By: Erik Biksa
Courtesy of Maximum Yield Magazine
In North America, a trend in indoor gardening has been a shift towards soilless growing practices versus hydroponics. One of the primary differences in this cultural practice is that plants are watered manually. This is usually accomplished with the aid of a submersible pump, length of hose, and a watering wand delivering the nutrient solution from a reservoir/cistern where the nutrients are prepared. While in hydroponics, the nutrients are mechanically circulated to individual planting sights typically via emitters, sprayers, flood/ drain fittings, etc. Also in hydroponics, there is typically much less growing media which is usually inert, and the nutrients are most often re-circulated.
Traditionally peat based soilless mixes have been the most widely used by growers. Bear in mind that you are much more likely to encounter a peat bog in North America than you are a coconut plantation. Since the supply is already in our backyard, it has been the natural choice.
Peat is typically stripped from bogs. The composition of different peat deposits varies widely, depending on the vegetation from which it originated, state of decomposition, mineral content and degree of acidity (Lucas et al. 1971; Patek 1965). The colour may range from dark black to a light tan depending on the source, moisture content, and other parent material present. Basically there are three types of peat: Moss Peat, Reed Sedge, and Peat Humus. The one most commonly found in commercial soilless blends is the Moss Peat variety, which is most often milled from Sphagnum moss. It is relatively inert, light in weight, holds up to 10 times its weight in water, is acidic, has some cation exchange capacity (CEC), and contains little if any beneficial nutrients. Bogs are a relatively “non-renewable” source of growing media when compared to coconut coir.
Coco coir is the fiber that results from the processing of coconuts (the removal of the “nut” from its fibrous encasing). The coir fiber is a by-product of an existing process and is quite renewable when compared to peat moss sources. The fiber is arguably more bio-active than peat fibers resulting from bog conditions. The coconut, as we know it from the grocer’s, is surrounded by tough fibers in a green casing where it is attached to the tops of coconut trees swaying in the breeze in tropical conditions. The coconut tree is a well adapted plant, in its ability to populate an area through the “seed”; the coconut. As the coconut matures on the tree, it breaks free and may fall a considerable distance. It may roll down an elevation before coming to rest, or it may become water borne and float for many months and wash up far from its origin. In any case, the coconut is able to germinate and root itself in sandy and often saline (salty) conditions miles away from its parent conditions. We are talking about a 6 to 8” high octane seed here! As a matter of fact, sterilized coconut milk is often added o the growing media as a source of hormones and nutrients in plant tissue culture.
The coconut is teaming with naturally occurring growth hormones and other bio-stimulants that are inherent to the survival of the species, which fortunately for growers may be found in the fibers surrounding the “seed” which may be processed for use as a growing medium. As with peat, there are factors affecting the quality of use of the coir as a growing medium. The origin and age of the parent material largely plays a role in the fiber qualities. Coconuts harvested when fully mature contain more lignins and cellulose. These fibers are tough and durable enough to manufacture rope from. Interestingly, coconut fiber is the only natural fiber resistant to breaking down in salt water. This helps make it ideal for indoor gardeners, as nutrient solutions, particularly popular inorganic varieties and the salts they contain, play a role in the erosion of growing medias over the course of the crop.
After coconuts are harvested, the fibrous husk is removed from the coconut “seed”. An interesting fact about coconut harvesting from the Royal Botanical Gardens, KEW website: “…in some coconut-growing areas in Indonesia and Thailand the pig-tailed macaque monkey (Pithecus memestrinus) has been trained to climb the trees to collect the nuts. The monkeys are well-treated and prized for their skill….”
After the coir fiber is separated from the nut, it is then soaked in slow moving pools or streams to moisten it, allowing for further separation and processing. If the coir fiber is intended for high value horticultural crops, care must be taken to remove salts. Often these streams are near or contain saltwater. Some sources of coir are high in sodium, as a result of poor conditioning. “Double washed” coir fibers tend to have significantly lower levels of impurities such as sodium.
To help determine the quality of your new and unfertilized coir fiber, flush 1.5 liters of distilled water through 1 liter of growing media, and measure the runoff with a dissolved solids tester. This is based on the Dutch RHP method of analytical procedure. Chart 1-A illustrates the final analysis of two coco coir samples that are well suited to growing applications based on their salt content. Note that the test does not provide information as to the structure of the coir, just specific ions as impurities. Both samples have significant levels of soluble Calcium, Magnesium, and Potassium, suggesting that they have been pre-treated to satisfy the CEC requirements of the soil.
An overall value of 150 ppm or less characterizes a very pure material, while values up to 500 ppm have likely been treated to condition the media. Values greater than 500 ppm should be suspect in containing excessive sodium levels. Sodium levels should be kept as low as possible. Levels at over 100 ppm would be considered excessive and over 250 ppm are considered toxic.
I have spoken with several growers who had tried coconut coir as a growing media several years back when it was first being introduced to the indoor gardening marketplace. They did not continue to use the media, and switched back to peat based soilless mixes. After working with some of the older coconut coir available I can see why. Firstly, the earlier coco coirs available contained extremely high levels of sodium. In one batch tested, the leechate was over 1000 ppm! Keep in mind, that’s with just fresh water being run through the containers. Also the fiber quality was very poor. The coco was lighter in colour, suggesting immature fibers. The result was a powdery growing media that had poor structure for root growth and aeration. Coupled with high sodium levels, the crop was limited from the day it was planted. The coconut coir available to indoor gardeners in North America today is usually leaps and bounds ahead of the coir that was available just a few years ago.
Coconut coir that is optimal for plant growth also tends to be near neutral in pH (7.0). This helps ensure proper ionic balances in nutrient solutions, as fewer additions of pH adjusters are typically required to compensate for the pH of the growing media (i.e. rockwool has a very high pH).
Coconut coir as a growing media can be purchased in either loose or dried and compressed forms. The loose forms are already hydrated and are usually ready to be added to containers or raised beds for planting. The compressed forms require hydrating. Although the hydration process may be laborious, the dried and compressed blocks are much easier to transport to and inside of the growing location. The blocks are ideal for remote outdoor gardens. In compressed form, the blocks typically take up about 1/5th of the space as commercial peat mixes, and are much lighter in weight. For example a 5KG block of compressed coco coir measures about 10” X 10” X 4” and when expanded yields near 72 liters of high quality growing media. That’s enough to fill nine 2 gallon pots; one block per 1000W HID lamp.
Some coirs have been chemically treated, this is most often the case with loose pre-hydrated varieties versus compressed blocks. The treatment has been done to satisfy the cation exchange capacity (CEC) of the growing media. As a refresher, “cations” are positively charged ions, such as Calcium, Magnesium, Sodium, and Potassium. This means that the growing media will hold these ions in a matrix, releasing them as required by plants. There is one slight drawback to this. Until the cation exchange capacity of the growing media is filled, the growing media may hold positively charged nutrient ions, most notably calcium, in reserve, making them less available to plants. However, the cation exchange capacity (CEC) of the coir media is quickly filled, and actually assists calcium absorption in the crop cycle. To ensure optimum availability of all nutrients, supply additional calcium during the first week of growth or during the hydrating process of the coconut coir. Calcium supplement products are ideal for this. Some nutrients specifically formulated for coco tend to have elevated levels of calcium and magnesium while having lower levels of nitrogen.
Coir is the ideal growing media for organic and hydro-organic applications. The air volume retained harbours greater populations of beneficial (oxygen loving) soil organisms than peat mixes. Increased population levels of soil micro-organisms play a strong role in high yielding organic gardens.
One of the most impressive attributes of coconut coir as a growing medium is the level of aeration and structure supplied to the rootzone. A coarse, good quality coir is difficult to over water. Basically, if you supply too much moisture it will just run out the bottom of the container, and will not become water logged (anaerobic) like peat based mixes may. The coconut fibers are much tougher and coarser than those of peat. This means more airspace is available for drainage and to supply the roots and soil life with higher levels of atmospheric oxygen (O2). Coir fiber will not compact over the course of the crop as with peat. With peat, we all remember filling the pot right to the top at the start of the crop, only to find that a third of the media is “gone” by harvest. What is happening is that the peat fibers are eroding from the force of watering, saline conditions, and the roots compacting the media. This robs the crop of valuable air space in the rootzone, and increases salt build-up as drainage is impeded. With coir fiber there is little if any compaction of the growing media over the cropping cycle due to the higher content of lignins and cellulose found in the physically coarser fibers. In container grown crops, little compaction is evident. Plants receive optimal water to air ratios over the course of the entire crop, not just the first few weeks.
Coconut coir is the ideal choice for raised bed production for several reasons. Firstly, many raised beds have been constructed without drainage. Moisture and nutrient management become much more temperamental in this type of growing situation. If you over water, there is much less of a chance of drowning roots. The coir fiber will retain airspace throughout the growing media, and the excess moisture will pool at the bottom, where it may wick up through the growing media, as coir tends to have excellent capillary movement for moisture and nutrients. To see just how resilient the air space is in coir, pick up a handful after thoroughly soaking and squeeze the material. When you open your hand, you may be surprised to find the media springing back like a sponge. Try this with peat, and you will not see any memory for macro pore space. Also, the coir fiber is resistant to breaking down under saline conditions, such as those found in non-draining raised beds, particularly those that are re-used over several crops. If the growing media is to be re-used the coir fiber will resist breaking down from mechanical handling (i.e removing old roots, mixing in growing amendments), while peat tends to become not much more than dust after several cropping cycles. In Holland, coir has been used to grow long term crops such as roses for periods longer than 10 years! The cation exchange capacity of the coir fiber also helps to reduce the incidence of salt burn, as it offers some buffering against positively charged ions such as sodium. When re-using any growing media, impurities such as sodium tend to accumulate over time. Organic based nutrients allow for a longer periods of use over multiple crops, as they tend to have less salts as impurities.
Unlike peat, coir may be used in re-circulating applications. In re-circulating drip systems it is recommended that the fiber be mixed 50/50 with either coarse perlite, pumice or grow rocks for faster drainage. Coir is also very suitable for flood and drain applications. There are coir products now available in the hydroponic marketplace that are excellent substitutes growing mediums. One such product is a small, plastic wrapped square of compressed coco coir. Once hydrated it expands into a 6” X 6” X 6” growing cube. Moisture management may differ from other media. Another benefit is that coco tends to have a near neutral pH value, so lesser quantities of pH adjusters are required in the nutrient solution. Excessive additions of pH adjusters may create an ionic imbalance in the nutrient solution, locking out or precipitating some nutrients.
One of the greatest benefits to using coco products is that disposal is easy and environmentally sound. The coir makes an excellent and natural looking top dressing to outdoor flower and vegetable gardens.