FERTILIZERS IN ORCHID CULTURE

by

Wilella Stimmell

(Reprinted from "The Arizona Orchidist", Dec., 1995)

"Which is the best fertilizer to use on orchids?" This is a question often asked not only by novice growers, but by experienced growers who feel their plants aren't growing or blooming satisfactorily. We keep searching for a better fertilizer than the one we're using. If a poll were conducted amongst any number of experienced growers, you might be surprised at the number of "bests" for use on orchids. We have heard commercial growers at our meetings recommend one product on the market and pan another. Another grower may prefer a product we were told was unacceptable. We heard one speaker tell us that "fertilizer is a racket". Most citizens living in a democracy understand about diversity in the marketplace, but such awareness is not helpful when we need guidance in choosing one product over another.

Whether to fertilize orchids and if so, how to determine the mixture and amount that will produce the best plant growth and orchid blooms, has been a matter of considerable controversy. A review of the literature on the subject revealed that before 1946, the consensus was that it was unnecessary and possibly harmful to fertilize most epiphytic orchids. Many growers had been using osmunda fiber as a growing medium, without fertilizer, and were pleased with the results. However, hobbyists found osmunda difficult to handle. And, as with any natural resource, the superior-grade supply was depleted first. Osmunda is still available, and some veteran growers still use it, but they lament the situation that "you can't buy good quality osmunda anywhere". The need to fertilize orchids became more important when growers began to experiment with inert materials as growing media.

In 1946 the first fertilizer experiments with orchids were begun by O. Wesley Davidson at Rutgers University. Nutrient solutions were diluted to only 10 parts per million of nitrogen. As results were obtained, the proportion of nutrients was varied. The name Dr. O. Wesley Davidson, distinguished authority on orchid culture and pioneer developer of liquid nutrients, is well known to readers of back issues of the AOS BULLETIN. For many years, Dr. Davidson was the Editor of the "Question Box", and he wrote definitive articles on the subject of orchid ailments. Every conscientious orchid grower should read these articles.

Almost fifty years ago it was known that orchids were relatively slow-growing plants, that their nutrient requirements were low, but that flower quality and plant growth were enhanced with small amounts of a nutrient solution - even for plants grown in osmunda, which has a higher nitrogen content than fir bark.

Through the years, many orchid culture experts have tended to agree that a dilute, balanced fertilizer should be used, unless the plants are potted in fir bark. (Bark supposedly needs more nitrogen because the fungus that causes the bark to decompose, robs the plant of nitrogen. However, there are successful, commercial growers whose orchids potted in bark, are fertilized with a balanced fertilizer.) A balanced fertilizer contains equal parts of nitrogen (N), phosphorus (P), and potassium (K). There are other macroelement-minerals needed by the plants, but these three are the ones identified by numbers on fertilizer labels. For example, if the label on brand X lists 30-10-10, the first number is the nitrogen content, the second is the phosphorus, and the third is the potassium. There is a second group of minerals known as microelements needed by plants. These minerals are also known as trace elements because very small amounts are needed. Not all fertilizers contain trace elements. The most research on orchid nutrition has involved cattleyas, phalaenopsis, and cymbidiums. Therefore, it is not surprising that the many fertilizers on the market were formulated to satisfy the nutritional needs of these genera, depending on the medium in which they were grown.

The controversy continues over the form of nitrogen that orchids should receive. In the fine print of a fertilizer label, the nitrogen content is listed as urea nitrogen, ammoniacal nitrogen, or nitrate nitrogen. Most products use two forms of nitrogen, with one form a higher concentration than the other. Generally, a product with a higher nitrate nitrogen and a lower ammoniacal nitrogen is recommended. However, there are successful commercial orchid growers and hobbyists who pay no attention to the form of nitrogen. In my research for this article, I interviewed a few commercial growers for whom I have great respect. In answer to my question, "Which form of nitrogen do you use on your orchids?", one grower surprised me by his silence. Figuring he had not dropped dead, I further inquired, "Nitrate, ammoniacal, or urea?" Finally he responded, "That's too scientific for me. I just use 20-20-20." He grows his orchids in fir bark.

In an excellent article, "Confessions of an Overwaterer", written by judywhite and printed in the AOS BULLETIN In May, 1990 (Volume 59, Number 5), pp. 483-494, the deleterious effects of urea nitrogen are discussed.

In ASEAN countries, chicken manure (5-3-1.5) is still used to fertilize orchids, but the use of chemical fertilizers is gaining ground. I probably do not need to mention that the orchids receiving chicken manure, are grown outside! (The six active member-nations of the Association of Southeast Asian Nations are Brunei, Indonesia, Malaysia, Philippines, Singapore, and Thailand.)

Fertilizing is but one element of orchid culture. Read all you can about various products on the market, talk to experienced growers, then take a deep breath and pick a product. Your experiences with the product will dictate whether you need to keep searching for a "better" fertilizer. Begin with a simplified process: a quarter- strength dilution of fertilizer every time you water. Do NOT fertilize orchids that are NOT in active growth. Flush the pots with plain water every month. I have not mentioned "blossom booster-fertilizers" (formulations where the nitrogen number is lowest, the phosphorus number is highest, with the potassium number between the highest and the lowest) because you will discover these formulations when you begin to study fertilizer labels.

Bibliography:

Arditti, Joseph. FUNDAMENTALS OF ORCHID BIOLOGY. New York: John

Wiley & Sons, 1992, pp. 196-206.

Arditti, Joseph. (Ed.) ORCHID BIOLOGY: REVIEWS AND PERSPECTIVES, VI. New York: John Wiley & Sons, 1994, pp. 381-384.

Davidson, Dr. O. Wesley. "It Pays to Fertilize Orchids". AOS BULLETIN, Volume 21, Number 10, October, 1952, p. 743.

Davidson, Dr. O. Wesley. "Orchid Ailments not Caused by Insects or Diseases". AOS BULLETIN, Volume 36, Number 6, June, 1967, pp. 472- 475.

judywhite. "Confessions of an Overwaterer". AOS BULLETIN, Volume 59, Number 5, May, 1990, pp. 489-494.

Northen, Rebecca. HOME ORCHID GROWING. (Fourth Revised Ed.) New York: Prentice Hall, 1990, pp. 33-38.

PROCEEDINGS OF THE FIFTH ASEAN ORCHID CONGRESS SEMINAR. Singapore: National University of Singapore, 1986, pp. 51-54.

Scully, Robert M. "Should Orchids be Fertilized?" AOS BULLETIN, Volume 20, Number 3, March, 1951, pp. 137-139.

THE NEW YORK BOTANICAL GARDEN ILLUSTRATED ENCYCLOPEDIA OF HORTICULTURE. Thomas H. Everett, Editor. Vol. 7. New York: Garland Publishing, Inc., 1981, pp. 2422, 2423.