Coir has become one of the most important raw materials in modern substrates, especially now that growers want to use less peat. But coir is not a single product. The husk of the coconut yields several fractions with very different properties. Once you know them, you can use them in a targeted way.
Where does coir come from?
The husk is the thick, fibrous layer between the outer skin and the hard nut. Once the nut has been harvested, the husk is left over. It is processed into fibres, chips and a fine, spongy material: coir pith. For substrates, the pith (fine coir) and the fibres and chips (coarse coir) are what matter most.
Fine coir: the water holder
Fine coir, also known as coir pith, is the closest to peat in terms of function. It has many small pores and holds a lot of water. Its big advantage over peat: it quickly takes up water again, even after drying out. A dried-out pot with a lot of coir is therefore easier to rewet.
- High water-holding capacity
- Good rewetting
- Stable structure that breaks down slowly
- pH roughly neutral
That makes fine coir the logical basis for peat-reduced and peat-free mixes, for propagation and for pot plants that need consistent moisture.
Coarse coir: air and structure
Coarse coir consists of fibres and chips. It holds little water itself, but creates large pores and therefore air and drainage. More importantly still, it is very structurally stable. Where wood fibre breaks down and slumps after a few months, coarse coir keeps its shape for a long time.
- High air content
- Excellent structural stability
- Low water-holding capacity
- Light, even in large volumes
Coarse coir works well in container growing, in mixes for tub plants and in substrates for plants that need an airy, coarse medium, such as orchids and many aroids.
Washing and buffering
Coir naturally contains sodium and potassium, which come from the environment in which the palm grows. The exchange sites in the material are partly occupied by those elements. Untreated coir can therefore release potassium and sodium during the crop and lock up calcium and magnesium, leading to deficiencies.
For use in substrates, coir is therefore washed to remove excess salts and buffered with a calcium and magnesium solution. After buffering, the exchange sites are filled with elements the plant needs. The coir in our products is washed and buffered. If you source coir elsewhere, always ask whether this is the case, and measure the EC if in doubt.
Combining fine and coarse
The strength of coir lies in the combination. By mixing fine and coarse coir, you can set the air-water balance without depending on other raw materials. As a rule of thumb:
- Mostly fine, a little coarse for propagation, small pots and crops where consistent moisture is important.
- Roughly equal parts or more coarse for larger pots, long crops and outdoor growing with a risk of heavy rainfall.
- Mainly coarse for epiphytes and plants that need to dry out quickly.
In practice, fine and coarse coir are often supplemented with perlite for extra air, wood fibre for lightness, or a share of peat for familiar growing behaviour.
What to watch with coir-rich substrates
- Coir is roughly neutral; after switching from peat, the pH responds differently to lime and irrigation water.
- Preferably water more often and give less each time, especially with a high proportion of coarse coir.
- Compressed coir in blocks or bales must be thoroughly broken up and moistened before use, so that it regains its volume.
- Check the EC during the first few weeks, especially if you mix your own.
Coir in our mixes
Fine and coarse coir are a regular component of many of our peat-reduced and peat-free mixes. They are available separately for your own mixes, ready-made in one of our substrates, or in the ratio of your choice in a bespoke mix.
