Without going into detail (which would be rather complex), I am going to give you a brief personal overview of photosynthesis to help you understand how orchids (and plants in general) work and thus learn how to grow them better. I promise to keep it simple!
Plants Are Mini Chemical Processing Plants
It is the process of photosynthesis that is at the root of all plant activity. It enables the plant to capture solar energy and transform it into chemical energy that is circulated throughout the plant to fuel all the processes necessary for its growth.
Thanks to photosynthesis, the plant combines carbon dioxide (CO2) and water (H2O) to form a new, more complex molecule: a simple sugar or carbohydrate (C6H12O6). This carbohydrate will serve as chemical fuel for a range of biochemical reactions in the roots, leaves and flowers, and possibly even for the composition of the subtle fragrance that will enchant pollinating insects.
Water Is Both an Ingredient and the “Lubricant” of Photosynthesis
Photosynthesis is a “watery” chemical process, meaning that it takes place in a “liquid” solution – bathed in water and nutrients captured by the roots. The water therefore provides a medium for the process while contributing directly to the chemical reaction it supports. The water supply is provided by the roots and is transported to the foliage by a highly efficient system of vessels. As with all chemical reactions, the temperature of the solution will have an impact on the speed of the reactions and on the stability of the intermediate compounds.
The Foliage Will Take Care of the CO2 Supply
Carbon dioxide (CO2) is in the atmosphere and is not captured by the roots. As a result, the plant will have to capture it from the atmosphere by binding it to other chemical compounds, in order to suspend it in the sap with the other ingredients of the reaction. It seems easy, but it is not at all. Several biologists who have studied orchids believe that the main factor limiting the growth of tropical plants is the relative inefficiency of plants in obtaining CO2.
An important detail: CO2 is captured by the foliage through small openings called stomata that are found under the foliage. Depending on the surrounding conditions and the metabolic needs of the plant, the stomata may open to let out the oxygen produced by photosynthesis and/or engulf tiny puffs of air loaded with CO2.
Unlike animals, plants do not have elastic lungs to inhale and exhale. Gas exchange is mainly by gaseous diffusion, a slow and laborious process.
In nature, the wind (or any other movement of air) greatly aids the process of gas diffusion by carrying away the emitted gases and renewing the air near the stomata. In domestic cultivation, it will often be necessary to add some ventilation around our plants to reproduce this process, which is so beneficial to plant respiration.
The Light Will Then Stimulate the Chemical Reaction of the Ingredients
Once all the ingredients are combined in the solution, a series of chemical transformations will begin to gradually agglomerate the water and CO2 molecules until they form our famous carbohydrate (or elementary sugar). Surprisingly, the light (or luminous) phases will have to alternate with dark (lightless) phases to allow all the chemical reactions of photosynthesis to take place.
The intermediate molecular structures will thus be charged with microdoses of light energy (that of photons) and then chemically digest them before being able to absorb others. It is mainly red and blue photons that are absorbed by chlorophyll. Green light will be reflected by the foliage, giving it its characteristic green color.
Subsequently, the simple sugars produced by the process of photosynthesis will be circulated in the orchid via a network of smaller vessels, but generally parallel to those of the sap coming from the roots. Occasionally, you may see some sugars exuding from a vigorous orchid, which will tell you that the plant is functioning at full capacity.
Here Are a Few Lessons to Remember
Although the detailed operation of the plant is relatively complex, it should be remembered that there are four basic needs to be met for the cultivation of orchids and plants in general!
1– Light Is the Energy Source That Makes the Plant Work.
The right amount is needed to properly stimulate photosynthesis, but not too much, which could damage the fragile plant tissue and cause a certain “photon indigestion” in plants with slow chemical transformation. To properly complete the day/night (light/dark) cycle, care should also be taken to provide good darkness for orchids, as certain stages of photosynthesis may be disrupted by stray light during the dark phase.
2– Water Has the Dual Role of “Lubricant” and “Primary Ingredient” in Photosynthesis
Here too, it is necessary to measure out the right amount to ensure regular hydration, without excess, which could asphyxiate the roots and cause the plant tissue to rot. As we explained in a previous column, watering orchids should alternate between hydration and dehydration to allow for gas exchange and limit bacteriological proliferation.
3– CO2 Is the Second Ingredient in Photosynthesis and Is Just as Important as Water
However, it is much more difficult to capture, being in the atmosphere. Without a good supply of CO2, the plant will “suffocate”, just as we do when we lack oxygen. This is often the least well understood plant requirement of orchid lovers! In intensive cultivation, aeration of the growing spaces is often necessary, especially if the plants are fast-growing under intense light flux (i.e. highly stimulated plants).
4– Ambient Temperature Acts as a Regulator of the Plant
Once again, it is necessary to carefully adjust the temperature modulations to harmonize them with the needs of the cultivated plants. In several cases, a drop in night-time temperature is essential at certain stages of chemical transformation, i.e. during the digestion of photons absorbed during the day.
Remember that in order to function properly, the plant will need its four basic needs to be adequately met. It is necessary to consult good references for any new acquisition or to ask your supplier for advice in order to ensure a complete and suitable environment.
Philosophical Epilogue
According to the Bible, Jesus could turn water into wine. Everyone is free to believe it if they want to. However, what is certain is that plants can turn water into sugar! That’s not bad… what do you think?
In fact, these carbohydrates produced by photosynthesis are at the root of all life on Earth. Plants can grow thanks to the chemical energy of these energizing sugars. Animals feed on plants. The caloric content in plant tissue allows them to develop and live actively. Even fungi and mold feed on the energy residues present in the transforming tissue.
Perhaps we should be more aware of and more grateful for the small miracle that is photosynthesis. Especially since it eliminates excess CO2 in the atmosphere while giving us back the oxygen essential to animal life. At least the Bible will be right about one thing: the essential is often invisible.
Editor’s Note
Mr. Charpentier’s articles on orchids are published on the Jardinier paresseux (Laidback Gardener) website under a “Copyleft” legal model. Horticultural societies that wish to do so may include his articles in their technical journal or simply distribute the internet link to their members. However, please include the following statement:
This article was originally published in French on the website Jardinier paresseux and in English on the Laidback Gardener blog.
I have never purchased an orchid, but am given them as gifts from time to time. When I worked in an office on the north east side of a building with very large windows, the light requirements of the orchids seemed to be perfect I had several which bloomed regularly. Now that I am retired, I find my home windows do not provide ideal light and it has been disappointing, although I have been able to maintain a couple that bloom for me. They also have to share window space with other cherished plants. This article has been very helpful in understanding the amazing orchid.
As a collector of white moth orchids, I found this article very illuminating and likely to make me a better orchid grower. Thank you!
Thank you for a solid review of this brilliant process that labors silently around us. Far to easy to take for granted and miss the Genius of Creation .