The short answer: coco peat is made from the spongy pith left over when coir fibre is pulled out of coconut husks. The husks are softened (by long retting in water, a short soak, or not at all), then torn apart in machines that separate the long fibre from the pith. The pith is sieved to a particle size, aged in heaps, washed with fresh water to bring the salts down, dried, and pressed into blocks, briquettes or grow-bag slabs. Each of those steps changes something a grower will notice later, which is why two coco peats that look alike can behave very differently.
Key facts
- The husk is about 35% of a coconut's weight. Fibre is roughly 30% of the husk, and pith with short fibre makes up most of the rest. You'll see pith quoted at anywhere from half to 70% of the husk.
- Traditional backwater retting takes six to ten months. Tank soaking can be a matter of weeks. Dry milling skips soaking altogether.
- Unwashed pith can test at 6 mS/cm or more in a 1:1.5 volume extract. Washed pith is normally below 1 mS/cm.
- Compressed coir sits at around 400 kg/m³ at about 20% moisture. Expanded and dried, the same material is closer to 70 kg/m³, so a block grows four to six times in volume when wetted.
Where coco peat starts: the husk
Nobody grows coconuts for coco peat. The nut is harvested for copra, oil, desiccated coconut or drinking water, and the thick fibrous husk around it (the mesocarp) is the by-product. Inside the husk, long fibres run through a corky, light material. That material is the pith. Once the fibre has been extracted, what's left is pith mixed with very short fibre and some dust and husk fragments. For every tonne of fibre a mill produces, it generates something like 2.3 tonnes of pith.
Most husk for the industry comes from mature, brown nuts. Husks from younger, greener nuts are the traditional raw material for retted white fibre. For the basics, see what coco peat is.
Step 1: Softening the husk (or not)
The fibre is glued into the husk by pectins, phenolic compounds and other binding material. There are three ways the industry deals with that.
Backwater retting. The oldest method. Husks are bundled in nets or buried in pits along tidal backwaters and left under water while bacteria and fungi break down the binding material. It takes six to ten months, depending on water temperature, tidal movement and water quality. Bacterial cultures have been shown to cut this to about three months. The fibre is then beaten out, traditionally with wooden mallets, now mostly in machines. Retting gives the finest, lightest-coloured fibre, used for spinning yarn.
Soaking. Husks are soaked in tanks or ponds, or sprinkled and shredded, for a much shorter time, then sent to the machines. Depending on the ripeness of the husk and the system, retting and soaking can run from about two weeks to six months.
Dry milling. Dry or semi-dry husks go straight into the machines with no soaking. This is the main route for brown fibre, and it's where a large share of horticultural pith comes from.
The route matters for the pith. Pith that has spent months in brackish backwater has been through a long biological process and carries whatever salt the water held. Pith from dry milling is fresher and keeps the soluble salts and phenolics the husk grew with. Neither is ready for a greenhouse straight out of the mill.
Step 2: Decorticating and defibering
Two kinds of machine do the separating, and you'll hear both names in the trade.
- Defibering (combing). Husks are held against fast-spinning drums set with steel spikes. The spikes comb out the binding material and the pith, and the long, stiff bristle fibre comes off one end.
- Decorticating (beating). Soaked or dry husks are fed into a machine where bars on a rotor beat and shred them. The output is a mixed fibre (long and short together) plus pith.
Whatever the machine, raw pith falls out below. It contains fine particles, short fibres of a few millimetres, bits of husk skin, and some sand. At this point it's a waste stream.
The fibre goes on to its own markets as bristle, mattress and mixed grades. The pith is what we follow from here.
Step 3: Sieving and grading
Raw pith is screened to take out long fibre, lumps and sand, and to set the particle size. The mesh decides the physical behaviour of the finished product. The most common horticultural grade is pith sieved through a quarter-inch (about 6 mm) screen, which gives an air content of about 20%. Finer sieving gives a wetter, denser product for propagation. Coarser fractions, cut fibre and husk chips are added back for crops that need more air. Adding chips can lift the air content of a mix by 10 to 40%, depending on how much is used and how big the pieces are.
This is also where blends are made, from pith alone to long-life mixes with more chip and fibre. We cover sieve grades and what they're used for in coco peat particle size grades.
Step 4: Ageing
Fresh pith is physically and chemically young. It has a high share of cellulose relative to lignin, so if it goes straight into a slab it breaks down during the crop, gets finer and wetter, and loses air. It also carries phenols that are toxic to roots. Producers therefore store sieved pith in heaps for months, where microbes eat the easy carbon and rain and time leach out much of the phenolic material. The colour darkens from tan to brown.
There's no single standard for how long. The details, and how to tell aged from fresh, are in aged vs fresh coco peat.
Step 5: Washing
Coconut palms grow happily in salty coastal ground, and the husk stores what the palm doesn't use. The free salts are mainly sodium, potassium and chloride. They're loosely held, so fresh water washes them out. In practice the pith is soaked or flushed in tanks or beds and drained, and the cycle is repeated until the runoff tests low enough. Unwashed pith can read 6 mS/cm or higher in a 1:1.5 volume extract. Properly washed pith is normally under 1 mS/cm.
Two things decide how well washing works. The first is the water. Salty water can't wash salt out, and unusually salty coir is often traced back to poor wash water. The second is time and volume. Each pass replaces salty water held in the pith with cleaner water, so it takes several passes.
Some producers then buffer the pith by soaking it in a calcium nitrate solution (sometimes with magnesium), which swaps sodium and potassium held on the exchange sites for calcium. That's a separate, optional step, covered in buffered vs unbuffered coco peat. At CVM Fiber and Industries, coco peat is washed with water to reduce EC. No calcium nitrate or other chemicals are used, and it is not buffered.
Step 6: Drying
Washed pith is far too wet to press. It's dried in the sun on open yards or in hot-air dryers until it's down to roughly the moisture it will be pressed at, around 20%. Sun drying depends on the weather, so output slows in the wet months. Material that's too wet at pressing makes heavy blocks that can go mouldy in transit. Material that's too dry is harder to compress and rewet evenly.
Step 7: Compressing
Dried pith is weighed and pressed in hydraulic presses. Compression is about freight: a pressed block is several times denser than the loose, dry material, so far more coir fits in a truck or container. The common formats:
| Format | What it is | Typical use |
|---|---|---|
| 5 kg block | A large pressed brick of pith, chips or a blend | Mixing into potting media, nurseries, greenhouses |
| 650 g briquette | A small brick, roughly a tenth of the weight | Retail, propagation, small growers |
| Grow bag or slab | A flat compressed slab sealed in a plastic sleeve | Hydroponic tomatoes, peppers, cucumbers, berries |
| Open-top bag | A compressed block in a bag with an open top, expanded by the grower's first watering | Strawberries, cane fruit, nursery stock |
| Loose bale | Pith pressed into large bales for remixing | Potting mix and substrate producers |
Pressing changes some physical properties of the pith, but it shouldn't stop it rewetting. When the grower adds water, the block expands back to four to six times its compressed volume, with the exact figure depending on how much fibre and chip is in it. Hydrating and checking blocks is covered in our coco peat blocks guide.
Step 8: Bagging and packing
Grow bags are made by sealing a compressed slab into a printed or plain film sleeve, sometimes with drainage slits and plant holes pre-cut. The slab only swells to full height once it's placed and irrigated in the greenhouse. Blocks and briquettes are wrapped or bagged, stacked on pallets and stretch-wrapped. Some origins also require fumigation or inspection of the shipment before export, and each importing country sets its own plant-health rules.
What to ask a supplier about their process
Ask:
- Is the pith from retted, soaked or dry-milled husk?
- What sieve size, and is there chip or fibre in the mix?
- How long is it aged before washing?
- How is it washed, and what's the EC of the wash water?
- Is it buffered, and with what?
- What moisture is it pressed at?
Then test a sample yourself. The answers explain most of the differences you'll see between suppliers.
If you'd like to talk through which formats and blends suit your crop, get in touch with us.
FAQ
How long does it take to make coco peat from a husk?
It depends mostly on the softening step and the ageing time. Backwater retting alone takes six to ten months, while dry-milled pith is produced within days of milling. Ageing then adds months, and washing, drying and pressing add days to weeks depending on the weather.
Is coco peat made with chemicals?
Basic coco peat isn't. It's sieved, aged, washed with water, dried and pressed. Some producers buffer it with calcium nitrate, and some retting operations use additives, but neither is needed to make washed coco peat. Ask your supplier exactly what, if anything, has been added.
What is the difference between washed and buffered coco peat?
Washing uses fresh water to flush out free salts such as sodium, potassium and chloride, which lowers EC. Buffering is an extra soak in a calcium (and sometimes magnesium) solution that swaps sodium and potassium held on the exchange sites for calcium. Washed coco peat can be unbuffered, and many growers use it that way.
Why is coco peat compressed?
To save freight. Dry, loose pith is very light and bulky, so pressing it into blocks, briquettes or slabs lets far more product fit into each shipment. The grower adds water and the material expands back to four to six times its pressed volume.
Is coco peat a waste product?
It starts as one. Pith is what's left after the fibre is taken out of the husk, and mills without a buyer for it pile it up. Processing it into a growing medium turns that by-product into something useful, but it still needs sieving, ageing and washing before it's fit for plants.
Does the retting method affect coco peat quality?
It can. Pith from long retting in brackish backwater has been through months of microbial activity and may carry salt from the water. Pith from dry milling is fresher and holds the husk's own salts and phenolics. Both can make good coco peat if they're aged and washed properly.