Coco Coir Explained
Best Seed Bank takes a detailed look at the rise and rise of coco coir as a hydroponic growing media.
The glorious coconut has been providing us with much more than the odd Piña Colada for centuries. Traditionally, coconut coir (the outer fibrous husk) has been the backbone of “Welcome” doormats, brushes, sofa stuffing and horticulture for well over 100 years but, as far as hydroponics is concerned, coco coir started to make a name for itself during the late ’80s and early ’90s as a substitute for peat and rockwool, both non-renewable resources. In a nutshell (sorry, couldn’t resist), coconut coir is an environmental by-product of the long-established coconut industry. It’s a 100% renewable resource and the environmentally friendly alternative to bog dredged peat moss.
So what is it about coco coir that makes it such a popular replacement for peat and as a hydroponic medium in its own right? Firstly, check out its outstanding water and air holding capacity. Unbelievably, coco coir can hold eight to nine times its own weight in water! More importantly, coco coir holds a lot of air, in fact even when saturated it typically still holds around 22% air. In this respect it is superior even to rockwool, the world’s most popular hydroponics medium. Rockwool is a great medium but some beginners can easily run into trouble as it typically only holds around 10% air, leaving plant roots in danger of becoming oxygen deprived, particularly when the nutrient solution temperature is over 68-72°F (20-22°C). (The warmer a nutrient solution is, the less dissolved oxygen it can hold.) With coco coir, however, this type of overwatering (or, to put it more precisely, oxygen deficiency in the root zone) is avoided by the enormous amount of air that good quality coco coir can hold.
The amazing properties of coco coir don’t end with excellent water and porosity. Oh no! The best aspects of coco coir are far more varied! Did you know that coco coir possesses antifungal and root promoting properties? As coconuts spend long periods of time floating in the sea before they beach themselves and sprout a lovely new coconut tree, their physical dynamics have to be incredibly tough and unique to survive such a harsh, salty environment and still be able to sprout and grow when the time arises. These properties are available for you, the indoor gardening aficionado, to freely exploit in your quest for your perfect indoor garden. Recent studies have shown that coco coir has a great ability to suppress and protect plants from phythium and phytophthora, two very unpleasant root diseases that can quickly ruin your crop and put a real dampener on your day, week or month! This is very helpful if you are using organic-based nutrients, as these can contain high levels of urea that can build up and burn your plants.
Qualities of Coco Coir
- Coco has ideal pH in the range of 6-6.7
- It holds 8 to 9 times its weight in water
- It holds 22% air even when fully saturated!
- It has excellent drainage and air porosity for better plant growth
- The top layer always remains dry, leaving behind no chances of fungal growth
- It never shrinks, cracks or produces crust
- It aids in suppressing fungus gnats, to a degree
- Excellent cation exchange
- Its anti-fungal properties help plants to get rid of soil borne diseases (inhibits pathogens like phythium and phytophthora)
- Extremely easy to re-hydrate after being dehydrated
- It is a 100% renewable resource
- Completely environmentally friendly
So what makes good quality coir?
There are three parts to a good coco medium: coco fiber, coco pith (coco peat), and chips. Each part brings its own attributes to the table.
Coco pith / coco peat holds a large amount of water but is smaller and facilitates much less capacity to hold air. It is more lignin (woody) and decomposes very slowly. Properly aged, it contains the complex that holds potassium and sodium until it is fertilized and a stronger ion, usually calcium, bumps these off, thereby locking up the calcium and freeing large amounts of harmful salts. Proper aging of this coco pith is critical. It affects the crop time since a minimum amount of time is required to make this usable, at least four months, which reduces the amount of time available for use.
Fiber holds little water but increases the capacity to hold air; the more fiber you see in your coco mix, the more often you will need to water it. Fiber is largely cellulose and degrades fairly quickly. This degradation has an adverse affect on the stability of the medium. The length of these fibers is also critical to these functions as well.
Coco chips combine the properties of the fiber and pith; they are approximately the same size as the fiber and positively influence air-holding properties while holding water. Chips hold less water than pith or fibers. They have the highest air to water ratio of all three parts. Achieving the correct ratio of these components is critical in developing a well-drained, well structured medium for growth, just as the proper preparation of the chemical characteristics is important by buffering the blend before use. (Hydroponic-grade coco coir growing medium has been treated so that unwanted potassium and sodium has been removed. This helps to ensure that the nutrients you later add to the coco coir can actually be used by your plants.)
Storage and Sterilization
Coco is usually stored in giant piles for a couple of years at its country of origin. Unless stored carefully, these huge coco piles can be susceptible to colonization by unwanted pathogens (partly due to the pH of the coco being favorable to pathogens) so, in this case, the coco must be steam or chemically sterilized in order to make it suitable for horticultural use. However, chemical sterilization can have adverse effects; and steaming destroys the structure of the coco peat while converting any nitrogen present into a toxic form, nitrite nitrogen; both destroy any beneficial organisms that are usually present. So what’s the solution? A coco coir supplier needs to control the coconut from harvest to bagging, remove the opportunities for unwanted seed and pathogen contamination, and carefully control the aging process directly. Only then will they stand a chance of producing the cleanest, most alive and most productive form of coco coir. Regulations vary between countries with regard to sterilization (Australia is very strict). Shipping microbes across continents is frowned upon by customs agencies. Some brands are inoculated with specific microbes that are either allowed to cross borders or are blended after landing on the shores where they ultimately will be used.
Finally, caring for the product through proper storage and packaging is critical, after preparation and again after packaging. Storing it too wet speeds decomposition. Drying in big mechanical driers can also have a detrimental effect on structure. In short, improper handling will drastically reduce the ability of the product to provide the correct root environment for proper root growth. Finally, consistency: a grower needs to be sure that they are growing in the same material crop after crop to ensure success. Imagine the heartache of losing a crop because the salts were not properly washed off your latest batch, or the coco peat is too decomposed – this REALLY happens!
So don’t be afraid to ask questions of your coco supplier. Look for an established supplier that sun dries the coco, one that incorporates the correct coco pith, coco fiber and coco chip fractions to get the best blend. This is specific to the grower’s irrigation system, the plants being grown, and the size of the pots used. For instance, you wouldn’t grow orchids in fine coco pith as they require lot of air! Conversely, any fast growing vegetable in warm conditions would enjoy lots of coco pith in the mix. Look for coco that is clean and washed correctly, one that is packaged and stored correctly, and one that is correctly aged.
Let’s take a look at how this natural product should be prepared by the manufacturer. This is the biggest concern in selecting coco coir for hydroponics use. The outer fibers of the coconut are removed by soaking them in water. This soaking process involves either the use of fresh water or, more commonly, the use of tidal water which can be very high in salt. As coco coir has an excellent cation exchange ability it tends to hold onto things like salt which, when used in a hydroponic or indoor set up, can wreak havoc on your plants. Good quality, hydroponic grade coco coir will have not have a high salt content, but you should always flush it through with a low EC nutrient solution before use until no more tannins are coming out. Tannins can easily be seen as they stain or color the water brown. Some indoor gardeners check to see if the PPM of the water coming out of the coco is the same as the water they’re putting in – but a more reliable method is the 1:1.5 extraction method which better determines the actual pH and EC of the coco itself.
The 1:1.5 Extraction Method
A reliable method for measuring the nutrient levels in coco coir is using the 1: 1.5 extraction method. EC and pH of the root environment can be determined by using this method. The pH and EC of the drain water generally deviates from the actual root situation, as coco coir is able to retain and release elements.
1) Take a sample of coco. This can be done with a soil core sampler or a trowel. To get a representative sample the coco must be collected from as many places as possible.
2) Collect the sample in a bowl and determine whether it contains the right amount of moisture. The coco has the right amount of moisture if moisture disappears between your fingers when you squeeze it. Add de-mineralized water if necessary and mix the coco.
3) Take a ½ pint (250 ml) measuring jug and fill it with just over 4 fluid ounces (150 ml) of de-mineralized water. Add coco to the ½ pint (250 ml) mark.
3). Fully mix and allow the slurry to settle for at least two hours.
4) Mix again and measure the pH.
5) Filter this material out and measure the EC of the water remaining.
The target values for EC are between 1.1 and 1.3 (of course, lower is acceptable too!).
Target values for pH are between 5.3 and 6.2.
Reproduced with permission. Copyright CANNA.
I think the best way to get the maximum benefit from coir is in pots, as a direct replacement for rockwool or peat based mediums. Since coco coir holds so much air and water, it is a good idea to capitalize on this by placing a shallow layer of clay pebbles, such as Hydroton, or clean silica rock on the bottom. This provides excellent drainage and, more importantly, causes a huge amount of air to be pulled though when you water for feed. This assists in allowing the maximum amount of air possible into the root system and assists in pushing out the old water or feed solution.
The best way to irrigate coco coir in pots is via drippers. This is the best way to ensure that the growth media remains consistently moist (but not overly wet).
There are a number of manufacturers out there who offer a ‘coco specific’ nutrient formula. These specific formulations are based on the tendency of coco coir to hold onto phosphorus, while only holding a little calcium, while giving off small amounts of potassium. The best nutrient formulations for coco coir will therefore have some extra calcium, but not too much as it will compete for potassium uptake resulting in a potential for potassium deficiency. So are they any better? Well, generally speaking any good, complete hydroponic nutrient is more than suitable for coco coir as these invariably contain all the calcium needed to provide for excellent growth in coco coir. However, for best results, a purpose-made nutrient is best. When feeding nutrients to plants grown in coco coir, aim for a pH of around 6.0 as this will allow maximum availability of all nutrient elements. Remember, a slightly fluctuating pH is a good thing (say between 5.5 and 6.5) as it opens the doors to different nutrients. As for feeding times and frequency, that is really going to depend on what type of system you are running; but for those replacing their peat mix or rockwool with coir there is essentially nothing you need do differently, as far as feeding frequency, flushing, et cetera goes.
So there we have it. Coco coir is an amazing and renewable medium that is ‘top class’ for both performance and benefits. So go on and try this amazing medium, you’ll be glad you did.
Geary Coogler, B. Sci. Horticulture, HORTISOL North American Research
Adam Hanscom, General Hydroponics