If you are reading this, you probably already know what coco coir is, and what it means to be “buffered.” If you were simply intrigued by the title (and who wouldn’t be?) the 30 second answers are as follows:
a. Coco coir is the fiber of the coconut husk which has been used for centuries and is quickly becoming a suitable alternative to peat moss and is being widely used as a component of growing media.
b. Buffering, in a horticultural sense, is to lessen or modify some aspect of media such as pH or ability to hold nutrients.
If you skipped a few too many science classes in high school, here is a quick refresher. Particles of organic matter (such as coco coir) are negatively charged on their surfaces. This means that they attract what are known as cations. Cations are positively charges ions. The sum total of negatively charged ions are known collectively as the cation exchange capacity or “CEC”. Knowing the CEC of a media will let you know how much of any particular nutrient the media can absorb before it is leached out. It is important to know however, what the nutrient needs of your particular crop are before setting about adjusting the CEC of any media.
Why Does it Matter?
The CEC of coco coir, if un-buffered can tend to be too high in sodium (Na) and potassium (K) and too low in Calcium (Ca) and Magnesium (Mg). Potassium is good for plant growth, right? Well you can of course have too much of a good thing. Too much K will result in too little Mg being available for your crops. Too much Na is just a bad situation all the way around, especially to young and bare root plants. Coco coir, being of the coconut tree can have a very high level of salts. They often grow along coasts and absorb salt from the water that they grow by.
The level of salts in a media are measured usually as a level of total dissolved salts (TDS) or in units of electrical conductivity (EC, not to be confused with CEC). Of course each crop has different needs, but in general, most media should have an EC of less than 1.0 (in hydroponics applications, EC can be up to 2.0) so that the levels of salts do not interfere with proper nutrient uptake or plant function. If a media is under sodic conditions (high EC), it can be toxic to most plants. In soils, high EC correspond to poor soil structure and poor drainage.
What To Do About it
Manufacturers of soilless substrates are getting better about producing buffered coco coir, with EC’s as low as .5. They buffer the coco coir with a solution of Ca and Mg or just Ca before packaging it and sending it off to your favorite hydro supply store or garden center. If the pH, CEC and salt content of your particular coco coir is not disclosed on the packaging materials, that information should be available by making an inquiry to the manufacturer. This will help you to decide if you need to buffer the coco coir, or not. If you have coco coir that is unbuffered, you can add calcium and magnesium supplements yourself, by rinsing the media with a solution of water, calcium and magnesium, or other nutrients that your particular crop may need an abundance of.
Whether or not to buffer a coco coir media also depends on the application. Using coco coir pots in soil is a different situation than using them hydroponically. When growing in soil, it may not be necessary to buffer at all, as the soil itself may be able to buffer the media. Using coco coir in a hydroponic or soilless situation will likely require buffering, or using a pre-buffered media.
A quick word on semantics. The words “buffer” and “rinse” in regards to coco coir are sometimes used synonymously. It should be noted that simply rinsing coco coir with water, will not serve to buffer it. Rinsing the coco coir may well remove some of the water-soluble salts that are in it, but it will not by itself alter the CEC of the coir. Additional nutrients will need to be added in order to do so.
Reusing Coco Coir
Many growers, in an effort to save money, may consider re-using coco coir media, as it holds up fairly well to most growing conditions. Coco coir loses to some degree, its ability to hold water and nutrients after it has been used through an initial growth cycle. It will serve your crop well to re-buffer the coco coir, even if it originally was buffered upon its first usage. The addition of a non-ionic surfactant, will help the coco coir with its reabsorption capacities. Non-ionic surfactants, sometimes known as “spreader stickers” reduce the surface tension and allow the water to be “wetter” to penetrate more effectively. If you do choose to reuse your coco coir, make sure that whichever surfactant is chosen, is compatible with the crop that you are growing.