Cocopeat and Microbes


Cocopeat or Coconut Coirhas in the past couple of years become a medium of choice for many indoor growers. It is easily obtainable and it is relatively inexpensive. It has a number of advantageous characteristics: a favourable pH; a good moisture retention capacity; excellent air to water ratio; superb drainage; resistance to compaction and it also has the ability to retain certain nutrients. This retention of nutrients is also called the cation (pronounced like “cat-iron”) exchange capacity. As well as all of these characteristics, it is very easy to get rid of at the end of a growing cycle. Simply toss it on the garden or anywhere where there is soil and other growth and it will just rot down and disappear.

New Production System

Cocopeat, in many areas of the world, has replaced true hydroponics as a commercial production system. Where expanded clay, perlite and NFT all provide an inert medium, at least initially, cocopeat is far from inert. It is true, that over time, even these inert media attract a population of microflora and microfauna but it is never as prolific as it is in a medium like cocopeat. Incidentally, the fact that rockwool, expanded clay or NFT develop their own populations of microbes demonstrates the futility of trying to maintain a sterile system. You are simply wasting your time and money. It’s far better to accept the microbes as part of the scene and just encourage the “good bugs” to benefit your plants. As cocopeat is the result of the decomposition of coconut coir, it is full of fungi, bacteria and actinomycetes as well as larger arthropods. However, the cocopeat is dried and compressed prior to sale so most of these organisms are killed. Some do survive as spores, however, and germinate when the peat is moistened. The great majority of these organisms won’t worry your plants and the few that could attack your plants are usually (but not always) overwhelmed by the larger numbers of “good bugs” that are present. After the peat is moistened, more organisms, usually fungi and bacteria, colonise the peat from airborne spores and contaminated dust particles. Bacteria initially become the dominant group of organisms. However, over time, this dominance shifts toward a fungal dominance as the easily compostable material is used up.  In one gram of aged peat there may be as many as 60,000 species of bacteria and fungi.  Fortunately, the end result of composting is a bacteria and fungi laden medium that is conducive to growing plants. It is very beneficial to encourage this activity.

More like Soil

As you can see, cocopeat acts more like soil than any other non-soil medium. The richness of biological life is just not the same in a sterile medium. In the normal hydroponic situation we need to add organisms to the solution to get a similar effect. The biggest danger of an inert and sterile medium is the introduction of pathogenic organisms. If this occurs, then there is no natural defence as there is in a biologically active medium. This then means that your plants are subjected to the full impact of a pathogenic organism without getting any help from the soil microflora and fauna which would normally help the plant fight off the disease.  In any inert medium, where there is no population of microbes, the first microbes to colonise the sterile medium will become dominant and if they are disease organisms, then your plants are in trouble.

To Sterilize or not to Sterilize?

A word here about sterilised cocopeat. There are a few companies who offer steam sterilised cocopeat just to make sure that there are no “bugs”, good or bad.  This approach was favoured from the 1950’s to the 1980’s. Most agronomists now agree, however, that it is far better to use an un-sterilised composted medium. The fact that this approach is now used by the big commercial producers of seedlings and plants should tell you something. There are plenty of references and trials available on the internet for you to read.

Hortlink, Zhang, Han, Stone, Krause and Dick
Ohio State University, 1997

Applied and Environmental Microbiology, October 1998, p. 4015-4020, Vol. 64, No. 10
Copyright © 1998, American Society for Microbiology. All rights reserved.

While all this is interesting, as a grower you don’t really need to pay much attention to it beyond perhaps inoculating the cocopeat at the beginning of the growing cycle with a microbial formulation. This will get microbial activity happening sooner.

The main result of all this composting process is that the cocopeat will get finer and “gluggier” as it breaks down. It therefore pays to discard the cocopeat every year, at least. To be safe, it wouldn’t hurt to use new peat in every growing cycle.

As cocopeat is an organic medium, no two batches will ever be exactly the same. Some will be more decomposed than others: some will be coarser and some will be finer. They will all act just a bit differently each time you use them. However, the differences should not affect your results. The best part about using cocopeat is that as it is an organic medium, it is much more forgiving of mistakes than true hydroponics.