Orchid Growing Videos Search! Enter Your Topic Below:

Chapter - 10

Seed Germination

There are three methods by which you can increase your orchid collection. The simplest, and most expensive, is to go out and buy more plants. A cheaper method is to make propagations from your own stock. Some terrestrial orchids double their size each year, and many sympodials every third year. The cheapest method of all, and the one that is usually the most fun, is to grow orchids from seeds. But that does take special knowledge, frequently needs special equipment, and often requires more than the patience of Job.

Charles Darwin once estimated that if all the seeds produced in one season by a single Orchis maculata—a. native British orchid—germinated and grew, the progeny would fill an acre of ground. The next generation would cover every nook and cranny of the British Isles. And the following generation would blanket the earth with a green carpet of orchids. Therein is the significant clue to the difficulties of growing orchids from seeds. Nature has made orchids the most prolific seedbearers in the plant world. They produce so many seeds—anywhere from 200,000 to a million in each pod—that their seeds are immature, and so small it is often impossible to distinguish them clearly. Common plants, like marigolds and carnations, have seeds that contain minute plants ready to sprout when warmth and moisture are present. But not so with orchids; their seeds contain only a mass of undifferentiated protoplasm —the basic material of life—inside a tissue-like envelope. In nature a fungus, mycorrhiza, stimulates orchid seeds, providing them with food until the protoplasm develops cells and, later, roots and leaves. As the plants mature the fungus is digested, its usefulness completed. In artificial culture, a special technique is necessary, involving nutrient agar gels, cane sugar (which seems to make up for the lack of the mycorrhiza and its chemical excretions), and sterilized flasks.

This technique, called the nonsymbiotic germination of orchid seeds, was introduced by Dr. Lewis Knudsen of Cornell University. It is still the most outstanding accomplishment in orchidology. Previous to Dr. Knudsen's experiments, orchid seed germination was a hit or miss affair. Seeds were scattered over osmunda in which parent plants were growing, over loam-covered bricks or on turkish toweling. Germination was indifferent; if a hundred plants were secured from several thousand seeds, that was considered a good return. Seedling growth was slow and eight or ten years might pass before plants bloomed. This old method does have the advantage of simplicity, and many amateurs today still use it. However, Dr. Knudsen's technique insures almost complete germination of fresh seeds, shortens the period between germination and transplanting. As a result, orchidists have been able to produce thousands upon thousands of new and better plants more quickly and at a more reasonable cost. Nor are they any longer dependent upon imported orchids—often poorly shipped, expensive and of limited and uncertain quality.

The technical aspects of seed germination are not beyond the scope or knowledge of amateurs. You can make the procedure difficult and costly, or simple and inexpensive if you use materials and utensils ordinarily found in homes. Actually, the procedure is more important than the equipment. The finest tools are useless if you fail to sterilize your seeds and flasks correctly, permit contamination of the agar gels. Seed-borne and air-borne fungi and algae can get into seed flasks so easily, and grow so rapidly, that they crowd out and kill orchid seedlings.

But, before you can begin the process of seed germination, you'll need to get seeds. Few orchid nurseries offer them; experienced private growers who do sell seeds occasionally are few and far apart. Sometimes botanical gardens in orchid countries will collect seeds from native orchids. The chances are, though, that most of the seeds will be nonviable because of the time lapse between gathering and planting. Generally, you'll have to produce your own seeds, and this is the most satisfactory way. You will be more pleased with the results of your own plant crosses than you would be if you had to depend on others to make them for you.

Hybridization, breeding orchids, isn't hard if you keep several simple rules in mind. Seed bearing is a strain on cultivated orchids; only the strongest plants can be used as seed parents. Furthermore, it does no good to use poor parents—nearly always the result is poor progeny. Choose plants—from the same genus, of course—that have the largest, waxiest, longest-lasting flowers, and whose color, vigor, and foliage habits you want to impart to or combine in their progeny. It is a waste of many years to grow seedlings from parent plants with which you are not satisfied.

Make your cross by placing the pollen from one flower on the stigma of the other (see Chapter 2). You can do this by inserting the narrow end of a toothpick slightly beneath the front of the column. Slowly lift it upward, pressing against the tip. The pollen wafers cling to the toothpick and can be slipped out of their receptacles. Push the pollen wafers discreetly into the cavity beneath the column. Let them rest for a moment against the sticky, stigmatic surface behind the pollen receptacle, then slowly pull the toothpick out. The pollen will adhere to the stigma. That's all there is to it. Then watch the utterly fascinating developments.

If the cross takes, and often it doesn't, in a few days the petals of most seed parents will collapse. Cypripedium flowers violate this rule; they don't collapse if the cross is successful. Cymbidium flowers, also, may not collapse, but the lip will turn brilliant red. In all orchids, though, the tip of the column will enfold the pollen, clubbing-up, and the stem—really the ovary—will swell. If you are lucky, the swelling will continue and a pod will form which when ripe splits along one of the three ridges.

If you are not lucky, and many things can happen, the entire flower may drop off within a few weeks or months. Your pollen may have been too old, too weak, or improperly cared for. Fungus may attack the seed pods, destroying the seeds. Sometimes a pod ripens, and contains nothing but worthless chaff instead of seeds. To prevent these losses, orchidists use fresh pollen and flowers; make several crosses between plants, although they use no more than one seed pod to each plant.

The time that it takes for a pod to ripen depends on the genus to which the plant belongs. Terrestrials, as a rule, ripen their pods in two to four months; epiphytes vary from six months to a year or more. For example, calanthes produce seeds in four months; laelias in nine months; cymbidiums and cattleyas require a year. The size of the pods also will differ. Small epidendrums have pods that are about a half-inch over-all; cymbidium pods may grow as big as a large apple.

During the seed-bearing period the parent plant may become ragged, the foliage and pseudobulbs shriveled; the plant uses up a great deal of stored food. Modern plant nutritionists overcome this by adding phosphorous to the plant's diet. One to three drops of concentrated phosphoric acid in a quart of water, applied to the seed parent when watering is necessary will help the plant retain its vigor. Pods don't ripen as fast in culture as they do under natural conditions in the orchid countries. The clue to quicker, better pod growth seems to be in keeping seed-bearing plants in sunnier, drier positions.

When the pod begins to split, cut it from the plant before the seeds can fall out. Snip off the end and gently scrape out the seeds. Viable seeds of cattleyas and allied genera will have yellowish and greenish centers; cypri-pedium seeds are brownish and their viability may be difficult to determine except by testing. Place good seeds in a desiccator tube and store them in your refrigerator away from the freezing coils. A tube can be prepared by placing a few crystals of anhydrous calcium chloride in the bottom of a test tube and sealing off the crystals with a cotton wad. Wrap orchid seeds in tissue paper, put them in the tube and plug the mouth with more cotton. Seeds so stored will keep for weeks at room temperature, for months under refrigeration. However, orchid seeds under the best of conditions gradually lose their viability; sow them as soon as you can. Incidentally, pollen also may be stored in desiccator tubes and kept for months in good condition.

Sowing orchid seed is simple if you follow a strict routine and complete each step before going on to the next. The technique described here is fundamentally a laboratory procedure, with the materials chemically pure and the equipment standard. That doesn't make it any harder for you. A bathroom may be substituted for a sowing box; commercial chemicals for reagent chemicals; an oven for a sterilizer; milk bottles for Erlenmeyer flasks; copper loops for platinum ones. Such substitutions are made successfully every day by amateurs. The purpose of the laboratory method is to guide you, not limit you.

Ideally, you will need a gram scale, or a druggist friend who can weigh chemicals for you. Never estimate chemical weights. Small variations in the formula can delay or stop germination, inhibit seedling growth.

A chemical supply house or drug company can sell you as little as a half pound of calcium nitrate, magnesium sulfate, potassium phosphate (monobasic), and calcium hypochlorite or one pint of commercial-strength hydrogen peroxide. Add to this a pound of powdered agar, a half pint of concentrated phosphoric acid, two ounces of brom-cresol green (0.002 per cent), six ounces of Lysol, an ounce of ferric sulphate, an ounce of manganese sulphate, and a quart of ethyl alcohol. For your convenience, and to simplify the formula, omit the iron and manganese salts, if you wish. By using commercial or fertilizer-grade chemicals (they are much cheaper) and tap water instead of distilled water, you will get as impurities all the iron and micronutrient elements orchid seedlings will need. For sugar you can raid the kitchen; only be certain you get cane sugar. For some reason beet sugar doesn't work as well in orchid culture as it does in sweetening coffee.

Lately, vitamins and auxins, amides and rare sugars have been added to orchid agar formulas with considerable success. Reports from Brazilian scientists indicate that cattleya seeds sown on agar and tomato juice grew with extraordinary vigor. As yet, however, they are not sufficiently standardized for commercial or amateur application. If you are interested in seed germination, keep in contact with university research programs. Recent experiments indicate that the correct combination of these rare and trace chemicals will cut in half the time seedlings are now kept in flasks.

These chemical supplies will make several hundred orchid flasks, but you will find twenty Erlenmeyer flasks (500 ml.) ample for your first purchase. Practice with these flasks first and then, if you want to, try milk bottles. Also order a ten-inch glass capillary tube and a two-inch piece of platinum wire, or a wide-mouthed eye dropper. Add a 100 cc. graduated liquid measure, an alcohol lamp, a nasal atomizer, a fly sprayer, several boxes of absorbent cotton and rubber bands—and your home laboratory is plentifully equipped.

While most of the chemicals and equipment can be bought for as little as $10, a sterilizer may be expensive. There is no need to buy one if you can make arrangements to use your high-school or college laboratory. Should you prefer to work at home, pick up a pressure cooker, the kind that is used for home canning of fruits and vegetables. The cooker should be large enough to hold six or seven flasks at one time. Less than this number of flasks doesn't make your time and trouble worth while. In extreme cases you can always learn to use your oven as a sterilizer.

Although a bathroom or an oven can be made temporarily aseptic and used for sowing seeds, it isn't advisable. A modified Wardian case can be so constructed as to insure aseptic conditions. Such a case need not be more than a well-made, solid crate or box about 2x2x3 feet, and covered with a pane of glass. On one side of the case cut two· armholes about four inches in diameter and about a foot apart. While you work through the armholes, the glass lets, you see what you are doing and blocks out air-borne fungus spores.

When your equipment is installed and you are ready to begin sowing seeds, weigh out the following chemicals andi dissolve them in slightly warm water:
 
FORMULA "C": DR. LEWIS KNUDSEN

Chemical                                Formula                               Weight
 
Calcium nitrate                          Ca(NOj)a · 4H2O                    1.00 g.
Potassium phosphate
(monobasic)                             KH2PO4  MgSO4                   0.25 g.
Magnesium suifate                    7H2O (NH4)2SO4                  0.25 g.
Ammonium suifate                    FeSO4 · 7H2O                        0.50 g.
Iron suifate                               MnSO4 · 4H2O                       0.025 g.
Manganese suifate                                                                    0.0075 g.
Sucrose (cane sugar)                                                                20.00 g.
Agar (powdered)                                                                      15.00 g.
Distilled water                                                                           1.00 lit.

After the chemicals have dissolved—the solution will look murky and syrupy—test for acidity. Orchid seeds will germinate and grow only if the correct acidity is maintained. Different orchid species seem to require slight variations in acidity, but most of them do well at pH 4.8 to 5.2. Above pH 5.2 germination is inhibited and chlorosis of the protocorms and seedlings sets in. Avoid guessing the pH by testing with bromcresol green, an indicator reagent. Normally, the indicator is a blue-colored solution, but at pH 5.4 it changes sharply to an orange-yellow color. Use a test plate for sampling acidity, or add one drop of the bromcresol green to the nutrient solution. If the drop remains blue as it disperses, add one drop of concentrated phosphoric acid. Make a second test; if necessary add another drop of acid. Keep this up until the indicator color changes. Usually three drops of acid are more than enough.

After you have corrected the acidity, pour 200 cc. of the solution into each Erlenmeyer flask; you have enough solution for five flasks. Stopper each flask with a husky plug of cotton pushed well down into the neck. Cover the exposed cotton with a six-inch square of paper twisted tightly against the neck of the flask and held in place with a rubber band.

Place the flasks in a sterilizer and cook them carefully. As yet, there is no good substitute for steam or heat sterilization. Chemical sterilizers placed in the flasks inhibit germination and growth, if sufficient is used to prevent fungus contamination. If ever a chemical is found that will keep the flasks sterile and not hinder germination, it will be a major advance in orchidology. Here is a wide-open field for experimentation.

Ordinarily, sterilization is accomplished with flowing steam in an Arnold Sterilizer at 100° F., one hour a day for three consecutive days. In an autoclave or pressure cooker, thirty minutes under fifteen pounds of pressure is sufficient.

Orchid flasks can be sterilized in your kitchen stove if you want to keep expenses down to a minimum. Put the flasks in the oven, close the door, bring the temperature to 225° F. and let it remain there for thirty minutes. Remove the flasks and let them cool in a clean room. Repeat the heat treatment twelve hours later. Two heat treatments may be enough, but three are better. Be careful, though, since long cooking and too high steam pressures will caramelize the sugar and make it useless for orchid seedlings.

After sterilizing cool the flasks in order to congeal the agar. If the agar doesn't gel, your original solution was made too acid. There's not much you can do except start over again. A few drops of a weak sodium hydroxide solution added to the agar will congeal it, but the hydroxide may injure seedlings.

Some orchidists leave the flasks erect, the agar solidifying on the bottom. Others tip the flasks on their sides, the necks just above horizontal and held in position by wood -collars. The latter position is considered superior since it offers less chances of contamination when sowing, provides a larger growing area for seedlings, and little or no obstruction to sunlight.

Seeds also must be sterilized—rather, they must be disinfected. The most usual method is with a solution of calcium hypochlorite. Add ten grams of the chemical to 120 cc. of water (preferably distilled). Shake well, then allow the sediment to settle. Filter off the clear solution-several layers of cheesecloth will make a good filter—and save it. Wet orchid seeds in the clear filtrate for at least fifteen minutes (never more than an hour), gently shaking the vial in order to separate seeds and thoroughly disinfect them. Bromine water, diluted one to ten, and 8-hydroxy-quinoline-sulfate are good disinfectants; chlorazene, one tablet (4.6 grains) in an ounce of water, is another. The latest technique, and one rapidly increasing in popularity, is to soak orchid seeds for twenty minutes in commercial strength (6 per cent) hydrogen peroxide.

Orchid seeds are hard to wet. They may float, shed water from their surfaces, or drop to the bottom of the disinfecting solution in a tight mass. While agitation helps, a drop of a well-diluted wetting agent will work wonders in dispersing seeds through the solution. Put one drop of Aerosol in 25 cc. of water; add one drop—and only one drop—of this dilution to the disinfecting solution.

Bathrooms may be sterilized by letting hot water run in the shower or tub until the room is filled with steam. As the vapor condenses it picks up air-borne spores and deposits them on walls and floor. Spraying with Lysol is additional insurance against contamination. Also spray your flasks and equipment and lightly, quite lightly, your arms and hands. Better still, rub your hands and arms with alcohol. Hands and fingernails are a continuous source of contamination.

Ovens, too, may be used for sowing seeds. Set the temperature at 225° F., heat for one hour and then cool. When the oven is barely warm, open the door, insert your flasks and tools (previously sprayed with Lysol), and go to work. Three or four flasks are all you can sow in an oven at one time since air contamination reoccurs rapidly.
There is little question that a sowing box is the most convenient and safest way to sow orchid seeds. It only needs to be sprayed with Lysol after you have added your flasks and equipment. It will stay aseptic a long time regardless of the room in which it may be placed; and can be resterilized easily and conveniently.

 

SEED SOWING AND GERMINATION

Top: Germinating Flasks and Storage Racks; Sowing Case

Bottom: Sowing with Platinum Loop; Sowing with Eyedropper

There are several methods of sowing seeds and each one has its devotees. About the best one, at least for beginners, is to pick up orchid seeds from a 3 per cent hydrogen peroxide bath with a wide-mouthed eye dropper. Seeds are simply squirted into the flasks. Of course, the eye dropper must be disinfected by boiling in water for at least twenty minutes before you use it. Another simple method is to dump seeds from a small vial into flasks. Barely cover the seeds with a chlorzene solution (about 1 cc), swirl the vial to distribute the seeds evenly, and pour them out. Naturally, with these two methods the flasks, originally, must be cooled in a vertical position.

The most usual procedure is to use a platinum loop with either calcium hypochlorite or commercial hydrogen peroxide. Both disinfectants are rough on seedlings, and very little of the solution should be allowed to reach the agar. Make a loop by twisting the platinum wire in a circle about one-fourth inch in diameter. Leave one end of the wire overhanging and insert the end into the glass capillary tube. Heat the end of the tube until the glass softens and binds the wire. The platinum loop can be soldered to a ten-inch, fourteen-gauge copper or steel wire, but the chances of contamination are greater. Before using the loop, sterilize it by dipping into alcohol. Afterward, as necessary, pass it through the flame of your alcohol lamp.

There are two ways of using the loop. The first and safest method, though more troublesome, is to dip the loop into the disinfectant and pull it out. A thin film of the solution will cling to the loop and often carry with it enough seeds to plant one flask. The second method is to drain the seed on sterilized absorbent paper in order to remove as much of the disinfecting solution as possible. Of course the seeds must be kept free from further contamination when the disinfectant is removed. You can only do this with reasonable safety in a sowing box. After draining, but before the seeds are dry, pick up enough seeds with the platinum loop to plant one flask. In most cases enough seeds to equal half the size of a grain of rice is adequate for a single flask. This amount of seeds will give you approximately 1,000 seedlings.

After sowing your seeds, recap the flask. Never leave flasks open too long; in fact, never open more than one flask at a time. Singe the cotton plug in the flame of the alcohol lamp, or spray lightly and thoroughly with Lysol or a strong solution of copper sulphate. A nasal atomizer comes in handy for spraying cotton plugs. Either flaming or spraying resterilizes the plug and is a further protection against contamination. You can smother the flame with your hand or with the original paper square. Then refasten the paper square to the flask with a rubber band, and you are through.
 
When you use a loop it is difficult to get even distribution of the seeds over the agar. They are inserted in a clump and stay that way. Smearing them about with the loop is frequently damaging to the seeds; they are torn or buried in the agar. In either case they don't germinate. If you sow seeds soon after the agar cools, a thin film of moisture generally covers the agar. By gently swirling and rocking the flask, the seeds may be separated and moved over the agar in a thin layer. In case there isn't any covering of moisture, add four or five drops of distilled water and then swirl the flasks. Unless correctly done, adding water is one of the easiest ways of contaminating flasks. Distilled water must be boiled first. Both the container and the spoon must be sterile. Sometimes it is better to use a sterile eye dropper instead of a teaspoon, and keep the water in a sterile dropper bottle. Use of tap water is inadvisable, unless acidified (and sterilized), since it will decrease the acidity of the nutrient agar. One or two drops of phosphoric acid in a quart of tap water is enough to keep the pH from changing in the flasks. Be sure you boil the water furiously. Boiling the eye dropper and bottle at the same time and in the same water is a timesaving trick.

After you have sown your first batch of orchid flasks, and it is a thrill you will never forget and often talk about, your real trouble and fun begin. You have to germinate the seeds, grow the seedlings, and finally transplant them to regular pots. Mostly this is just a job of providing the correct conditions and waiting for the seeds to do the work. If you haven't a greenhouse, store the flasks in a Wardian case. The latter is better anyway since it gives you accurate control of temperature, humidity, and light.

Keep the flasks at a temperature of not less than 68° F.; not more, if you can, than 86° F. Adjust the humidity to 70 or 80 per cent during the daytime, considerably less at night. These wide variations in temperature and humidity cause an air exchange inside the flasks, keeping the air fresh. During germination the flasks should receive filtered light (about 35 or 40 per cent of the normal seasonal light). Cheesecloth, Bon Ami or whitewash on the glass are excellent filtering materials. As the seedlings develop, gradually lower the temperature and humidity and increase the amount of light. The danger, in growing seedlings, lies in the extremes of temperature and too little or too much light. Low temperatures rot seedlings; high temperatures and too little light weaken them; too much light causes chlorosis (blanching of the green parts). Watch youi seedlings closely, and adjust conditions to meet their growth requirements.

Germination of most orchid seeds occurs within four to six weeks. The seeds swell, become fat globules (yellowish green for cattleyas and allied genera, brown for cypri-pediums), and then break out in sharp points which later divide to become leaves. Just what happens inside the globules to stimulate and produce from undifferentiated protoplasm the stems and leaves is one of the miracles of the plant world—and one of the puzzles of orchidology. After the third leaf appears, most seedlings are ready for transplanting. This period of growth may take three months or it may take thirteen; again the slowness or rapidity with which seedlings develop depends on the genus to which they belong.

Many of the seedlings will have roots; some will not, but that is no deterrent to transplanting. Those that have no definite roots will be covered with microscopic or barely visible root hairs. Don't throw these latter seedlings away. Separate them from those that do have roots, transplant them in the same manner, but provide them with higher humidity, more equable temperatures, a bit more shade, and frequent top spraying with a syringe of water. In a short time, those that live will produce their own roots and can be placed with the more advanced seedlings.

There is no trick to lifting seedlings out of their flasks. Spoon them out with an iced-tea spoon or cut them out of the agar with a dull knife, flat stick, or a curved piece of wire. Merely be careful not to injure the roots or foliage. Wash off the agar in mildly warm water, drain the seedlings on paper toweling, and plant them in community pots. These are ordinary red clay pots ranging in diameter from two and one-half to four inches. Fill the pots half full with small rocks or crocks for drainage, then add finely chopped osmunda until it is tightly packed between the walls of the pots. Transplant seedlings, ten or twenty to a pot, by pushing a small hole into the osmunda with a pointed stick, inserting an orchid and firming the osmunda back in place. It is as simple as that. Among the more experienced orchidists terrestrial seedlings are planted in various mixtures of loam, leafmold, and gravel. Unless well cared for they are liable to damp-off; osmunda is a safer medium for all seedlings.

It is not always so simple, though, to carry seedlings on after transplanting. They are easy prey for pests and die rapidly if growing conditions are unsuitable. Be sure to spray them overhead several times a day when there is enough sunlight and warmth. Never permit the osmunda to stay too wet or too dry for long periods. Keep the daytime humidity fairly high and provide shade as necessary. Young seedlings are very tender until they develop good, leathery leaves or sturdy pseudobulbs. Before this stage a Wardian case is a good place in which to grow them; afterward you can treat them pretty much as you would adult plants.

The time for the second transplanting varies as widely as do the genera of orchids, and sometimes within the species also. The only reliable rule is to transplant from the community pots just before there is any danger of overcrowding. This is most likely to occur somewhere between the sixth and tenth months from the time of the first transplanting. Then transplant to thumb pots (the two-inch size is excellent), and grow the seedlings on with your regular plants. Never replant after that until each seedling almost fills its pot or the osmunda requires changing. Increase the pot size about a half inch at a time.

Are You Ready To Move Onto The Next Lesson? Click Here...