Coco is fast becoming a favourite medium for crop production worldwide, but is still relatively new to the industry. Although it was first brought to the attention of the Royal Horticultural Society in the nineteenth century, it was not until the late 1970s and early 1980s that it began to carve a niche for itself. It took some time to establish itself primarily due to the lack of understanding of both the chemical and physical properties of the product. Once the properties of coco as a medium were understood and growers started to understand how to use it correctly, its popularity took off. So what are the potential pitfalls of using coco as a medium? What follows is a brief discussion of some of the issues that can arise, and possible solutions for those issues.
Some basic properties that you should know about
We should never forget that coconut trees are capable of actually ‘drinking’ sea water. They have developed the ability to concentrate excess ions in the areas surrounding the cells, which allows osmosis to continue and water to move into the plant from the high-EC sea water. It is this ability that gives coco its characteristics, both positive and negative, when used as a plant growth medium.
This attribute also allows the husk tissue to be very stiff and slow to decompose so that it is able to protect a developing embryo and future tree as it floats around the ocean for a long period before germinating and landing on a new beach. In so doing, it allows the coco tissue to have both a known content and a known path for decomposition of acceptable duration, enabling the development of a system for usage. It also allows for a known structure to exist for a known amount of time giving the physical attributes necessary of a good medium.
These physical characteristics include fibres and a break-down product known as coco peat. Once the edible part has been removed, the husk of the nut is softened and then the fibres are torn away. This produces long fibres that are very stiff and can be used to make items such as door mats and brooms, as well as shorter fibres that provide a ridged structure and give the coco its characteristic porosity. Dust or coco peat is also released; this is made up of smaller particles that act like tiny sponges. The coco peat component of coco growing medium not only improves its structure, it also provides a great deal of water retention. After the right amount of time being composted and processed by movement and regular rinsing, the consistency of the peat reaches its best and its chemistry is more stable and suited for growing. However, its chemistry is still not fully correct and needs to be adjusted.
Once the husks have been soaked and torn apart, the decomposition process accelerates. The concentrated ions (salts) begin to be released very rapidly. Careful processing and timing assist this process until the rate of release falls back into acceptable limits and the coco can be used for growing. In the process of this break-down, the sites that release ions such as potassium, and sodium remain in place and function as Cation Exchange Sites (CEC) to which a useable plant nutrient can attach itself, as also occurs in good mineral soils. At this point, the medium needs to be processed by buffering with a product designed to control pH and protect the ratios required to maintain the availability of these elements for plants. This process was also mentioned in the previous article. These excess ions or salts are released for as long as the coco continues to decompose and the process must be managed continuously.
The main things to watch out for when using coco medium for use in growing include:
- Choose coco that has been correctly treated and is of a consistent quality in both chemistry and physical structure.
- Use coco that has been properly aged to maximize the efficiency and quality of the product.
- Select coco that has been correctly balanced through a buffering process tailored to the characteristics of individual batches of product.
- The availability of a nutrient designed to feed the plant and to manage and adjust the continuously decomposing coco medium.
While there are many other aspects to consider, these are important to bear in mind for the rest of this article.
Producing a good-quality coco substrate is an intensive process that takes months. To be able to use the product as a growing medium, the substance derived from the coco husks needs to be aged, washed, treated and rinsed. If this process is not carried out, or not carried out correctly, there is a risk of lacklustre growing results or potassium or calcium deficiencies.
Once this process has been completed, the coco has to be dried so that it can be pressed and made ready for shipping. The drying process is obviously dependent on the prevailing weather conditions, so good producers will ensure that they have enough coco product stocked up to see them through the rainy season or any shorter wet periods. Producers also need to take precautions against the risk of impurities or inadvertent contamination. For example, the coco is susceptible to contamination with (tropical) weeds or human pathogens, or it could become mixed with coco that has not yet been aged or other substances such as sand. Any of these impurities could cause problems when the product is used for growing.
To prevent contamination, good coco producers will take steps to protect the coco as it dries, such as using protective screens, cleaning the drying area, checking samples of the product in a laboratory, using storage facilities and following appropriate procedures. The two photographs above (Picture 1 and Picture 2) show examples of good and bad drying areas – on Picture 2 you can see a drying area where effective precautions have not been taken, meaning that the chance of impurities is much greater. On Picture 1 you can see a concreted drying area where the risk of contamination with impurities is being minimized.
Growing in coco – trouble-shooting
When the right coco is used as a medium, it is possible to achieve some pretty exceptional results, and not all the mechanisms behind this are understood yet. Research into the properties of coco continues every day. Faster growth, healthier plants, lush foliage, and adaptability have all been used to describe successful trials with the product. It has long been known – and recently substantiated – that coco as a medium promotes plant health because of specific factors found in the product and by the micro-flora and fauna that develop in coco medium. In coco, the availability of the nutrients applied is unusually high because it does not bind or affect these nutrients. It also provides pH control without additional liming requirements between successive crops. However, none of these benefits will occur without correct buffering before use. After that, the buffering is best maintained over time by applying the right nutrients in the right way.
However, using bad coco is a recipe for disaster and much more hard work. Sterilising the coco incorrectly by harsh steaming or using toxic chemicals will destroy the beneficial characteristics of the product. If the product is not rinsed before it is packaged, or not rinsed correctly (too little or with bad water), high salt levels will be left behind. Failing to buffer properly leaves huge holes in the chemistry of the medium. Green or old coco is equally problematic and inconsistent in its composition and the consequences can vary from a wildly fluctuating EC and pH to an unstable and rapidly changing physical structure. Salts are given off constantly (such as sodium, potassium and chlorine) and they must be removed or their effects neutralized. A great deal of work and preparation goes into the successful use of coco as a growing medium.
One of the biggest issues with coco is watering. Coco acts like a sponge, absorbing and holding water. And just like a sponge, water comes out when it is squeezed, but not all the water. The sponge remains damp and coco may appear wet, and yet there may not be enough water available for the plants. On the other hand, constantly watering coco will result in over-watering and in fact when you are using coco, you need to water at a minimum of 50% dry and 70% dry may be better especially during the first weeks of growing when most of the roots are formed. This is because roots need oxygen as well as water, and where there is water, there is no air. A sophisticated and reliable method of measuring the amount of water in the coco substrate that is available to the plants is using a tensiometer (pictures 3 and 4). This is a device that determines the water potential in a substrate – effectively the force needed to release the water from the substrate. This takes the least force in substrate that is saturated with water and the most when the substrate is completely dry.
There is an easier and cheaper way to determine the amount of water available to your plants, however. You can determine the amount of water available to your plants by thoroughly watering a container of plants and coco medium and weighing it after the water has drained. Allow the plants to dry out until they reach wilt point and weigh the container again. The difference between the two weights is the water available to plants. When 50 - 70% of this amount has been used (you need to weigh the container), it is time to water again. It is never good to allow plants to wilt, but an experiment may make it worthwhile. If plain water is used on established coco, the buffer will be upset and the next issue will arise.
The chemical balance in the coco is critical in three ways. First, the pH of the coco as a natural product is not ideal and needs to be adjusted. Second, the CECs that we mentioned earlier are not the real CECs in the classic sense, because while they will loosely hold monovalent cation elements (ions with a single positive charge) on a matching negative charge, they will bind a divalent ion such as calcium or magnesium more tightly, making them unavailable to the plant. They also come and go as decomposition moves forward. Third, the release of other ions by coco as it degrades upsets the ratio of elements to each other, causing many of them to become unavailable. The buffering that we have already mentioned fixes this issue temporarily by filling the sites with divalent elements while stabilizing the pH within the range desired and fixing the correct ratio of elements to each other.
If the water used to mix the nutrients is very soft, the concentration of nutrients will need to be higher or the coco will rob the nutrients and calcium deficiency will begin to occur. This is precisely because of these issues. With the popularity of reverse osmosis systems sky-rocketing, this issue is seen more and more often. Growers plan to use pure water, feed lightly to avoid burn and feed often to keep things pumping. This can be avoided, however, by adding back some of the original water to buffer the water once more. There is no other effective cure and throwing a calcium or magnesium product at the problem will just make it worse over time. Adding a higher concentration of nutrients is a better and safer option.
Most importantly, the buffering process applies what we could think of as a coating on the coco which allows the coco to reach the correct pH but does not affect the availability of nutrients so much. The coco is constantly changing as it decomposes and this ‘coating’ must also change and adapt. Using nutrients that are designed specifically for coco growing is a critical part of this adaptation process and crucial to maintaining the buffer. Using some other ratio or combination of nutrients will not maintain the buffer. This includes using plain water, which causes the EC to drop and the buffer to disappear. Equally important is following the feed chart and testing the coco correctly.
Standards are not absolutes but markers by which things are measured. A foot is a foot because it is known as a meter is a meter. In order to get the true picture of the condition of coco in terms of its EC and pH, there is only one correct way and that is the correct extraction method with barium chloride in water. Barium, a bivalent metallic alkaline earth metal, binds strongly to the surface of the coco releasing virtually all the previously bound cations: sodium, potassium, calcium, magnesium and ammonium if present. The level of cations in a barium chloride extract is a good measure of the quality of the substrate at that point in time and enables us to make a prediction of which nutrients were about to be released by the coco substrate, making them available to the plants.
Measuring drainage or run-off alone will never be accurate. It may give the grower an idea based on experience but that is all. Growing means knowing, and correctly measured coco should match the characteristics described.
Some other issues or questions seen when using coco include nitrogen binding and ways to increase aeration. Many growers enjoy using coco more than once, but for successful growth, the coco needs to decompose a certain amount before being used for the next crop. If the first crop fails or is too fast, then nitrogen will tend to bind into the coco causing a week or so of nitrogen deficiency symptoms to appear.
Finally, some growers insist on adding perlite to the media to ‘loosen’ it. Perlite is about identical to coco in physical characteristics and is not liable to do anything for porosity but it will affect the overall chemical profile.
In the end, it is probably best to find a company that has decades of research into coco, that provides correct solutions, and that has introduced coco use into this market. Trust in their experience, use quality products that are well researched, and keep it simple.
