—irises, for example—are fed an increased amount of phosphorus, not excess nitrogen.

The original error in feeding tree orchids was in using a caustic liquid (manure water) at a greater concentration and with more free nitrogen than orchids could stand. The standard orchid compost of osmunda, a nearly sterile mass of dead fern roots, is not a buffer like soil. It cannot, like soil, protect roots from the action of caustic or unbalanced fertilizers until the osmunda decomposes. When it does decompose, the osmunda is no longer suitable for epiphytic orchids, for it waterlogs their roots. True success in feeding tree orchids is a relatively recent development—an outgrowth of water-culture experiments. Scientists have compounded nutrient solutions which are balanced and nontoxic to all plant life growing in sterile gravel, or inosmunda and similar media, without the protective advantages of soil.

The symptoms of malnutrition in orchids are not yet completely understood. These symptoms seem to follow the same general pattern in orchids as in other garden plants. A lack of nitrogen stunts growth and causes leaves to become yellow at the tip. Excess nitrogen produces rapid, soft, and flabby growth. Insufficient phosphorus frequently causes a brownish-purple discoloration which must not be confused with the slight purplish cast in some orchid foliage. Insufficient potash turns the tips of the leaves yellow and the edges scorch and die. The difficulty in diagnosis is the slowness with which these symptoms may appear, if they appear at all. The pseudobulbs of orchids are extraordinarily efficient storehouses of reserve food.

These are the fundamentals of orchid culture—humidity, air, light, protection, and food. The corollaries of composting and watering depend upon them and are manual processes which may be suited to your convenience. But don't try to change the rules governing the basic needs of orchids. Orchids are tolerant, but they have certain minimum growth requirements which must always be taken into account.

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