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PALM BARK AS A POTTING MEDIUM FOR ORCHIDS

 

by

Wilella Stimmell

 

(Printed in "The Arizona Orchidist", June, 1991)

  

First let's briefly review what we know about root growth of epiphytes.

 

Most cattleya alliance species grow as epiphytes in nature. As their Greek name implies, epiphytes grow above ground on other plants, not as parasites draining nutrients from their hosts, but as botanical hitchhikers borrowing tree branches for a place in the sun. Having obtained a position in the canopy of a rain forest, epiphytes must struggle to obtain food and drink. The part of the forest which epiphytes colonize presents conditions which are often harsh. Though much rain may fall, there is no soil on branches from which roots may absorb it. There is also little chance to extract nutrients released through decaying detritus that falls to the forest floor. High in the canopy, epiphytes exist in an almost perpetual famine, in constant danger either of drying out or of drowning. Consequently, many of the epiphytes here have similar characteristics to those found in deserts, despite growing in the wettest regions of the world. To survive, they have evolved a range of adaptations which are some of the most remarkable in the plant kingdom.

 

Some epiphytes are capable of shutting down their metabolism in times of drought until the next deluge, when they miraculously return to life and begin to bloom. Many have leaves toughened with waxy coatings to cut down water loss. Some orchids have gone one step further - reducing their leaves and roots to small strands in order to cut down the surface from which water can evaporate.

 

Almost half of all the nutrients in the rain forest canopy foliage may be pirated out of the air and locked up by epiphytes. (See note 1)

 

To successfully grow epiphytes, we must attempt to duplicate their native habitat. We need to select an anchor (the potting medium) for the roots.

 

Most desert orchidists use fir bark as the favored medium for epiphytes, but fir bark did not become popular or readily available until the 1950's. Dr. Thomas J. Sheehan, whose name we recognize as the author of most responses in the "Question Box" in the AOS BULLETIN, wrote in the PROCEEDINGS OF THE SECOND WORLD ORCHID CONFERENCE (Honolulu, 1957), in the text of his lecture on orchid potting media, that "the use of bark is most likely due to the growth response of plants in the media, ease of potting, low cost, and long life." (See note 2)

 

These are still valid reasons for choosing fir bark, but as it becomes more difficult to obtain and the quality of the product continues to decline, we must look elsewhere for a suitable potting medium.

 

Some of our native desert plants may furnish our potting medium needs. The skeleton of cholla cactus, so abundant in our desert, is a poor choice. Though the chemical composition of the live cholla has almost certainly degraded, orchid roots are nevertheless "repulsed" by proximity to cholla "wood". Cottonwood, also abundant, is another useless selection and for the same reason. WHAT you try is limited only by the time you devote to experimentation.

 

Enter member Deacon Bell at our April meeting with a sack of palm bark in one hand and a vigorous cattleya hybrid in bloom in the palm bark in the other hand. (Deacon celebrated Earth

Day long before it was fashionable to recycle things. And true to form, he had not discarded his palm tree trimmings.)

 

There are at least a dozen species of palm trees in this area, and theoretically, the chemical and botanical composition of each should be similar. The most prevalent palm in our area, however, is the Washingtonia, native to the Sonoran desert.

 

Should you decide that palm bark is the answer to your prayers, DO NOT sweep through your orchid collection and repot every plant in sight. Experiment! Try potting 1 or 2 plants, and vary the fertilizing methods so you have comparison results. (Deacon's results were obtained by feeding the plant the same type and quantity of fertilizer as he feeds his other cattleyas.)

 

Treat the palm bark as an organic medium which supplies some nutrients to the plant's roots. This implies a more dilute feeding than if you were using an inorganic medium, such as cinders.

 

Palm bark is easy to use (when moistened and then chopped into pieces) and the price is outstanding (if you've got palm trees in your yard...or know a friend who does, the medium is FREE!) Only time will tell whether plants potted in palm bark, assuming the pot is large enough to accommodate several new growths, will continue to thrive undisturbed for many years.

 

 

Note 1. Mitchell, Andrew. THE ENCHANTED CANOPY: SECRETS FROM THE RAINFOREST ROOF. Glasgow, Scotland: William Collins & Co., Ltd., 1986. (Mitchell is a pioneer in the use of lightweight aerial walkways for exploring the rain forest roof.)

 

Note 2. PROCEEDINGS OF THE SECOND WORLD ORCHID CONFERENCE. Cambridge, Mass.: Harvard University Printing Office, 1958, "Orchid Potting Media", pp. 226- 230.

 

 

Five Years Later: Palm bark as a potting medium proved to have more disadvantages than advantages. It degraded in less than a year and turned to mush, and snow mold fluorished. Although there was no root dieback, a more frequent need to repot was definitely not anticipated...nor the extra work appreciated!

 

FIR BARK VS. PINE BARK

 In the "Question Box" of the April, 1991 issue of the AOS BULLETIN, Dr. Thomas J. Sheehan, University of Florida, states: "I am a firm believer that epiphytic orchids can be grown in any medium except soil as long as adjustments are made to watering and fertilizer practices used with the medium." In his response to an orchidist's inquiry about the suitability of pine bark, Dr. Sheehan suggested the grower try growing a few plants in it.

 

A review of the literature on various potting media revealed an opposing view regarding pine bark. In an article "Bark Culture from A to Z", AOS BULLETIN, Sept., 1958, Dr. L.F.Hawkinson stated: "Botanically and chemically, there is a marked difference between pine bark and fir bark. Pine bark contains considerable resin which seems to be detrimental to growth." Corroboration of the undesirability of pine bark was indirectly given by Dr. Harold E. Anthony, staff member of the American Museum of Natural History for nearly 50 years and participant in field expeditions. He observed how orchids grew in their natural state on four continents. In discussing a collecting trip to Mexico, he stated: "We walked for several miles through continuous pine forest without observing orchids and only when we came to a semi- open spot with oaks scattered among the pines did we see orchids in abundance. Here the favorable factors probably included light and rough oak bark." (The full text of Dr. Anthony's remarks may be found in SECOND WOC PROCEEDINGS. Ibid. "Common Sense in Orchid Growing", pp. 215-221.)

 

 

Culture Tip from the Archives

 

Dr. R.E.Holttum, author of ORCHIDS OF MALAYA, Singapore, 1953, had an unusual (and a touch disgusting) preference of fertilizers.

 

"In my experience, by far the best manure for orchids is dilute urine (diluted at least 1:10 with water). This contains all the necessary salts, and also certain growth-promoting substances, which doubtless have some effect..."

 

The above quotation was taken from the "Cultural Column", THE ORCHID JOURNAL, December, 1953. This short-lived publication was edited by Alex D. Hawkes.

 

 

 

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