Fertilizing orchids has already been discussed in a previous column. But, in the wild, orchids grow and flower without anyone fertilizing them. How do they manage to grow so vigorously in the wild? They choose to outsource nutrient collection to growth partners; mycorrhizal fungi.
The Symbiosis Between the Mushroom and the Orchid Begins at Birth!
From the moment the seeds germinate, orchids form a partnership with a nourishing fungus. Indeed, orchid seeds contain very few, if any, nutrient reserves, and the developing embryo will absolutely need a symbiotic fungus to hydrate and nourish it during the first weeks of its life. Gradually, the small seedling will develop and build an autonomous root system. Subsequently, this vital link with the fungus will evolve until it becomes optional in adulthood, especially when the main root system is sufficiently vigorous and is implanted in a sufficiently rich growth medium.
This “food” mutual aid relationship may surprise us, but it is in fact fundamental to the entire evolution of the plant world on Earth. The first forms of plant symbiosis date back to around 450 million years ago, when marine algae (devoid of roots) washed up on shoreline rocks and survived thanks to the presence of nourishing fungi. This is in fact the prehistoric form of lichens that we still know today. Slowly, terrestrial plant forms became more complex and improved their main root system to reduce their dependence on this symbiotic relationship with fungi, which was too irregular.
It is estimated that the vast majority of plants on Earth (nearly 80%) rely on mycorrhizal symbiosis to improve their growth and their resistance to certain diseases. In young orchids in the wild, practically 100% of seedlings depend on mycorrhizal symbiosis for their protection and nutrition, but this dependence decreases as the main root system develops.
The Symbiosis Between the Fungus and the Orchid Fluctuates With the Seasons
Thus, once adults, many orchids will continue to draw water and nutrients using both supply networks: the main roots (more durable and strong) and their fungal extensions (more extensive but more variable over the seasons). Although the traditional roots will remain the “permanent and regular” supply channel, orchids will therefore resort to “more seasonal” mycorrhizal fungi that will quickly increase the supply of nutrients when growth needs require it.
So, we can say figuratively that orchids resort to “outsourcing” to feed themselves! In scientific terms, we would say that they are symbiotic, that is, they live in symbiosis with mycorrhizal fungi that do much of the work of capturing water and nutrients. As mentioned earlier, mycorrhizal filaments are sort of thin extensions of the roots that elongate in search of water and, at the same time, capture certain dissolved nutrients and minerals. But that’s not all. Thanks to their chemical transformation capacity, the fungi will also “filter and condition” these nutrients before transferring them to the roots. This is a real boon for the orchid during the growth phase. This work of absorbing and conditioning nutrients is essential for the growth of the orchid – especially at the beginning of its life, as we explained previously.
In exchange, the adult plant will provide carbohydrates (elementary sugars produced by photosynthesis and certain vitamins) to the symbiotic fungi, which will then be able to use them to develop and extend their branches well beyond the plant’s footprint on its support. Both partners will thus find a real advantage in terms of vigor and resistance to environmental hazards. Botanists, specialized in the study of mycorrhizal fungi, estimate, however, that the sugar cost of this outsourcing would be relatively high, i.e. between 10% and 30% of the carbohydrates produced by photosynthesis. It is therefore a significant investment for the plant that engages in this type of mutual aid relationship.
The Symbiotic Relationship Varies Over the Life of an Orchid.
Mycorrhizal filaments are microscopic (often a few microns in diameter, much smaller than a human hair, which measures about 100 microns), but their development is rapid when humidity and temperature conditions are favorable. In the event of a significant disturbance, the fungus reabsorbs and goes into “dormancy” until a new, more favorable season allows it to start again. In the meantime, the traditional roots will provide the plant with a basic supply.
Thus, an orchid that lives for about ten years (which is very likely in nature) will experience several successive generations of partner fungi. These fungal outbreaks will inevitably be interspersed with periods of biological slowdown, a consequence of the reduced water and nutrient supply. In addition, an evolution has often been observed in the succeeding fungal generations – as if a new team of “subcontractors” better adapted to current conditions was taking over the leadership of the symbiotic relationship. Over the course of their lives, several orchids will thus associate with different mycorrhizal fungi, particularly at the beginning of their life and in adulthood, reflecting the different nutritional needs during their existence.
The Mycorrhizal Link Also Allows the Formation of “Interconnected” Plant Communities
Recent studies have shown that the mycorrhizal bond can often “unite neighboring plants” and allow them to exchange nutrients and hormones through their shared fungal filaments! Obviously, the fungus must be compatible with all the plants in the same mycorrhizal network, but this seems to be more common than we think.
In meadows, this plant interconnection has been demonstrated between several plants of different species, some being orchids and others not. In forest environments, some understory orchids could even chemically bond with neighboring trees and thus benefit from the monumental photosynthetic capacity of these forest giants. Even epiphytic orchids succeed in weaving mycorrhizal links with other plants, thanks to the network of mycelium that runs along the surface of the branches on which they are found. These fungal networks are obviously thinner and more variable, but their effectiveness in terms of chemical exchanges has been demonstrated by a few in-situ studies; notably in China, Brazil and La Réunion.
The current state of knowledge does not allow us to explain in detail these chemical exchange relationships between such different plants. However, it is already clear that the formation of “interconnected plant communities” presents concrete advantages, such as access to reserve nutrients stored in neighboring plants and/or the sharing of certain vitamins (or hormones) whose synthesis is easier for certain partners present in the environment.
In summary, the orchid’s mycorrhizal links with fungi, although very discreet, turn out to be much more significant than it seems. First, they allow the germination of orchid seeds, second, they increase nutrient collection when growth needs require it, and third, they promote valuable chemical exchanges with neighboring plants to better manage the contingencies that the orchid will face during its lifetime.
In Domestic Cultivation, It Is Difficult to “Co-Cultivate Mushrooms and Orchids”.
The symbiotic relationship between the orchid and its fungus is established spontaneously in their natural environment and is constantly evolving as their needs change. In domestic cultivation, all of this is difficult to reproduce. There have been a few experiments in co-cultivating mycorrhizae with orchids that seem to have produced very good results, but the techniques used remain very empirical and difficult to generalize. I have great hope for the future of these co-cultivation techniques and hope that well-structured research projects can confirm the spectacular preliminary results. In the meantime, we will have to resort to traditional fertilization if we want to stimulate the growth of our orchids in domestic cultivation.
Thanks
The author would like to thank Louis Paré, agronomist-researcher, for allowing the use of one of his photos illustrating the mycorrhizal filaments attached to a plant root. The author also wishes to highlight the fascinating research work carried out at the Muséum national d’Histoire naturelle (in France) under the direction of Marc-André Sellose, with the support of numerous collaborators. Their work was summarized in a special issue of the journal L’Orchidophile no. 245 (June 2025) published by the Fédération France Orchidée (https://france-orchidees.org/). This work is fascinating and very much appreciated!
Editor’s Note
Mr. Charpentier’s orchid articles are published on the Laidback Gardener website under a legal “Copyleft” format. As a result, republication of his columns is permitted provided that the following credit is added: This article was originally published in french on the jardinierparesseux.com website and in the English on laidbackgardener.blog.
Great article