What Is Coir and Where Does It Come From?
Coir is commonly pronounced “core” in the United States and “kwar” in France. In Spanish, it’s called “coco de fibra.” No matter how you pronounce it, coir is a byproduct of the coconut industry. While coconuts are primarily farmed for their white “meat,” which is used in various food products, growers have found uses for the coconut husks as well.
Hugh has visited India and Sri Lanka and seen coconut husk processing first-hand. He says it started as a cottage industry — something that families did. Once the husks were separated from the nuts, the husks were tossed into a pile or a pond so rainwater would help the fibers separate more easily.
Using knives or other tools, they break the husks into smaller parts. While rubbing the fibers of the husks, granular material — the coir — falls out.
The family that collected the coir would then send it to a factory where it was compressed into pellets or blocks. As the industry has grown, it’s become typical for whole husks to be delivered to factories, where the husks are put through a chipper. Those chips are used in hydroponic growing. In fact, Hugh says it was hydroponics in Europe that turned coir production into a true industry.
The granular coir or chipped coir, compressed into pellets or blocks, are then sent on pallets to the United States and Europe.
Coconuts are grown all over the tropics but there was historically no demand for these byproducts, and the husks went to waste. Today, coir has grown so much in popularity for horticulture that in Central America and Southeast Asia it is no longer a byproduct of farming coconuts but the product itself in many cases.
Supply chain issues have made coir more expensive in the United States. Hugh notes that shipping a container to the East Coast from Viet Nam used to cost $3,500 or $4,500 but now costs $5,000.
Coir’s Salinity Problem
When coconut husks were thrown in saltwater marshes just because there was no other place to dump them, they absorbed salt. These days, husks used in the coir industry are more likely to be soaked by rain or sprinklers than saltwater. Still, Hugh explains, coir is naturally high in salts, namely potassium and chloride.
Many nut trees and fruit trees that have husks have high levels of potassium, and coconut trees are no exception. The good thing about potassium and chlorides, according to Hugh, is that they are readily leachable. That means when the husks are flushed with freshwater, the salts will wash out.
In hydroponic growing systems that operate on a closed loop, it’s important to remove the salts. This can be accomplished through buffering, a process that uses calcium nitrate to replace the potassium with calcium and the chlorides with nitrates.
Calcium nitrate is a fertilizer but it is not organic, so buffering is not an option in organic growing. Calcium nitrate, when used in an open system, can pollute water bodies through nitrogen loading.
Coir in pots will leach salts every time you water the potted plants. Mature plants can tolerate the level of salt, and the more the plants are watered the less salt the pots will contain. However, when working with seedlings, the salt in coir is too much. Seedlings are very sensitive to soluble salts.
I have experimented with flushing coir. Starting with off-the-shelf coir products, I put coir on a window screen and sprayed it with water for several minutes in an attempt to purge the salts. I was hoping I would notice a difference, but when I compared purged coir to un-purged coir, I didn’t see any difference in my seedlings.
Hugh says washing coir is a bit more complicated than what I tried. Coir needs to be saturated with water before the salt ions are freed. “Hydrate, and then you can leach,” he says.
Testing Coir’s Salt Level
You can use an electrical conductivity meter to figure out if the salt content of coir has been reduced enough. Hugh recommends starting with a ratio of two parts water and one part hydrated coir, waiting 10-30 minutes, and then taking a reading of the water substrate. For seedlings, an EC reading of fewer than 0.5 millisiemens is the goal. For transplants, the EC could be as high as 1.5, Hugh says.
You can use distilled water for an easy, accurate reading. If you use tap water, test the EC of the tap water before mixing it with coir. Deduct the EC of the tap water from the EC reading of the substrate, and that will give you an accurate number.
Don’t Press Coir
Coir that has been over-compressed will be hydrophobic, which is the opposite of what’s needed to start seeds. Hugh says if a coir product doesn’t absorb water quickly, don’t use it for germination.
Coir is not a sponge, Hugh notes. If you press it down into a seed tray or pot, it will not spring back up the next time you apply water. Refrain from packing down coir so it retains that vital airspace.
Hugh also points out that the surface of coir dries out fast compared to peat. If starting a seed that sits on the surface of the growing medium, add vermiculite or fine sand to the top of the coir to maintain moisture contact with the seed.
I hope you enjoyed my conversation with Dr. Hugh Allen Poole and learned something new about coir. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
Have you used coir successfully to start seeds or make potting mix? Let us know in the comments below.
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