header


VEGETABLE SUBSTRATES
FOR THE ORCHIDS
EPIPHYTIC CULTIVATION.

by Maria Esmeralda Soares Payão Damatté



Text extract from the Associate Professorship thesis of Prof. Esmeralda Payão Dematée, of the Horticultural Department of the Faculdade de Ciências Agrárias de Jaboticabal, Federal University of São Paulo (UNESP) (1992)



In Brazil, the tree fern fiber has been explored in prejudice of the Serra do Mar flora, it is extracted in big amount, from the species that, besides not to be replanted in a big extent, grow very slowly.

The true tree fern, Dicksonia sellowiana (Presl.) Hook, is already rare so, nowadays the extraction is made from Cyathea shanschin Mart. Since 1990, the Brazilian laws limit the tree fern cut but, although it is doing inside the established limits, the product remains still intensively commercialized in inside Brazil and international market.

On the other hand, the orchids cultivation is important for two raisons, first because the species, in the wild, are threatened by extinction due to the destruction of their habitats and, secondly, because the commercial interest involving the sale.
As a result, the studies concerning the materials that can substitute the tree fern fiber as a substrate must be done, contributing for protecting, at the same time, the species which supply it and the Orchidaceae species.

Without a firm and well ventilated substrate which provides the settlement, the growth and the activities of the roots, orchids can't absorb water and nutrients needed. Although there are many adequate material, the choice is restrained by the availability in reasonable price and by the facility in obtaining it. The basic qualities of a good substrate must be: availability, good price, easy to deal with, able to maintain the plant firmly, longevity (it should last from 4 to 6 years), firmness, lack of toxicity and good ventilation.

The tree fern fiber presents all those qualities besides to be rich in nutrients and is considered, until now, as the ideal substrate for epiphytic orchids.

In the Northeast of Brazil, the coconut bark (Cocos nucifera L) has been used in orchid cultivation since the last century and the coxim, made from this bark, is a semi-industrialized pressed product forming small cubes, logs and slabs. It is a material which seems to be promising and can become an important product for the Northeast economy having as raw material-prima the industrial residues from the factories of coconuts fibers. The aggregation of this residue was obtained by Augusto Ferreira. With this aggregation, the inconveniences of the natural coconut bark have been eliminated and he has obtained a material without addictive, strongly hydrophilic which can become the tree fern fiber substitute. Having long lasting durability, it provides a good growth and good blooming, also supplies nutrients to the plants exempting the fertilization. According to the producer, it doesn't alkalize when decomposed and stabilize its pH at about 5,2 to 5,3, presenting a medium pH at about 5,53.

This study has been done during 36 months, having Dendrobium nobile Lindl as a test-plant. The experiences have been realized in 50% shade plant houses made of laths, in Jaboticabal, São Paulo.

The purposes were:

- Characterize the materials of vegetal origins used as substrate for epiphytic orchids concerning the physical properties (color, texture, density, water lost and structures alterations in relation to time) and chemical (pH and nutrients concentration) ;

- Comparing Dendrobium nobile development in different studied substrates having the tree fern fiber as witness.

- Recommend the adequate material to replace the tree fern fiber.

The following substrates have been utilized:

1- Tree fern fiber (as witness);

2- Coxim;

3- Eucalyptus grandis bark;

4- Coxim (50%) mixed with Eucalyptus grandis bark(50%);

5- Coxim (70%) mixed with charcoal (30%)

6- Eucalyptus grandis bark (70%) mixed with charcoal (30%)

7- Coxim (38%) mixed with Eucalyptus grandis bark (35%) and charcoal (30%)

The containers with the studied substrates have been maintained in the same environment conditions and periodically many tests have been executed in order to do different verifications: Water lost and alteration in original structure in relation to time, pH, the concentration of macro and micro-nutrients, among others. Among the studied material, the coxim bears most resemblance to tree fern fibers and this likeness is interesting to the point of commercial view because of the esthetic effect with which the customer is used to. Regarding to the global density which reflexes on the pot weight, no substrate is more advantageous than tree fern fiber while the coxim weight is a problem to hang pots and to transport them. On the other hand, the weight of small cubs helps to fix the plant in the pot and replant becomes easier and faster.

The results obtained with the coxim confirmed that, at the first, there is no too much water retention but with the use, the material acquires the capacity of retaining humid. Coxim was the substrate which remains for more time inside the suitable levels of pH, between 4,8 and 5,5, considered as ideal for orchids cultivation. In the mixture of coxim and charcoal, the pH level remains suitable for a more restrict period. The pH of the other substrates weren't inside those suitable levels. Concerning the nutrients, when new, the coxim distinguished itself, overcoming the new tree fern fiber in the concentration of phosphorus, calcium, magnesium, boron, magnesium, molybdenum and mainly, potassium, The most big problem presented by the Eucalyptus bark was the alteration of its structure and after a certain time of using, it becomes an inadequate substrate for the orchids cultivation because of lost of porosity which is indispensable for the good aeration. In this aspect, the advantages of coxim and charcoal were showed clearly.

The charcoal, although considered as a inert material, presented significant concentration of nutrients except for phosphorus. From this study, it has been concluded that crushed Eucalyptus grandis bark, without mixture, is not appropriated as a substrate for epiphytic orchids. Among the substrates studied, the coxim without mixture is the one which assemble more advantages for substituting the tree fern fibers.

It presented the following advantages regarding to the other proposed substrates.

- It looks like tree fern fiber;

- It is easy to deal with;

- The aeration and drainage are good;

- Big capacity of retaining humidity after being used for some time;

- Durability;

- pH suitable;

- Adequate nutrients compositions after a period of leaching

On the other hand, it presented the following disadvantages:

- It presented a big density which arises the transport costs and makes the pots very heavy.

- It retained little humidity when new making necessary to let it immerses for a period before its utilization (the coxim has already suffered some modification for increasing its capacity to retain water).

- It presented a high initial level of nutrients which can disadvantageous for the orchid.

- It is still an expensive material and the availability is restraint.

The cost is a factor of big importance that should be considered to choose the substrate.

The coxim, in the south of Brazil, is more expensive because of the transport since it is made in Recife and need to be ordered to the producer but this is a situation which is modified as time goes by.

Eucalyptus bark can be free obtained. In order to reduce costs, the coxim can be mixed to charcoal, crushed Eucalyptus grandis bark or both materials although those mixtures were inferior when compared with the other advantages above. Eucalyptus bark can be got free and the charcoal is sold a cheap price. But we must say that it is made, very often, from the cut of the trees which occur en native woods, provoking its devastation.

On the other hand, the tree fern fibers price, which substitution is proposed, increased in the proportion the material become rare.

It is necessary to do previous tests with the species to be cultivated although the results obtained with Dendrobium nobile have been satisfactory.




line/linha





clique aqui/click hereBack to Orchid NewsStay at the Forum clique aqui/click here