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Coco Substrate and Hydroponics

 

When I first published Integral Hydroponics in 2002 I had no idea that the book would go onto sell, to date, over 100,000 copies globally and become the Australian and New Zealand hydro industry bible. In simple terms, my humble scribblings went on to influence many thousands of growers, when, in fact, I had first written the book to supply to my own hydroponic store customers (perhaps estimating that we’d sell a few hundred copies a year).

 

One impact Integral Hydroponics had was to switch many Australians and others over to coco coir substrate and run-to-waste (RTW/DTW) growing. Not a bad thing really as to this day I am yet to find a better medium. Quite simply, coco substrate is fantastic and I highly recommend it.

 

For instance, just one advantage of using coco substrate as a DTW/RTW medium is it is consistently shown in research to outperform other DTW mediums such as rockwool. E.g.

 

[Quote]

 

“Coconut coir, an organic fiber, is readily available in tropical areas as a medium to replace rockwool for vegetable cultivation. We investigated the productivity of cucumber and compared the changes in the nutrient concentrations of coconut coir and rockwool used as growth media. Higher yields (16%) with a higher proportion of marketable fruits were obtained in cucumber plants grown in the coconut coir medium.”1

 

[End Quote]

 

However, there are provisos (warnings) and what has surprised me, since first penning Integral Hydroponics, are the misconceptions that seemingly surround coco substrate among many hydroponic gardeners.

 

Firstly, let me dispel a common myth and say that coco substrate is a hydroponic medium (largely inert) and is very different from soil. One forum actually went so far as to as to have a thread called “coco and soil growing” –implying that the two very different mediums were almost one and the same thing. Let me put things straight. They aren’t. Coco substrate is coco substrate and soil is soil – the two very different products require two very different treatments/approaches to realise optimum yields. Just one example being that optimum pH in soils lies between pH 6.5 – 6.8, while optimum pH in coco is 5.5 – 5.8. Additionally, an optimised soil nutrient will look very different to a coco coir formulation (we’ll talk more about this shortly).

 

OK, so let’s put that aside; coco substrate is a hydroponic medium. Soil is soil. That simple!

 

The next thing that needs to be addressed is that idealised coco nutrient is somewhat different from a standard nutrient due to the organic coco substrate containing often naturally high levels of potassium and (in many cases) sulphates etc. I.e.

 

Analysis of a High Quality Coco Coir Sample

 

All figures refer to ppm (mg/L)

 

Canna Coco Substrate (purchased and tested in the US, September 2011)

 

 

Ref: URAYAMA HISASHI (Nihonkokusaikyoryokuse Tsukubashisho) MATTHEWS LORATO J. (Nootigedacht Adc, Ermelo, Zaf) COETZEE VINAL J. (Dept. Agriculture, Zaf) YAMASHITA TADAAKI (Japan International Cooperation Agency, JPN) (2005) Cucumber Cultivation in Energy-Saving Hydroponic System Using Coconut Coir as Growing Media

 

Coco Substrate Nutrition

 

It’s important to note that CANNA coco is well-treated coir product that is flushed and buffered prior to sale. In simple terms it is a premium product and one that I have previously recommended and continue to recommend for use among growers. In this analysis, sodium chloride is very low, the K is reasonably low at 37ppm, the pH at 6.06 is ideal and the EC (Soluble Salts mmhos/cm) are low. Because of this it is evident that the product is ideally suited for use as a hydroponic substrate. This said, it is also apparent that even a well-flushed and buffered coco substrate contains naturally present levels of potassium and sulphur etc. This needs to be compensated for in the nutrition that is eventually fed to the plant.

 

We have seen that coco substrate contains naturally occurring levels of potassium (K) and therefore a nutrient formulated for coir will have lower potassium (K) levels than a standard nutrient. Other than this we have also seen that coir naturally contains sulphates and therefore a nutrient developed for coir would contain less S than a standard nutrient (or so this should be the case – at least one “hydro” manufacturer has been known to pass off standard nutrients labelled as coco formulations). Other than this potassium competes with magnesium and calcium and therefore both magnesium and calcium levels have been raised in this formulation to compensate for natural potassium levels within the media. Additionally, due to the cation exchange properties of coir, some calcium is immobilized (held) and higher levels of Ca are required in formulation (along with Ca Mg buffering prior to use).

 

I have heard many contend on forums that coco specific nutrients are not required to produce bumper yields in coir. To them, all I can say is all the power to you. If you are getting great results from using non-specific coco nutrients then this, moreso than anything demonstrates the nutritional tolerance of the plant. However, I would also ask, what measurements have you made against a high quality coco specific nutrient versus a standard nutrient and have you run side-by-side trials in order to correctly measure your claims? I.e. have you conducted qualitative, comparative analysis between coco specific and non-coco specific nutrients)?

 

The science…..

 

Research demonstrates that coir immobilizes the Ca ion and other factors come into play when coir is compared to an inert medium (e.g.rockwool). I.e.

 

[Quote]

 

“Coconut coir, an organic fiber, is readily available in tropical areas as a medium to replace rockwool for vegetable cultivation. We investigated the productivity of cucumber and compared the changes in the nutrient concentrations of coconut coir and rockwool used as growth media. Higher yields (16%) with a higher proportion of marketable fruits were obtained in cucumber plants grown in the coconut coir medium. The concentrations of nitrate, potassium, magnesium and phosphorus increased in both media during the growing period. Potassium and phosphorus concentrations in coconut coir were two and eight times higher than those in rockwool. The electrical conductivity, potassium and phosphorus concentrations in coconut coir increased 2.3, 4 and 17 times, respectively compared with those in the nutrient culture solution, while the calcium concentration decreased by one-fifth in the coconut coir medium. The amount of exchangeable calcium was also reduced by more than half in the coconut coir medium through exposure to the nutrient solution. These results suggest that calcium ion was immobilized in coconut coir. The concentrations of the chemical components in cucumber leaf obtained in plants grown in the two media were not affected, despite the existence of significant differences in the nutrient concentrations of the two media.”1

 

[End Quote]

1. Cucumber Cultivation in Energy-Saving Hydroponic System Using Coconut Coir as Growing Media
Author; URAYAMA HISASHI (Nihonkokusaikyoryokuse Tsukubashisho) MATTHEWS LORATO J. (Nootigedacht Adc, Ermelo, Zaf) COETZEE VINAL J. (Dept. Agriculture, Zaf) YAMASHITA TADAAKI (Japan International Cooperation Agency, JPN)

 

Some years ago I had one European company’s formulas for coco and standard bloom analysed. The company makes a single product for coco (one formula used for both grow and bloom) and therefore it is a one size fits all product. Largely however, it is formulated as a bloom product. This was likely due to Dutch growing methodologies where the growth cycle tends to be very short before the light hours are switched down to 12/12 to induce flowerset (i.e. multiples of small plants per square metre). Other than this, you can see our buffer formula (a reverse engineered copy of this company’s formula) contains high degrees of calcium nitrate and magnesium nitrate, meaning a high degree of NO3 Nitrogen and Ca and Mg is present in the coco medium to help facilitate growth in the early veg stages (the extra Ca, N and Mg will be quickly depleted by vigourously growing plants and it is recommended that you use a coco grow formulation if vegging for an extended period of time).

 

OK – so let’s now have a look at the two nutrient analyses (a side by side comparison of Canna’s bloom standard against their coco formulation) and check what the differences are.

 

(Lab analysis conducted in Australia in 2005)

 

 

Total (A+B) NPK of Bloom Standard = 5.58- 1.72- 6.39 Ca= 3.3 Mg = 1.04 S = 1.17

 

Total (A+B) NPK of Coco Formula    = 5.02- 1.6- 2.36   Ca = 5.3 Mg = 1.9   S = 0.79

 

Look closely at the numbers. You will find they are quite different and that the theory (what I have been saying) matches the formulation. It is clear to see that the coco formula contains far less potassium (K) than the company’s standard bloom formula, less sulphate, more calcium, more magnesium and so on. That is, the formulas differ vastly. One is formulated for an inert medium (standard bloom) and one is formulated for a hydroponic medium that contains levels of potassium, phosphorous and other (i.e. coco substrate).

 

Next, let’s look at the elemental ppm in solution (diluted working rate) of these products if used at 2ml/L.

 

Bloom Standard (A+B) @ 2ml/L N= 111.6 P= 34.4 K= 127.8 Ca= 66 Mg= 20.8 S= 23.4 (total ppm 384)

 

Coco (A+B) @ 2ml/L N= 100.4 P= 32 K= 47.2 Ca= 106 Mg= 38 S= 15.8 (total ppm = 339.4)

 

You will note a significant difference in the calcium in solution – 66ppm in the standard bloom versus 106ppm in the Coco; potassium, 127.8ppm in the standard bloom versus 47.2ppm in the coco; magnesium, 20.8ppm in the standard bloom versus 38ppm in the coco and sulphur, 23.4ppm in the standard bloom versus 15.8ppm in the coco.

 

Technicalities/chemistry aside, it’s all very simple. Coir specific nutrients differ significantly to standard nutrients that are formulated for inert medias. This is why I stress that for optimized coco growing a coco specific nutrient should be used throughout grow and bloom.

 




Understanding Cation Exchange Capacity (CEC) and Coir

 

CEC stands for ‘Cation Exchange Capacity’. CEC determines a substrates buffering capacity.  Buffering refers to the resistance to change in pH or nutrient concentration in the substrate.

 

Substrate particles have negatively charged ‘exchange sites’ which attract and loosely-hold cations. Cations such as ammonium NH4+, calcium Ca++, magnesium Mg++ and potassium K+ carry a positive charge. As a result, they are attracted to the negatively-charged exchange sites by electrostatic forces.

 

Where a substrate has high CEC there are a lot of exchange sites and, therefore, large numbers of cations are held at the exchange sites for release into the substrate solution. Conversely, a media with low CEC has very few ‘exchange sites’. Substrates such as peat and coir have moderately high CEC while substrates such as perlite and rockwool have low CEC.

 

A substrate with high CEC can exchange nutrient cations back and forth between the exchange sites and the substrate solution. Therefore, the exchange sites act as a backup “pool” of nutrients to recharge the substrate solution when nutrient levels are low.

 

However, while this sounds quite positive, the CEC exchange sites of coir are naturally loaded with potassium (K) and sodium (Na), with little or no calcium (Ca) or magnesium (Mg).

 

If not buffered correctly, coir can bind Ca and Mg meaning these elements can become unavailable for plant uptake until the coir has been in use for some time and is fully conditioned. Additionally, other elements such as phosphorus (P) and iron (Fe) can become problematic in coir substrates that aren’t buffered correctly. Read more about CEC and coir science here..

 


 

Actually, let me further assert the point now that soil and coco are very different mediums and need to be handled very differently where nutrition is concerned (among other things). Here is an analysis of the same company’s soil flower formula – this analysis was conducted in 2003 in Australia (it may differ from the European formulation but I suspect not). This is a single part formula, whereas our coco formula is a two part A and B set.

 

 

It’s worth pointing out that this analysis is in grams per litre, so to achieve mg/L you simply need to understand that 1000mg (or 1000ppm) equals 1 gram. Therefore 22.0grams Nitrate in the flower formula equals 22,000mg Nitrate. Other than this, elements found in lower concentrations are listed in ppm. 1 ppm equals 1mg/L.

 

This is a fairly simple fertiliser blend which is about 22% solids. EC is high and pH is low because it is made with nitric acid. Relative to other major nutrients, calcium is quite low. As such it is not suited to fertigation (i.e. intermittent drip feed as in run-to-waste systems), but is suitable for less frequent, heavy applications (as you would typically apply in soils).

 

Now compare the soil bloom numbers to the coco formulation – you’ll note that they are extremely different.

You will also note the product contains urea. Urea, CO(NH2)2, doesn’t supply any ammonium nitrogen (NH4 Nitrogen) or nitrate nitrogen (NO3 Nitrogen) and is completely different form of nitrogen to both NH4 N and NO3 N . Urea is widely used in soil applications but is seldomly found in hydroponic formulations.

 

You will note that the soil flower formula contains 35.3 grams of potassium (or elemental K) which equates to 35,300mg/L of potassium (elemental K). Now compare this to our coco formula and note that it contains 23660mg/L when we add the potassium mg/L in part A and B.  Now compare the sulphate levels in the two formulas. In the soil formula there is 68,600mg/L of elemental S, whereas in the coco formula we have 7977 mg/L of S. Now, compare the calcium levels in each formula. In the coco we have 54220mg/L while in the soil formula we 137mg/L.

 

Compare all the numbers if you like and you will find massive differences between a nutrient that has been formulated for soil against one that has been formulated for coco. I hope this clarifies my point that coco and soil are extremely different mediums and require very different treatments. Coco is coco and soil is soil – let’s not get them confused

Optimum Coir Particle Size for Optimum Yields

 

Research has demonstrated that optimum growth rates will be achieved in “medium particle sized” (0.5 – 4mm) coco substrate. The research, conducted on tomato plants and seedlings, measured germination and growth rates in coarse particle (greater than 4mm), medium particle (0.5 – 4mm), fine particles (less than 0.5mm), and raw coco peat (unseived material) with findings that the highest numbers of leaves and growth rates were achieved in medium particle sized coir substrate.

 

[Quote]

 

“Tomato plants grown in coco peat with medium sized particles, showed significantly higher plant heights when compared to tomato plants grown in coco peat with other particle sizes.” 1

 

[End Quote]

 

1. Effect of Particle Size of Coco Peat for Greenhouse Tomatoes: H.K.M.S
Kumarasinghe. Department of Crop Science, Faculty of Agriculture, University of Rahuna

 

Mixing Coir and other Media to Improve Quality

 

Perlite

 

Even the highest quality coco coir may become saturated and compressed over a 10 or so week growing cycle. For this reason, I recommend mixing perlite with coir at a 70 (% coco substrate), 30 (% perlite) rate. This ensures optimum AFP at 30% throughout the crop cycle. I.e. Perlite has approximately 40- 45% AFP and will increase AFP in the coir.

 

Research has shown that the addition of either burnt rice hull or perlite at a ratio of 30/70 (30% burnt rice hull or perlite to 70% coir) improves growth rates in coir.

 

Results of this study indicated that certain chemical and physical properties of cocopeat can be improved through incorporation of burnt rice hull or perlite. The positive effects of burnt rice hull or perlite were seen in the elevation of nutrient availability (as indicated by higher EC), increased bulk density, air-filled porosity, available water and wettability. Improvement in chemical and physical properties following incorporation of burnt rice hull or perlite into cocopeat was reflected in a better plant growth.1 See table below that demonstrates increased AFP of coir when 30% perlite or 30% burnt rice hull is added to substrate.

 

see reference 2

 

Each particle of perlite consists of tiny air cells that provide for a large surface area. Because of the shape of perlite, large air gaps form between the particles. This means there is plenty of oxygen available to the root system.


Perlite doesn’t compact and because of this maintains an ideal balance of oxygen and water (oxygen moisture ratio).

 

Perlite is very tolerant to overwatering which makes it very forgiving medium. Because of its nature, perlite allows excess water to drain off and provides an air ratio of approximately 40- 45%.


Perlite, like coco, has thermal insulation qualities, which provides the root zone with a high degree of security against heat.

 

Perlite is a very cost effective medium. It is about half the price of expanded clay.

 

Lab Analysis: Comparison of Perlite and Coco Samples

 

Perlite


Air Porosity: 40%
CEC: 5.0
Water Holding: 28.9

 

Coco (6mm particle size)


Air Porosity: 20%
CEC: approx 63.1
Water Holding: 66.5


Buffered Coco (Medium Particle Size Sample)


Particle Sizes: 
MATERIAL > 2mm % 7.5
MATERIAL 1.00 – 2.00 mm % 25
MATERIAL 0.85 – 1.00 mm % 27.5
MATERIAL 0.30 – 0.85 mm % 15
MATERIAL 0.075 – 0.30 mm % 22.5
MATERIAL < 0.075mm % 2.5
CATION EXCHANGE CAPACITY 56.69
Water Holding: 51
Air Porosity: 30%

 

Re Air Porosity Measurements

 

There are two methods that are commonly used for measuring Air Filled Porosity (AFP) in the coir. These are:

 

The European EN-method: Loose coir (no compression) is saturated with water and allowed free drainage for 24hrs. AFP is then measured. A quality buffered product such as Atami coir measures at approximately 35 – 40% AFP under this method.

 

The Dutch BLGG method: Coir is slightly compressed in a container and saturated with water where it is then allowed free drainage for 24hrs. Atami buffered coir measures at 20 – 25% AFP under this method.

 

Note when using perlite: Also pre rinse/wash the perlite prior to mixing it with the coco. Perlite is typically alkaloid and a fine dust will be removed in washing.

 

1 & 2. Chemical and Physical Characteristics of Cocopeat-Based Media Mixtures and Their Effects on the Growth and Development of Celosia cristata Yahya Awang, Anieza Shazmi Shaharom, Rosli B. Mohamad and Ahmad Selamat Department of Crop Science, Faculty of Agriculture, University Putra Malaysia

 

 

Clay Balls/Expanded Clay (e.g. Hydroton) and Coco Substrate

 

I’ve noticed on internet forums that many growers speak of using expanded clay instead of perlite when working with coco substrate and RTW growing.

 

Other than this, many growers seemingly use expanded clay at the base of the pots to allow for “better drainage” (not a bad idea, although I have never found drainage to be a problem). That is, some growers line the base of their pots with expanded clay to perhaps two to three inches and then fill the pots with a mixture of coco substrate and expanded clay.

 

I personally can’t see a problem with using expanded clay with coco substrate other than perlite has a higher air capacity than expanded clay (45% versus approx 30%). Other than this expanded clay offers the roots less security than perlite and is an effective conductor of heat.

 

Bottom line: Perlite mixed with coco at 30/70 ratio will provide better outcomes than a coco coir, expanded clay mix.

 

High Quality Flushed and Buffered Coir Products v. Brick Coco

 

A Quick Warning – Coco and Sodium Chloride


OK – so the high quality buffered products tend to cost more. Those cheap compressed blocks that you can buy from gardening centres and hydroponic stores are just as good as premium grade buffered coco coir – or at least this is what is asserted by some!

 

However,  compressed products can also be substandard.

 

E.g. Lab Analysis of a Compressed Coco Product

 

 

Take a close look at the elemental analysis of our coco substrate product. I would point out that this was a compressed product from Holland (originally deriving from Sri Lanka) which was tested after questions were raised as to why the product was seemingly killing plants.

 

You will note extreme levels of sodium and chloride or sodium chloride (NaCl or common salt). That is 2022ppm of sodium and 3498ppm of chloride. That is 2022mg (20.22grams) of sodium and 3498mg (34.98grams) of chloride Given that even 200 -300ppm of NaCl is dangerously high to many plants, the sodium chloride levels in this product were extreme and it resulted in disaster.

 

So another important factor that needs to be addressed – untreated coco coir can contain high levels of sodium chloride (common table salt). Try to remember that coconut palms grow well in areas of high salinity. This means they uptake a lot of salt from their environment. Plants that are salt tolerant are able to uptake salt and then displace it into areas of the plant where it does the least harm. Seemingly, much of the salt is displaced into the coir of the coconut palm (the very thing we use as a hydroponic medium). Factors that will influence the NaCl levels in any coir product include the treatment it has received prior to sale and how far inland the coconut palms are grown (the further inland the less salinity/salt in the soil/sand and hence the less salt that is uptaken by the coconut palm).

 

Other than this you will note 3700ppm of Potassium and 1978ppm of sulphate. This tells us that there are sometimes extreme levels of potassium and sulphate that are naturally present in just some of the untreated coir products.

 

Signs of toxicity (high levels of NaCl in coir substrate)

 

  • Slow/stunted growth
  • Unhealthy plants
  • Yellowing
  • Burning
  • Rusting on edges of leaves
  • Rust spots on leaves

 

Flushing and Buffering Compressed Coir Blocks

 

Let’s now talk about how to use (prep) a cheap compressed or uncompressed (non buffered) product that you buy through garden centres or hydroponic stores. That is, how to buffer the compressed product correctly to ensure a reasonably decent product for use as a growing medium.

 

It’s important to note that some coir products available through garden centres etc may be sold as soils/potting mixes with NPK added – avoid these products – they are not developed for hydroponics. Besides this, the compressed blocks are cheaper and you’re now about to learn how to turn these into a buffered hydroponic coir substrate.

 

Here’s our buffer formula used to pre-treat and hydrate compressed coir blocks.

 

Coco Substrate Buffer

 

(Used for preparing non-buffered coco substrates such as compressed coco blocks)

 

Calcium Nitrate                       290 g/l
Magnesium Nitrate                  280 g/l
Magnesium Sulphate              10 g/l
Ferric EDTA                               2 g/l

 

Make 1L by beginning with 750ml of RO (demineralised) water.  Heat the water to 40 0C (104 0F) before mixing. Add ingredients one at a time, dissolving each ingredient before adding the next. When all ingredients have been added, top up to 1000ml (1L) with RO water.

 

What I recommend that you do is hydrate the coir blocks in mains (tap) water. That is, fill a bucket or tub with mains water.  Measure the EC of the mains water before adding the compressed coir block/s. Let’s say it’s EC 1.0 for arguments sake. Add the compressed coir block and allow it to expand. Stir the water and coco substrate around and then measure the EC again. You’ll no doubt find the EC is now much higher. OK, now run mains water through the coir (you may find a bucket with holes and mesh at the base helps here). Run the mains water through (flush) the coir until the water that has passed through the coir (runoff) is no more than EC 1.0 – 1.2. I.e. Original mains water EC ideally matches that of the runoff EC.

 

Now fill up a bucket with demineralised (RO) water and dilute the buffer concentrate to 1.4 EC and pH adjust to 6.0. Place the hydrated/expanded and water flushed coir into the diluted buffer solution and leave to soak for at least one hour.

 

After one hour or more, take out the now buffered coir and squeeze out the excess fluids so the coco substrate is not saturated/water logged. You may find drying it in the sun for a while helps.

 

Ready to go – you now have a buffered coir product at a fraction of the cost that you would pay for similar products through stores. I’d also recommend that you mix the coir with perlite. 70% coir to 30% perlite when using it as a RTW/DTW medium.

 

Tip: Many of the compressed coco blocks that are purchased through gardening centres are (when uncompressed) coco powder. If this is the case, look for varying grades of coco substrate, working from fine to larger fibres and mix them into a single product to increase air porosity within the media. The ideal coir particle size is 0.5 – 4mm. See following.

 

pH measurements in Coco Coir

 

Coco coir buffers pH in the range of 5.5 – 7. However bacterial activity and nutrient quality can have an impact on pH stability within the media.

 

Another misconception I have commonly encountered is that by measuring the run off (waste) in coir it is possible to measure the pH of the medium. Let’s quickly dispel with this myth. Coir media will retain some elements and release others (a process of preferential retention of cations) based on the uptake needs of plants and the prevailing conditions of/within the media.

Because of this, measuring the run off (waste) will not reflect the pH within the coir medium (i.e. the rhizosphere environment of the plants).

 

The correct way to measure pH, in coco substrate, is to take samples of the media from around the root zone. These samples are then added to distilled water at a 5:1 ratio (5 parts distilled water to 1 part media), then vigorously shaken or blended and tested with a pH meter. This method will provide you with the correct pH within the coir media (rhizosphere) environment.

 

An entire article on coir science that goes into detail on CEC, Salt Buildup, pH and EC testing etc can be found here…

If you really want to know your stuff about coir, I strongly recommend that you read this article.

 

Feed Regime

 

In Integral Hydroponics Edition 1 to 4, I recommended multiples of smaller feeds allowing for between 10 – 30 per cent run off. Technically, at least from a agricultural (science) perspective this is the recommended way of feeding.

 

If using RO (demineralised) water I would recommend a 10-20% run off (waste) regime.

 

If using mains (tap) water, I would recommend run off (waste) be maintained at 30 percent due to naturally present salts that are often found in tap water supplies. Elements such iron (Fe), magnesium (Mg), calcium (Ca) and sodium (Na) and chloride (Cl) which combined form common salt (NaCl). Sodium and Chloride normally occur together and are not taken up to any degree by most plants, especially sodium; therefore, they tend to accumulate if present in significant amounts.

 

In some cases tap water supplies can contain high EC/ppm levels of these salts (ions) and this can detrimentally affect the growing medium. Therefore, in order to circumvent any problems that can occur as a result of this, I recommend a higher waste percentage if using mains water than if you were growing with RO or rain water.

 

I should also add some information now, regarding feed regimes in coco substrate.

 

Since writing Integral Hydroponics (originally published in 2002) I have seen growers using all manner of feeding techniques and achieving extremely good results. One friend – a long time and very advanced grower – who had been using a wide channelled NFT system switched to coco coir and contrary to my advice began hand watering. I was somewhat perplexed by why he would go this way but I’ve always preached KISS (Keep It Simple Stupid) and was intrigued by his methods. For the next 10 or so weeks I watched closely as my friend Feral saturated his pots full of coir twice daily (during the lights on period) with a resultant approx 50 per cent run off on each feed.

 

“Mate, you’re over watering” I contended,” the medium is too saturated and you’re reducing the natural air porosity of the medium.  (A quality coco substrate product will possess approximately 30 per cent air porosity, which is ideal for rhizosphere health).

 

“Yeah, but they look great and they’re growing faster than anything I’ve ever grown before”, he responded. To this I couldn’t argue; indeed, the plants were as healthy as any I’d seen and were growing at a rapid rate.

 

On his first grow he realised a 30 – 35 per cent increase in yield to what he had been achieving through his much touted (bells and whistles) wide channel NFT system.  Of course, at this point he was sold and began switching all of his friends to coir substrate RTW growing (after years of promoting the wide channelled NFT system via internet forums to all who would listen).

 

The moral of the story is this. There are ideals where agricultural (scientific) principles are concerned. However, what I have learned (gained) from Feral and others is that coco substrate tends to be so forgiving, that whether you feed multiples of small feeds with 10 – 30 per cent waste (methodology correct)  or whether the medium is hand watered and therefore more saturated, you will achieve great results.

 

Coco Substrate and Sciaradae (Fungus Gnat, Shore Fly)

Because coco substrate is organic it slowly decomposes in its wet state. This causes the release of nitrates as part of the decomposition process. There’s not much wrong with this as long as the nitrate release is minimal (which it is). However, this nitrate release is what attracts Sciaradae (fungus gnat). Sciaradae are commonly found in organic composting material. Therefore, coco substrate can be a highly effective attractive media for Sciaradae.

 

Sciaradae, shore flies or fungus gnats are often present in conjunction with pythium. Fungus gnats feed on rotting vegetation and other decomposing organic material. It is not certain whether fungus gnats are drawn to crops that are suffering pythium because of the presence of decomposing organic material or whether fungus gnat is responsible for introducing the pythium. It is more likely that the fungus gnats are attracted to rotting vegetation that is inhabited by pythium fungi (oospores). The gnat larvae (1-2mm white maggots with black heads) can live on a diet of pythium oospores before some of them mature into the flying stage (adults) and carry fungi to other crops. This means the presence of the fungus gnat could be a precursor to a pythium outbreak in your crop.

 

Other than this, Sciaradae larvae are laid by the adults in the growing medium and their food source largely consists of the roots of the plants and decomposing material.

 

Adult Sciaradae resemble tiny fruit flies. When they are put under a magnifier their wings can be seen to have, what look like, accentuated veins. Sciaridae have a life cycle of egg, larvae, puparium, and adult. While the adult flies will only live a few days, one female fly can lay as many as 200 eggs. The lifecycle from egg to adult can be estimated at 3-4 weeks. For this reason infestations occur at a rapid rate.

 

Sciaridae eggs are laid around the soil/media surface. These hatch into glossy, legless larvae with black heads. The larvae are equipped with a sharp pair of mandibles, which are used for sawing and rasping into the soft stems and roots of the plants.

 

Controlling Sciaradae

 

Pesticides: I have found that after using numerous approaches and products (biological and pesticide) the Permethrin based products (Coopex, Axe etc) are the most effective treatment for totally eradicating Sciaradae from the crop. Permethrin is non systemic and and degradates (neutralises) quickly which makes it ideal as it is not up taken by the plant in any way.

 

The product I typically work with is Coopex WP 250g/kg powder which comes in 25gram sachets. Coopex is manufactured by Bayer and is widely available in most countries. Mix one sachet to 10 litres, hand water (drench) the media and leave for an hour. After this, flush with pH adjusted nutrient and you are ready to go.

 

Yellow sticky traps hung at media and plany canopy height will trap the adult Sciaradae. This will help reduce numbers. More importantly it will allow you to monitor whether Sciaridae are present in the growing environment.

 

Tip (About Sciaradae)


Look out for:

Signs of the pest through the use of yellow sticky traps

Deformed leaves and generally unwell plants can indicate an infestation of Sciaradae

 

A lot more information about fungus gnat/sciaridae and coir can be found here 

 

Recycling the Media

 

Coco substrate can be used in more than one crop cycle if it is prepared correctly prior to reuse.

 

The key here is in cleaning the media of dead root material (cellulose) and priming it with a buffer before reuse.

 

I have noticed on forums that many people speak of using Zyme (e.g. Cannazyme, Sensizyme) products for breaking down the dead root material. This is an area of concern due to the fact that while fungal cellulose enzymes are definitely effective at breaking down cellulose (after all, this is what they do in nature) the products sold through the hydro industry possibly/probably are inert. I.e. Devoid of enzymes.

 

There are serious question marks over the shelf life of liquid enzyme products. That’s not to say that enzymes are a bad thing -without a doubt they have a place in hydroponics/agriculture and can be potentially beneficial to plant health. However, as with friendly bacteria, the sale of these products through the “hydro” industry is, often, greatly over simplified (talked up and hyped). That is, the enzymes are contained in a liquid state and because of this they may or may not be present/active when they are purchased off the shelf. Other than this, enzymes aren’t so dissimilar to bacteria in that they need a complimentary environment in which to remain stable and work. However, by their very nature enzymes are unstable and herein lies the problem. I.e. If I make a liquid concentrate and then put it on a shelf for months at a time will there be enzymes present or not when that product is purchased? Probably not….

 

One producer who sells a Zyme product claims they have tested their competitors Zyme formulas and found that they were (to quote) “junk”. They go onto say, “Enzymes have a shelf life. They can expire in their bottles.” Other than this they claim to have purchased five different companies formulas (from several locations), including their own, and after testing their competitors’ products they were found to be “inert, meaning there was no biological activity left in them.” Of course, their formula, when tested, came through with flying colours.

Back to reality and the science – let’s avoid the scam factor that is too often proliferated by a few to so many.

 

So, what is a reliable/effective means of recycling the media?

 

Trichoderma Harzianum (T.harzianum)

 

A lot of research has been done with a mould called Trichoderma harzianum with very positive findings. Trichoderma harzianum is a friendly mould that colonises the rhizosphere and competes with other organisms.

 

Trichoderma is parasitic to other moulds such as pythium, fusarium and phytopthora. That is, Trichoderma protects the plants from these organisms, all of which are capable of destroying your crop.

 

Trichoderma enhances plant growth due to its ability to produce beneficial enzyme complexes. Trichoderma can also survive for long periods in a host, and needs only minimal carbon levels to ensure its subsistence. Trichoderma also stimulates root growth while breaking down cellulose (dead root matter etc) and therefore is an extremely effective and reliable way to treat media for reuse.

 

Coco substrate, more so than any other hydroponic medium, provides an ideal environment for friendly moulds and friendly bacteria.

 

To recycle the media effectively, remove as much dead root matter as you can by first cleaning, washing and sieving the media and then apply a treatment of T.harzianum to the coco substrate. Maintain its use for several weeks (better yet – throughout the entire crop cycle) and watch your plants grow.

 

Which brings us to our next point – the use of ‘friendlies’ in coco substrate.

 

Understanding Friendly Bacteria

 

This is an area which is largely misunderstood by many indoor growers so I thought I’d expand on the science of friendly bacteria in hydroponics.

 

Friendly bacteria protect the plant from water born pathogens such as pythium and fusarium. Other than this, they help in nutrient uptake and produce plant growth promoting substances. They can also protect plant surfaces from attacks by pathogenic microbes through direct competitive effects and production of anti pathogenic compounds. To really know your stuff there is a comprehensive article on beneficial bacteria and fungi in hydroponics here……

 

Read more about coir science here….