If you’ve scrolled through the ingredient list on a recently purchased bag of potting mix, done any researching on hydroponic gardening systems, or simply read up on any indoor gardening forums lately there’s a really good chance you’ve seen the term coconut coir. There’s also a really good choice you’re wondering exactly what it is and why you’d want to use it. The simple answer: coconut coir is a natural fiber product taking the horticultural world by storm as a growing media.
Coconut coir, also known as coco coir, is popular with a wide range of consumers: container gardeners, hydroponic growers, commercial nurseries, and even homeowners trying their hand at indoor gardening. Part of this explosion in popularity is due to its sustainability, benefits, and similarity to soil and peat moss.
How coir is produced
A waste product of the coconut harvesting process (particularly in Sri Lanka, and India), coir is actually helping to cut down on the amount of waste generated. All of the material from the husk to the inner shell used to be discarded without a second thought. Now, these brown and white fibers found between the shell and the outer coating of a coconut seed (1) that we known as coconut coir have many applications in gardening products.
To start the process the coconut husks are soaked in fresh or saltwater to soften them. If the husks are soaked in tidal waters they will absorb salt that needs to be flushed out at a later stage of the manufacturing process.
After the husks are softened, the coir is removed from the husks and laid out, allowed to dry for an extensive amount of time. This can often take up to a year, depending on the local conditions and the thickness of the coir. The longer the coco coir is allowed to mature this way the better quality the final product is.
The coir is then formed into bales and processed into various formats for use. Some manufacturers sterilize the product as a final step before packaging; others opt out of this as sterilization kills any beneficial bacteria.
Different types of coir products
During the manufacturing process, variations can be made that slightly affect the size and shape of the end product, tailoring it to specific uses. There are three common ways to purchase coconut coir: pith, fiber, and chips.
- Pith: This is what is known as the peat version of coconut coir and looks like finely ground coconut husks or peat moss. It must be aged properly and rinsed well to prevent the release of salts when used. Coco pith, or coco peat, is typically used as a component in potting mixes or as a soil conditioner. Use on its own for growing plants is not recommended since it so small and absorbent it can hold too much water and drown the roots of your plants.
- Fiber: After drying out extensively, the long fibers removed from the husks can be used without any further processing. This is what is often shaped into the liners used in hanging baskets or decorative arrangements. In this unprocessed form, coco fiber doesn’t have the same water retention as processed coir but helps increase the porosity and drainage of garden soils and potting mixes.
- Chips: Somewhere in the middle between pith and fiber is coco chips, that function like a natural type of expandable clay pellet. The chunks are large enough to create air pockets within a growing media or soil while helping to retain moisture.
Pros and cons of coconut coir
There are many positive aspects that make coco coir so popular, with its excellent water retention taking the primary lead. Coconut coir is known to absorb up to ten times its weight in water while still maintaining open pore space for oxygen movement.
- Slower to breakdown than other organic materials used in potting mixes or to amend garden soils. This means it needs to be replaced or regenerated less often.
- Can be compressed to about one-fifth of its size to make shipping much more economical than other inert materials.
- A good combination of excellent water retention, drainage, and aeration, giving the roots plenty of room to grow while providing lots of space for oxygen
- Has a pH level close to neutral conditions (5.2 - 6.8 typically), so there is no need to worry about its effects on nutrient availability.
- Antifungal properties reduce fungal growth and damping-off of seedlings.
- Promotes the growth of beneficial bacteria in the root zone due to the presence of natural lignins.
- Rich in hormones and bio-stimulants to promote plant growth and root health.
- Some sources may contain plant essential nutrients such as potassium, iron, copper, manganese, and zinc.
- Very hydrophilic and easy to rewet if it dries out.
- A highly available, renewable resource that reduces the amount of waste generated by processing coconuts.
Coconut coir typically comes in dried bricks and require rehydration in order to bring it back to life so to speak.
Like many other products though, coir does come with some negative aspects.
- Coconut coir doesn’t have much in the way of specific nutrients such as nitrogen, phosphorus, and potassium so you will need to fertilize your plants well to provide them the nutrition they need.
- A net negative charge on the coir fibers leads a what is known as a high cation exchange capacity (CEC). While this can be seen as beneficial, a high CEC also has the tendency to grab ahold and “tie up” calcium, magnesium, and iron, making them unavailable for plant uptake.
- High porosity is great for water infiltration, drainage, and aeration but on the downside, it means it doesn’t have the structure to keep plants upright as well as other growing media. Plants need to be staked or supported in another way.
- May contain a high salt content if the coconut fibers are rinsed with salt water during the manufacturing process. High-quality products are typically rinsed with fresh water at a later stage to flush out the salts; lower quality products may not be and can cause salt injury to your plants.
- Just prior to packaging and shipping, some lower quality products are treated with chemical agents to prevent any bacterial growth. These products will need to be soaked and rinsed thoroughly to remove the chemicals prior to use.
How to use coir
One of the attractive things about using coconut coir is it works well in a variety of different ways, making it a multi-function product.
- As a component of soilless potting mixes. It is typically mixed with components such as vermiculite, perlite, and perhaps another organic material such as compost or peat moss to create potting soil.
- As a soil amendment in the garden to increase the drainage and porosity of clay soils, or increase the water holding capacity of sandy soils.
- As a growing media for seed starting and propagation when rooting plant tissue cuttings. Maintains a high moisture content to keep seeds and cuttings from drying out, until roots form while natural anti-fungal properties prevent the growth of fungi and damping off.
- As a hydroponic growing medium and source of support for roots in hydroponic gardening systems. Its neutral pH doesn’t require correction before use, and a high CEC helps to keep nutrients within the root zone.
- As a growing media for certain exotic plants such as orchids, ferns, bromeliad type plants, and anthuriums. These plants prefer their roots to stay moist but not waterlogged and don’t care for much in terms of fertilizers.
- As an environmentally friendly mulch in both containers and in gardens.
How to not use coir
Truth be told, there really isn’t very many recommendations given on when to NOT use coir.
As mentioned above it can be used on its own for growing media when starting seeds, rooting plant cuttings, in hydroponic systems, and with some species of exotic plants.
The most common recommendation is to not use it as the only growing media when container gardening. Mix it with compost and add components such as perlite, vermiculite, sand, or pine bark to create a composite mixture.
Coco coir versus peat moss
A great deal of coconut coir’s popularity can be attributed to the controversy surrounding sphagnum peat moss and its use in gardening and hydroponics.
One of the drawbacks of using peat moss is that it is a non-renewable resource. There are many conservationists, wetland scientists, and even gardeners who are calling for a total boycott of peat and its byproducts.
There is also an environmental concern that comes with harvesting peat bogs across Canada and parts of the United States. Peatlands store a great percentage of carbon – about 10% of our earth’s fixed carbon. When they are harvested this carbon is released into the atmosphere, contributing to global warming. While producers are adamant their practices are sustainable, there has been an interest in moving towards products such as coconut coir as a replacement.
Coconut coir, on the other hand, is a suitable alternative, considering it is a renewable resource. An added bonus is that the production of it helps to reduce the amount of waste generated by coconut harvesting and manufacturing.
There are many reasons that coconut coir is quickly gaining popularity in both home and commercial gardens: excellent water retention, good drainage, ample aeration, close to neutral pH, natural anti-fungal properties, etc. As a renewable resource, it is overtaking peat moss as a component in potting soils, as a soil amendment, in commercial nurseries for seed starting and plant propagation, and even in hydroponic gardening.
- Sengupta, S. & Basu, G. (2016). Properties of Coconut Fiber. In Reference Module in Materials Science and Materials Engineering. doi: 10.1016/B978-0-12-803581-8.04122-9