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Why Coco and Run to Waste

The key to optimised yields is an optimised environment (light, temp, RH, CO2 availability etc) and optimised nutrition. Get all of the factors right, all of the time, and you will reap optimum yields.

In order to create the best environment for your plants there are several things that need to be considered. These are – airflow, light, CO2 levels, Relative Humidity (RH), and temperature (ambient air temp and root zone).

Other than these factors you also need to consider:


Optimised nutrition (along with an optimised environment) leads to optimum growth rates (hence final yields). For this reason it is important that

  1. You provide a sound nutritional program to the plants through the use of a well balanced nutrient and additive program
  2. That the nutrient is maintained at the correct temperature to ensure adequate levels of oxygen are available to the roots of the plant
  3. That the nutrient is maintained at optimum elemental levels and is not allowed to become depleted and/or imbalanced
  4. That the nutrient is maintained at the correct pH to ensure optimum uptake (bioavailability) of the mineral elements required for plant growth
  5. That the nutrient is maintained at the correct EC to ensure that viable amounts of food are readily available to the plants

Growing System

While there are many growing systems on the market today they can all be categorised as run-to-waste or recycling systems

Recycling Systems

In recycling systems (e.g. airoponics, NFT) the nutrient is delivered to the plants and then returned to the reservoir. This nutrient is then delivered to the plants again and again and again and over time this can lead to it becoming imbalanced and depleted due to the plants up taking some elements at higher rates than others. Particularly where plants with high uptake needs are concerned this situation/problem can become more pronounced. While it is possible to run these systems extremely well they require regular maintenance and dumping (of the nutrient) to ensure the plants are receiving an optimised (balanced) nutritional program.

I was recently reading the book Mc Mafia (Seriously Organised Crime) and came upon a quote that put me into belly fits of laughter.

A Jim character from BC was quoted by the author as stating that with the evolution of airoponics and CO2 in indoor growing, BC growers were getting up to 70 percent increase in yields to that which they were several years before. What he actually meant by this I’m not really sure but in making such a statement he was clearly (among other things) delusional. Not to worry – it did sound impressive….

Technically speaking, based on the science/research, the correct use of CO2 (at 1,500 – 1,800ppm atmospheric CO2) should increase yields by 10 – 30% while cutting down crop cycle times by 10-30%. For this reason, realistically, we are talking, on average, perhaps 30 % overall increase in yields during the course of a year. This makes CO2 a great thing and when handled correctly it will definitely pay off. On this front our friend Jim from BC had got it right. CO2 is the bomb and big yields really do come in bottles!!!!

However, the use of airoponics over other growing systems/methods (when they are handled correctly) is unlikely to result in yield increases. Let me explain the principles. That is, the science of plant growth and air porosity within the media.

Put simply a plant can only use so much oxygen that is available to the rhizosphere (roots). This figure tends to be asserted at approximately 25 -30% oxygen availability (air porosity). Give a plant more oxygen to the roots than this and it can’t use it – much as the same way that a plant can only use so much atmospheric CO2 (i.e. when enriching a growroom with CO2 you eventually reach a limit set by how fast the machinery of photosynthesis -the chloroplast- can tick over and any additional CO2 you inject into the air, at this point, will go to waste). Put simply (at least according to the science), airoponics offers no real benefits over other growing systems and, in fact, I would argue is less effective than run-to-waste methods of growing. This is because airoponics recycles nutrient, which over time becomes depleted and suffers pH fluctuations, while run-to-waste methodology provides fresh (new) feed/nutrient time after time after time. This offers distinct benefits over any form of recycling system.


Run-to-waste is the term used for a hydroponics system where nutrients are not recycled. Run-to-waste systems (typically) use an inert medium that has similar fluid retention rates to that of soil. That is, run-to-waste mediums retain a high degree of moisture for an extended period of time. Because of this, feeds are smaller and not as frequent as feeds in a recycling system. In the run-to-waste system plants are given a regulated dose of water and nutrient at such a rate that a given amount of the water/nutrient drains from the medium (as waste). The excess water and nutrient is then allowed to drain into some form of catchment away from the reservoir.

Because the nutrients are not recycled there are some distinct advantages associated with run-to-waste systems.


  • No nutrient exhaustion/depletion as the plant receives fresh nutrient at every feed
  • pH stability over and above that of a recycling system
  • EC stability (in nutrient tank) over and above that of recycling systems
  • Nutrient less prone to bacteria/pathogen build up
  • Nutrient less prone to sodium chloride (NaCl) build up where mains water is used
  • Less maintenance

The run-to-waste system is ideal for larger plants with high uptake needs. Because of the density and fluid retention rates of the medium, the run-to-waste system has security features unmatched by other systems.

  • Roots are well insulated from heat
  • Moisture retention in medium will last for days, giving the plant/s protection from pump and pump timer failures. These are very attractive features for experienced growers who know that heat and equipment failures can very easily result in crop loss.

Coco Substrate and Run-To-Waste Growing

Coco substrate has become the Australian grower’s choice since, perhaps, as early as 2000 – 2002. This speaks volumes about this medium….Simply, it is the best!

Coco provides excellent insulation. This means that coco isn’t prone to overheating, due to excessive ambient air temperatures, as many other mediums (making it ideal for warm geographic zones). This is because water tends to make its way into the lower regions of the coco coir, leaving the top layer relatively drier. Because of this, heat needs to penetrate a drier top layer of coco coir before reaching the watered areas of the media. As water is a great conductor of energy (in the form of heat) the lower wet area being protected by a drier surface helps keep the lower areas of the media, where the bulk of the root mass is found, cooler. As media temperature and oxygen levels (air porosity) are interrelated (the warmer the media the less oxygen) this insulation plays an important role in promoting root health and vigour.

Compare coco coir to rockwool, another run-to-waste media. There are some significant differences in moisture distribution and media insulation qualities. Rockwool tends to become excessively saturated. Water, thus, distributes evenly from the top to bottom, leaving the rockwool, typically very damp. This means that heat can travel throughout the media (dry rockwool is an excellent insulator; it is simply the water that conducts heat). When the air temperature is excessively warm so too is the media. Depending on the extent of this problem (too warm – not enough oxygen), oxygen availability to the root zone can become dangerously low.

Coco substrate contains natural rooting compounds, in the form of potassium (electrolytes) and phosphorous (enzyme function and sugar production). Both potassium and phosphorous stimulate root growth and development.

Coco coir has excellent air filled “porosity” – the term used for the levels of oxygen availability in the media. This is due to the large surface area of coco particles. As oxygen plays an all-important role in respiration (roots pumping nutrient to the plant) this factor further promotes root and (hence) plant health.

What these factors add up to is that coco substrate provides a sound environment for the plant’s root zone. This factor should not be underestimated because healthy roots (along with other factors) invariably lead to a healthy plant and healthy yields.

Coco Nutrients

Because coco substrate contains high levels of potassium, some phosphorous and some sulfates a nutrient for the substrate needs to be formulated with this in mind. That is, coco is not truly an inert medium (unlike rockwool, perlite, expanded clay etc) and therefore coco substrate nutrients differ somewhat from standard nutrients. That is, a quality coco nutrient should have lower levels of potassium, phosphorous and sulfates. Other than this, because of the cation exchange properties of the substrate a good coco formula should contain higher levels of calcium, nitrate and magnesium.

We recommend CANNA or House and Garden coco nutrients for providing an idealised nutritional program. Both companies have done extensive research in the area of the coco substrate (crop specific growing) and have developed extremely good products as a result.

Feed Regime

Where working with RO (demineralised) water we recommend a 10-20% run off (waste) feed regime.

Where working with mains water we recommend a 30% run off regime to cater for the NaCl (sodium chloride) and other elements that are naturally present in mains water supplies. Sodium (Na) and chloride (Cl) are the constituents of common salt. These normally occur together (i.e. sodium chloride = NaCl) and are not taken up to any degree by most plants, especially sodium. Therefore, they tend to accumulate if present in significant amounts. More runoff helps to limit the build up of problematic elements within the media.

Lower EC requirements than standard media

Coir retains nutrient salts due to its cation exchange qualities. Because of this less nutrient (EC) is required. I.e.

Nutrient requirements in standard media such as Perlite and Expanded Clay

Grow: 1.8

Grow/Bloom: 2.2

Bloom: 2.8

In Coir:

Grow: 1.0 (RO) – 1.4 (mains)

Grow/Bloom: 1.8 (RO) – 2.0 (mains)

Bloom: 2.0 (RO) – 2.4 (mains)

Coco Substrate Products – they aren’t all equal

If coco substrate isn’t treated correctly prior to use it can be less than ideal as a growing medium.

Coco substrate comes from the coconut palm. Coconut palms grow extremely well in areas of high salinity (salt). This makes the coconut palm a very salt tolerant plant. The problem here is that salt tolerant plants are able to uptake salt and displace it into areas of the plant where it does the least harm. In the case of the coconut palm it displaces salt into the coir (husk) and this is exactly what is being used as a hydroponic growing medium.

This (and other factors) makes the correct treatment/preparation of the media, prior to use, extremely important.

For instance, coir needs to be flushed and buffered with calcium and magnesium to offset the NaCl levels, to compensate for natural potassium and sulphate levels and to charge (prepare) the medium with the right ions to facilitate adequate cation exchange capacity (CEC) within the medium.

For this reason we recommend the use of premium quality buffered products such as CANNA Coco.

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