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Coco Coir
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.
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