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Why Coco & Run to Waste?

Tara | January 4, 2022
Coco Coir

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).

Beyond these factors you also need to consider:

Nutrition

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 solution is 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 either run-to-waste or recycling systems:

Recycling Systems

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

Run-to-Waste

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.

Advantages
  • 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 the early 2000s. This speaks volumes about this medium….simply, it is the best!

Coco provides excellent insulation. This means that coco isn’t as 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 dry. As a result, heat needs to penetrate the 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.

Compared to rockwool and another run-to-waste media, coco has significant differences in moisture distribution and media insulation qualities. Rockwool tends to become excessively saturated. As a result, water 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, 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. Root health should never be underestimated because healthy roots 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 BAC, CANNA or House and Garden coco nutrients for providing an ideal nutritional program. Each company has performed 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
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