Sunday, March 05, 2006

Why Must We Fertilize Orchids



Why Must We Fertilize Orchids



Written by [Philippine Orchid Review] Rudy and Soly Pagcatipunan
Sunday, 01 August 2004
Plants, orchids in particular, can live with just regular watering, but many do not grow vigorously or flower which we , as orchid lovers, desire so much.
Orchids through photosynthesis, can manufacture their own food for energy. Water (H2O) is absorbed through the roots and diverted to the leaves by capillary action. Underneath the leaves, are tiny opening called stomata, where carbon dioxide (CO2 ) gas can enter. With the aid of sunlight and the green coloring pigments called chlorophyll, carbon is fixed. H2O and CO2 will combine to produce sugar (C2H12O6-glucose ) and oxygen (O). Actually they do not produce simple sugar ( glucose ) but a more compound sugar, like hexose monophosphate, but for our purpose we just mention sugar. This sugar will be use by the orchid for its growth or maintenance of body parts.
Sunlight
Chloriphyll
6CO2
+
6H2O
---------->
6O2
+
C2H12O6
From Air

From Roots

Oxygen

Sugar
Photosynthetic Activity in Orchid Leaves
Water, whether from municipal or deep well, contain not only hydrogen (H) and oxygen (O). They contain several elements such as calcium, magnesium, chlorine and even nitrogen, phosphorus and potassium. For growth and flowering orchids need three (3) important elements and these are nitrogen, phosphorus and potassium (NPK). They maybe present in water but may not be available to the orchids. A good example is rainwater. Rain water it brings along some nitrogen from the atmosphere but the N cannot be utilized by the orchid in the form. It should be in the form of oxygen or nitrate or in much reduce form or ammonia (NH3). There are nitrogen fixing bacteria and the orchid mycorrhiza, fungi at the roots of orchids living in symbiotic relationship with orchid, both of which can convert nitrogen into a compound that orchids can use. Lightning can produce ammonia which can directly be used by the plants.
The earth atmosphere contain about 78% of Nitrogen. So then, when the stomata of the leaves open, it allow air to get in. Almost three-fourth (3/4%) of that air is nitrogen but he orchid can not utilize N in that form. An orchid is just contented to get CO2 from that air which h it need for photosynthesis. Even though CO2 is only about 0.03 percent of that air, they can get all the CO2 they need.
The other two important elements are phosphorus (P) and potassium (K) usually absorbed or utilized by the orchid in the form of potassium phosphate. There are other elements needed by the orchid but in the trace quantity, and these are magnesium, manganese, iron, copper, zinc and others.
In the wild, we can see orchids growing and flowering. The presence of orchid mycorrhiza or the symbiotic relationship with certain fungi like Rhizoctonia is so important to the orchid. While the fungi seek shelter on the orchid roots, it produce the necessary nutrients needed by the orchid plant. In its natural habitat, the seeds of orchids will not germinate unless infected with such fungi. And orchid pod contain minute powdery materials which are actually millions of seeds. When the matured pod breaks and the tiny seeds extruded, being so minute, they can easily be carried by the wind. When they latter will also produce the necessary nutrients for growth of the young embryo. Most germination, the bean embryo plant will utilize such nutrients for initial growth until it can produce its own by photosynthetic processes. Orchid seeds being so minute, unluckily do not have cotyledon.
So then, the orchids need to be fertilized in order to have the necessary nutrients it need for growth and flowering. There are two kinds of fertilizers, the organic and organic or chemical fertilizers.
Organic fertilizers are those derived from plants and animals. These could be guano (bat droppings), chicken manure, cow dung, animal (or human) urine or compost (decayed leaves, stem, roots, etc. of plants). Traditional orchid growers especially those in the rural areas, utilize fish washing to fertilize their orchids. Such is a good fertilizer but its users are inviting diseases, as decaying fish bloom, flesh and scales will attract insects like flies and ants. It is also common sight to see egg shells stuck in the orchid pots or media, with the idea that the left over egg-white in the shells will serve as fertilizers.
These organic fertilizers will be of importance for the growth of orchids as they are high in nitrogen. If used on matured plants, stem will be longer and leaves broader but may not induce to flower. Except for terrestrial orchids like Spathoglottis. It is difficult to apply organic fertilizers on epiphytic orchids like Vanda. As there are no known application processes so the amount of nutrient applied is unknown. Organic fertilizers when not properly prepared may also contain pathogen which may be detrimental to the health of the orchids.
The application of inorganic or chemical fertilizers is the easiest way to supply the orchid plants with necessary nutrients. If you are a chemist, you will have an advantage as you can prepare a fertilizer to supply the needed quantity of nutrients for growth or flowering. Fertilizers are prepared commercially, depending on the proportion of nitrogen, phosphorus and potassium (NPK) and areas available in plant nurseries or supermarkets. They are usually classified into two categories based on their effect on the plants, as grower or bloom booster. The growers preparation have higher concentration of N, than P and K, like 20-10-10. Bloom booster has the same or lesser quantity of N and P and K like 10-10-10 or 10-30-20. Usually 10-10-10 is called complete fertilizer as it has same proportion and all the NPK elements are present, but this is a misnomer above. Although these other elements are needed in trace amount, their presence is necessary to satisfy the needs of orchids.
Commercial fertilizers have instructions on their application. Usually, a measured quantity is dissolved in a known quantity of water and sprayed on the plants. Frequency of application is also mentioned. The orchid plants absorb the fertilized water readily by the roots, although the leaves and stem also do. The roots of orchids are covered with thick spongy layer called velamen which absorb water and its nut4rients and hold them for a longer time. There is also the slow release fertilizer in the form of small granules, which are applied on the pots or potting media or orchids. During watering, a small amount of fertilizer is released of dissolved in water. These fertilizers are usually applied by commercial growers to save manpower as each application of few granules will last for one or two weeks.
There are also cheap commercial fertilizers with proportionate amounts of NPK, which are used to grow rice, fruit threes and other agricultural plants. These are in the form of granules but these they are not recommended for orchids. These do not readily dissolve in fad water (except urea, which must be used with greater care), while directly applying the granules to the roots will damage the orchid plant.
REFERENCES
Arditti, Joseph. 1987. Orchid Biology. Reviews and Perspectives, Vol. II. pp. 83-118, 173-212, 243-370, Vol. IV pp 105-192, 227-259; Cornell University Press, USA
Collier’s Encyclopedia. 1984. Vol. 17, pp 559-564; Vol 8, pp 765-772, Vol 23 pp 372-330
Davis, Reg S. and Steiner, Mona Lisa. 1982. Philippine Orchids, pp 1-35, Enrian Press, Bulacan, Philippines
PCARRD. 1994. The Philippines Recommends for Orchids. Los Baños. Laguna, Philippines
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