PARK ADMINISTRATION, JULY, 1952. pp. 94 - 96


By G. van Son. D.Sc.. F.R.E.S.
(See also article on page
63, April. 1952. — Ed.}

Cultivation of plants has always been one of my hobbies. By the time I was nine years old, I was shown by our head-gardener how to graft roses and fruit trees. But these gardening activities had to be interrupted for many years with my entering a cadet school and later the Marine Corps in St. Petersburg. The Russian revolution of 1917 caught up with me while I was on a cruise in the Far East, and with the loss of everything that followed, I managed, in 1921, to find asylum in my late father's country, Holland, from where I came to South Africa in 1923. Being engaged in entomological work, and working for my academic degrees, I was prevented from doing much gardening at that time.
However, I became interested in orchids during a brief visit overseas in 1934, and brought back with me a few dozen plants received in exchange for seeds of succulents. Having soon realised that "green fingers" alone are not quite enough where orchids are concerned, I endeavoured to obtain some books dealing with the cultivation of orchids. Through my late friend, Mr. F. Postma, of Pretoria, I managed to acquire Constantin's Atlas des Orchidées cultivées. With the aid of that book, I made my first pollinations of Cypripediums in 1940, and a year later got my first thrill when I saw the first tiny seedlings appear in flasks with sterilized sphagnum-moss, inoculated with pieces of Cypripedium roots harbouring the fungus without which no orchids can germinate under natural conditions. This encouraged me, and when one of my Cattleyas produced two very nice and large blooms, I decided to try my luck with them. Mr. Postma let me have the pollinia of two of his best Cattleyas, and in a short while I had two fine pods set on my plant. Fourteen months later the pods started to burst, and I had enough seed to fill all the glass-houses in the world ... if I only could germinate them.
I tried the old Cypripedium method, and managed to get about one in a hundred seeds to germinate, which I thought was not good enough for me ! So without further delay, I decided to try out the so-called asymbiotic method (that is, the method in which the symbiotic fungus is omitted), the formula for which I got from Constantin's book. The snag of this method lies in the necessity to handle things aseptically, that is, without letting into the sterilized flasks a single spore of a fungus, or a single bacteria, otherwise the whole culture will be lost in the end. After several unsuccessful attempts, I finally succeeded to reduce the number of contaminated flasks to about one or two out of ten. This was, of course, quite sufficient to raise far greater quantities of seedlings than I could possibly attend to. However, when a year or so later the time came to open the flasks and start pricking out the contents, I soon found out that a large number of seedlings were inevitably lost to various enemies, damp-off, slugs, snails, cockroaches, etc. Ways and means had to be devised to protect the little plants. When these were large enough to be potted up singly, I found that, in the absence at the time of thumb pots, short sections of old reeds served the purpose very well, and being light, allowed one to group about 50 or more together in a tomato-box, suspended from wires stretched across the glass-house. The latter was erected as soon as it became obvious that the little conservatory would be hopelessly inadequate to house even a small portion of the raised seedlings.
The potting medium used by me at the time was chopped-up osmunda-fibre, as recommended by most books, which was "gingered-up" by some old fibre taken from well-growing plants, in order to introduce the beneficial root-fungus. Since it became obvious that we can grow orchids from seeds as well as anybody else overseas, I offered the Superintendent of the Port Elizabeth Parks to raise, or try to raise, any orchid seed they would be willing to produce. The efforts of Mr. F. J. Cook and Mr. Burbridge were rewarded by a good measure of success, as the article in the April number of Park Administration has shown. I think it is right to mention here that it was largely due to the foresight and initiative of our Editor, Mr. F. R. Long, that these achievements were made possible.
Now that the tale is told, there remains a little to be said concerning more recent advances in orchid culture.
Firstly, the formula used in the germination of seeds is not a secret at all, in fact there exist several formulas which can be successfully used. The main ingredients are as follows ;—
  Calcium Nitrate .... .... .... .... .... 1 gr.
  Potassium Monophosphate .... .. 0.25 gr.
  Magnesium Sulphate .... .... .... . 0.25 gr.
  Ammonium Sulphate .... .... .... . 0.5 gr.
  Ferric Sulphate .... .... .... .... .... 0.05 gr.
  Manganese Sulphate .... .... .... . 0.0075 gr.
  Sugar (Glucose or Sucrose) .... 20 gr.
  Agar-agar .... .... .... .... .... .... . 14 gr.
  Distilled water .... .... .... .... .... 1,000 cc.
Besides, it is necessary to adjust the acidity of this medium to a degree which suits the various types of orchids. This degree, or pH, as it is called, must be around 5 for Cattleyas, but for Vandas it must be closer to 6, and for Angraecum about 4.5 ; Cymbidiums like about 4.7. The main difficulty in this type of work is to ensure absolute sterility of both seeds and the medium. To sterilize the seeds, I dip them in a solution of Chloride of Lime (about 12 gr. to 150 cc. of water), which has been carefully decanted to eliminate the powdery residue; the dipping not to exceed 5 to 7 minutes, as longer dipping may kill the seeds.
The flasks, after having been filled to about an inch from the bottom with the previously heated and completely liquid medium, are stoppered with tight wads of cotton-wool and either sterilized for about 20 minutes in a pressure-cooker, or steamed above boiling water in a big pot covered with a lid, three times for about half an hour each, at intervals of 24 hours.
The most difficult part of the sowing is the placing of a little lump of sterilized seeds into the flask, using a long-handled platinum needle, previously and immediately before its use heated in a spirit flame and cooled in spirits. Both the taken-off stopper of the flask and the needle have to be held in the right hand, while the flask is held in an inclined (downwards) position with the left. As soon as the seed is dipped into the little water, which always accumulates in the flask above the medium, the needle is withdrawn and the stopper replaced, after which the flask is laid on its side, and the next flask is tackled in the same way. After the flasks have been sown, they are singed well around the neck in a spirit flame, still in a horizontal position, and only after this are stood upright ; this procedure kills any spore or bacteria which might have got into the neck during the sowing. The seeds take about two weeks to germinate.
Now something about potting media. I have found, after about 15 years' experimenting, that the classical medium used overseas, that is, a mixture of osmunda and sphagnum, or even pure osmunda, is on the whole not to be trusted in this country, unless one has only a few plants to deal with, because the frequent sprayings necessitated by our dry climate tend to overwater and rot the osmunda very quickly, followed by inevitable loss of roots while keeping the plants on the dry side makes the same medium practically impervious to water, especially in the case of small pots which may completely dry out in a single day. Therefore, I have almost completely gone over to the so-called "gravel-culture", which consists in potting the plants in clean gravel, preferably granite or quartz (not alkaline), varying in size from ½ inch to ¼ inch, and even much smaller for seedlings. It is a well-known fact that the absorbing part of orchid roots is invariably attached to the pot and therefore receives only a very small part of the nutrient elements contained in the whole pot of, say, osmunda and the remaining big part of the compost simply rots for nothing and is only harmful to the roots. Since I have been using this gravel method, my plants have improved beyond belief, and damping-off of seedlings is a thing of the past. Naturally, a plant cannot grow on fresh air alone, and therefore the plants are watered occasionally (at most once a week, preferably once in two weeks), with a nutrient solution. This consists simply of a level teaspoon of "Hyponex" to every two gallons of water. There is no harm in topping the pot very thinly with osmunda or some clean tanning-bark ; this keeps up the necessary acidity, but can be completely dispensed with if the pH of the water is tested now and then and adjusted to a little below 6.
The great advantage of the gravel culture lies in the extreme ease of transplanting, without any damage to roots, and also in the much better aeration of the root system, practically eliminating the danger of over-watering. If we consider the natural growth of epiphytic orchids, with most of their roots exposed to air and not rammed in a tight compost, we must admit that the gravel culture is more natural than the tight osmunda-sphagnum potting practised overseas and requiring re-potting every second year, without which the plants invariably deteriorate. With gravel culture, re-potting only becomes necessary when the plant outgrows its pot, which takes several years, as much larger pots can be safely used than would be possible with the old method.
In large establishments, coupled with shortage of skilled labour, the gravel culture is a "must".
Finally, may I wish "Good Growing" to all would-be orchid growers among members of the Institute.

Dr. G. van Son holding one of his many outstanding hybrids.