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How sustainable is coir?

Coir is a popular alternative to peat in potting composts and growing media, but information on its sustainability and properties can be elusive. We pose some of the big questions around coir to Responsible Sourcing Scheme Chair Steve Harper

Coir is a by-product of the coconut industry. It is made from coconut husks, the fibrous outer shell that would otherwise become a waste product when the inside of the coconut is processed into coconut oil and other products. UK coir is imported mainly from India and Sri Lanka.

As a common substitute for peat in potting composts and professional growing media, coir retains water well and has a light texture that allows air into the mix to keep roots healthy. However, information on how well coir retains nutrients, and the sustainability and ethics of its production, is less readily available.

Steve Harper, Chair of the Responsible Sourcing Scheme for growing media – which assesses the environmental impact of each raw material – and CEO of Southern Trident, a growing media manufacturer specialising in coir-based peat-free composts, answers the questions he most commonly hears on coir.

 

© Steve Harper
Shelled coconuts, showing the fibrous husk that is used re-purposed into coir
Water use in production

There’s a lot of criticism around the water used in producing coir, especially the washing stage, and then in expanding it when it reaches the UK. Can you address how water is used and whether it’s sustainable?

“Water use by the coir industry is highly monitored in India,” says Steve Harper. “All water is controlled by the State, unlike private water companies in the UK. There are three separate designations of water in India – human consumption, agriculture and coir industry. The coir industry water is defined as commercial water and is switched off as soon as there is any risk to supply.

“Waste water from our factory is put back onto the plantations, reducing the need to water them. This has been done for decades with no issue, and any build-up in salt levels is diluted during the monsoons.

“It is monsoon season in these areas for seven months of the year, during which time too much water becomes a bigger problem.

“Coir is transported in a dry form to reduce the weight, and then needs to be rehydrated (expanded) to be made into growing media. Though there are sometimes claims that this uses a lot of water, we use captured rainwater when expanding the coir at our UK factory.”


© Steve Harper
Coir blocks being stored before shipping in this compact, dehydrated form
Chemical use in washing 

Concerns have been raised over the chemicals used in washing coir, and potential water pollution as a result. Are you able to provide clarity on what chemicals are used for washing, and any steps that are taken to prevent contamination of water courses?

For washed coir (the vast majority of coir), plain water is used. For buffered coir (used by a few growers), calcium nitrate is added, but this is a tiny minority compared to washed.

The washing water is either captured and treated so that it can leave the site without causing pollution, or used for example for watering plantations, as the trees are very tolerant of salt water. Other methods for treating the water are sedimentation tanks, filtration systems, closed loop systems and evaporation ponds.


Levels of salts

Coir is known to have high levels of natural salts (causing what growers refer to as a high electrical conductivity, EC, which can affect nutrient uptake by plants). How does this affect the usability of coir, and what measures are taken to make it suitable for horticulture?

“This is where the washing of the coir at source comes in, to remove the salts,” says Steve Harper. “Where there is no need for the electrical conductivity (EC) to be lowered, we use unwashed coir (mainly non-horticultural uses – coir is also used to make products such as doormats and brushes).

“Specifications for washed coir state that the EC is reduced to less than 500 microsiemens, but on average, this is probably more like 300 or less.

“‘Buffered coir’ can also be produced if required, which uses calcium nitrate to adjust the concentrations of salts. In most cases though, plants don’t need the coir to be buffered. It is only really used where growers want to be very specific about the nutrient uptake for salt-sensitive plants.”
 

Water retention

Coir is often promoted for its water retention properties. Can you explain why it’s effective and how it compares to other growing media or compost ingredients?

“Peat may be great at holding water, but coir comes a close second, holding 10 times its dry weight. Growers and gardeners sometimes complain that peat-free growing media dries out too quickly, but that’s partly because other common alternatives to peat are less water-retentive – composted bark can only hold about three times its own weight, and wood fibre only about two times.
 
“We also need to consider the air-filled porosity (AFP) of the ingredient, which determines how much air the mix is able to retain alongside water to ensure healthy roots. Coir AFP ranges from 10-20%, whereas peat is 5-15%, so considering this and the water-holding capacity, coir becomes a better prospect.

“Over time, peat also starts to compact, reducing aeration, whereas coir, because of its high lignin content (a compound found in plant cell walls), is stable over a much longer period of time. In the soft fruit market, blueberries are grown in coir for up to 10 years, which shows its longevity.”


Cuttings require a mix that has good water retention but is also well aerated. Shown here in a coir-based compost.
Performance 

Are there specific plant groups or scenarios where coir performs exceptionally well or poorly?

“Coir generally performs well with most plants. Unless it’s adequately washed to remove salts, you may have issues with carnivorous plants, as they are particularly sensitive to residual salts.
 
“The pH of coir can be a bit too high for acid-loving ericaceous plants, with a pH 5.5-6.2 on its own, but when blended with other materials of a lower pH, it works well. Our ericaceous mix for gardeners blends coir with pine bark, which we have found to be effective.”


Carbon footprint

What is the carbon footprint of coir production, and how does it compare to other substrates such as peat?

“The carbon footprint is lower than most people assume. Since it’s a by-product of the coconut food industry, historically, it was a waste material. This meant it piled up, went anaerobic and produced methane, which is 27 times more potent as a greenhouse gas than carbon dioxide.

“Coir is also highly renewable. Coconut plantations produce several crops a year, unlike peat, which takes thousands of years to form just a metre’s depth. Coir is also frequently re-used, such as in the soft fruit industry, thereby reducing its carbon footprint further.

“Coir is transported in a compressed form that makes it highly efficient to ship. Shipping coir from the port of Tutti Corin in India to Liverpool produces 40% less carbon emissions than transporting composted bark from Scotland to Liverpool. This is because bark travels by road, the most polluting form of transport, and the lorry can only hold 60-65m3, whereas a shipping container holds over 350m3 and is transported with up to 14,000 other containers on the same vessel.”


Energy use

How energy-intensive is coir production, and are there efforts to make the process more sustainable?

“Coir processing in India is mainly in Tamil Nadu, where copious hours of sun per day dry the coir energy-free. This is also an area that is rapidly growing its renewable energy usage, such as through wind power. I believe renewable energy use here currently stands at around 57% and is rising.”


© Steve Harper
Coir drying in the sun near a coconut plantation in India
Worker conditions

Ethical concerns have been raised about the working conditions in coir-producing regions like India. What steps are being taken to ensure fair wages and safe environments for workers?

“Our factory is registered with Sedex (Supplier Ethical Data Exchange) and scores well. We are about to go through a SMETA (Sedex Members Ethical Trade Audit) to validate those results. This is a global audit that assesses a company’s ethical and responsible business practices.

“As part of the Responsible Sourcing Scheme, we are looking at getting an auditor to audit the factories. These audits will have a clear remit to look at the social compliance of workers.

“It is important to note that the coir industry employs around 700,000 in India alone, mainly in rural areas where employment opportunities are lower, and mostly in states where wages compare reasonably favourably against other areas.”


Wider environmental concerns

How does coir production affect local ecosystems in producing countries? Are there any initiatives to mitigate negative impacts?

“One of the most important things we have done as a company is to go Carbon Neutral. As part of that, we invest in programmes in India to compost coconut waste that isn’t part of the coir industry – mainly from the food industry.

This has two benefits – it reduces the risk of methane release through material going anaerobic, and the resulting compost can be spread on land in India to improve its soil organic matter content. On average, soil organic carbon levels in India are 0.2%-0.5%, whereas a soil that is considered healthy would usually fall between 3% and 6%.

Some people are concerned that deforestation is taking place to plant coconut plantations. From a study conducted by the Sustainable Coconut Partnership, it would appear that only about 0.3% of mapped forests across eight coconut-growing countries, including India, the Philippines and Indonesia, have been lost to coconut plantations.’’

All views expressed within the Q&A are those of Steve Harper, Chair of the Responsible Sourcing Scheme and CEO of Southern Trident. You can find out more about the RHS work around peat-free here and more on common peat alternatives here.
 
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