Spike's Grow School
Coco Coir Explained
If you’ve ever killed a plant by loving it too much, coco coir is a forgiving place to start again. It holds water and air at the same time, resists going stagnant, and behaves predictably once you learn its one quirk. That mix of forgiving and consistent is why it’s the crowd favourite of hydroponic media.
But coco has a personality quirk that trips up more beginners than any other medium. Unlike clay pebbles or perlite, it doesn’t just sit there politely holding your nutrient solution. It gets involved. Understand that one quirk and everything else about growing in coco falls into place.
This is the deep dive from our guide to hydroponic growing media. We’ll cover what coco actually is, the types you’ll see on the shelf, why it behaves the way it does, how to feed and water it, and how to get a second and third life out of it. Grab a cuppa, there’s a fair bit here.
What is coco coir?
Coco coir is made from the fibrous husk of the coconut, the layer that sits between the hard inner shell and the smooth outer skin. It’s a by-product: the coconut is grown for its flesh, water and oil, and the husk was long treated as waste. Processing turns that husk into a growing medium by soaking, drying, ageing, screening and, in most cases, washing it to bring the salt levels down.
You’ll usually buy it one of two ways: compressed into bricks, blocks or slabs that expand when you add water, or loose and ready to use. Compressed coir is light and cheap to ship, then swells to many times its packed size once hydrated.
The important thing to hold onto is that coco is a soilless medium. It contains next to no nutrients of its own, so it doesn’t feed your plant; you do, through your nutrient solution. What it brings to the table is a genuinely good balance of water retention and aeration, a naturally near-neutral to slightly acidic pH, and a high lignin content that makes it tough and slow to break down. That durability is why, unlike peat, you can reuse it (more on that below).
The types of coco coir
"Coco coir" is really an umbrella term. The husk is separated into different fractions, and which one you use changes how the medium behaves.
Coco pith (coco peat)
The fine, dust-like, sponge-textured fraction. Pith is the water holder: it soaks up and retains a large amount of moisture, but on its own it packs down and holds relatively little air. This is the "default" coco most people picture, and it’s the base of most bagged products.
Coco fibre
The longer, stringy strands. Fibre adds structure and air pockets, which is why it’s often blended back in with pith to stop the mix compacting.
Coco chips (coco croutons)
Chunky pieces of husk, roughly one to two centimetres across. Chips create large air pockets and drain quickly, behaving a bit like clay pebbles, so they keep plenty of oxygen at the roots. The trade-off is that they dry out faster and need watering more often. They suit hydroponic setups and chunky-loving plants like orchids and aroids.
Blends (and the classic 70/30)
Most growers don’t use a single fraction; they use a blend. Commercial substrates mix pith and fibre (sometimes chips) in controlled ratios to hit a target balance of water holding and air. The best known is a blend of around 70% coco to 30% perlite: the coco holds moisture while the perlite keeps things open and airy. It’s the mix the majority of hobby growers reach for. (Full rundown in our perlite guide.)
Why coco isn’t truly inert (and what CEC really means)
Here’s the quirk everything hinges on. Genuinely inert media, clay pebbles, perlite and rockwool, simply hold water and air and hand your nutrient solution straight to the roots. Coco doesn’t. It takes part in the chemistry.
Coco’s fibres carry a mild negative electrical charge on their surfaces. Negative attracts positive, so those surfaces grab and hold positively charged nutrient ions, called cations (calcium, magnesium, potassium, sodium and others). The measure of how many cations a medium can hold this way is its cation exchange capacity, or CEC. Truly inert media have almost none. Coco has a meaningful amount.
How much? This is where honesty matters, because it genuinely varies. Coco has a moderate cation exchange capacity, so it holds and trades nutrients with the root zone, though reported values vary so widely with source and test method that it’s best treated as a qualitative strength rather than a single number (Abad et al., 2002). That same study characterised 13 coir samples from Asia, America and Africa and found their properties differed significantly from one source to another, so the coconut’s origin, how it was processed, and the particle size all shift where a given batch lands. That’s why you’ll see very different figures quoted around the traps: there isn’t a single true value. For context, that puts coco well above inert media (near zero) but below sphagnum peat, squarely in the "moderate" band.
Why does this matter so much in practice? Because the same study found coir arrives naturally high in potassium and sodium and low in calcium and magnesium. Those exchange sites turn up already occupied by sodium and potassium. When you start feeding, the coir does a swap: it grabs the calcium and magnesium out of your nutrient solution (which it "wants") and releases its sodium and potassium in return. Left unmanaged, that means your plant shows calcium and magnesium deficiencies even though you know you fed them, because the medium got there first.
That single behaviour drives the next two sections: it’s why coco needs preparing, and why it’s fed a little differently to an inert medium.
The one catch: coco needs preparing
Because of that cation swapping, raw coco needs two bits of prep before planting. They sound similar but they do different jobs, and mixing them up is a classic beginner trap.
Rinsing flushes the coir with water to wash out the loose excess salts, mainly sodium and potassium, bringing the EC (a measure of dissolved salts) down to a safe level. Rinsing on its own does not solve the cation problem.
Buffering soaks the rinsed coir in a calcium- and magnesium-rich solution so those exchange sites get pre-loaded with calcium and magnesium before your plants go in. Once the sites are satisfied, the coir stops stripping those nutrients out of your feed. Rinsing clears the loose salts; buffering settles the chemistry. You want both.
The good news is you often don’t have to do it yourself. Plenty of quality bagged coco comes pre-rinsed and pre-buffered, which is the easy path, especially when you’re starting out. If you’d rather buffer it yourself, it’s simple in principle but detailed enough in practice that it deserves proper step-by-step treatment, so we’ve given it its own guide: how to buffer coco coir.
When you’re buying pre-buffered coco, quality and consistency still vary from brand to brand, so it pays to look for a recognised standard. The main one is RHP certification, a Dutch horticultural substrate standard (RHP is short for Regeling Handelspotgronden, or 'Potting Soil Trade Regulation', the Dutch quality scheme for growing media) that verifies the coir has been produced to consistent physical, chemical and biological specifications: properly washed and buffered, a low and stable EC, a stable pH, and screening for contaminants and pathogens. An RHP mark on the bag is a reliable shortcut to knowing you’re getting clean, grow-ready coco rather than a cheap, unbuffered, high-salt product that causes the very problems buffering is meant to prevent.
Spike's Tip: Never plant into raw, unbuffered coco and just hope. Either buy it pre-buffered, or buffer it yourself first. Skipping this one step is the number one reason new coco growers watch their plants go pale and hungry while swearing they fed them everything. They did. The coco ate it first.
Feeding and watering coco
Coco feeds from day one. Because it carries almost no nutrition of its own, there’s no reserve for your plant to coast on the way there is in soil. Every watering is effectively a feed, which is a blessing and a curse: you get precise control, but mistakes show up quickly with no buffer to soften them.
Cal-mag, usually throughout. Since coco keeps wanting calcium and magnesium (and even more so if you’re on soft or reverse-osmosis water, which starts low in both), many growers run a cal-mag supplement across the whole grow, not just at the buffering stage. A ratio of around three parts calcium to one part magnesium is common. One nuance worth knowing: some base nutrients are formulated specifically for coco and already carry enough extra calcium and magnesium to cover the medium’s appetite, in which case additional cal-mag may not be needed. With general or all-purpose base nutrients, though, we’d recommend running cal-mag to stay on the safe side.
This is why coco-specific nutrients exist. A nutrient line formulated for coco accounts for the calcium and magnesium the medium holds back and the potassium it releases, so what your plant actually receives lines up with what the label promises. It’s not marketing; it’s chemistry.
pH. Coir is naturally slightly acidic to neutral (Abad et al., 2002). For feeding, a slightly acidic root zone keeps the widest spread of nutrients available to the plant, so growers generally aim for a feed pH in the high 5s to low 6s and check their runoff to keep it there.
Watering. Coco holds a lot of moisture but drains freely, which makes it famously hard to overwater as long as your pots actually drain. Fine pith holds the most water and can turn soggy if you drown it; chips and heavy perlite blends dry faster and want watering more often. The usual rhythm is little and often rather than the occasional big soak.
Reusing coco coir
One of coco’s best tricks: unlike peat, it’s sturdy enough to reuse. That high lignin content gives it a structure that survives a grow cycle, so you’re not throwing money in the bin every harvest.
For most growers, two to three cycles is the realistic range, sometimes more with careful management, before the structure breaks down far enough that it holds too much water and too little air. Between grows the coir needs reconditioning: clearing out old roots, rinsing, re-buffering (as coco breaks down it exposes fresh exchange sites that need satisfying again), and managing any pathogens carried over from the last crop. That’s a genuine process with a few steps to get right, so we cover it properly in our guide on reusing and sterilising your media.
And when coir finally is spent, it doesn’t have to go to landfill. It composts, works as a mulch, or digs into garden soil as an amendment, so it keeps giving even after its hydroponic life is over.
Coco coir and the environment (the honest version)
Coco has a green halo, and it has genuinely earned part of it. But "eco-friendly" gets stamped on coir a little too freely, so here’s the straight version, good and bad.
The genuine upside. Coir is a by-product. The fibre and pith come from husks left over by the coconut food and oil industry, so using it puts a waste stream to work rather than growing something specifically to be dug up. Coconut palms crop year after year, which makes coir renewable on a human timescale.
Where it really counts is as a peat alternative. Coco’s biggest environmental win is replacing peat. Peat accumulates in bogs extraordinarily slowly, on average only about a millimetre a year (Swindles et al., 2025), so a single metre of peat can represent a thousand years or more of growth: it is not meaningfully renewable once dug. And peatlands are one of the planet’s great carbon stores. According to the IUCN, peat soils hold more than 600 gigatonnes of carbon, up to 44% of all soil carbon, more than the carbon in all the world’s vegetation including its forests combined, and draining them to harvest horticultural peat releases that stored carbon. Every bag of coir used in place of peat helps leave that carbon where it belongs.
The honest caveats. Coir is not impact-free:
- Transport and food miles. Coir is produced in the tropics, with India and Sri Lanka the dominant coir producers, while Indonesia and the Philippines lead in growing the coconuts themselves (Barrett et al., 2016). Reaching Australia means thousands of kilometres of freight, and that shipping carries a real carbon cost of its own. Compressing the coir into blocks packs more into each shipment and trims the per-bag footprint, but it doesn’t erase it.
- Processing. Turning raw husk into a clean, low-salt medium uses water for washing, and dust and effluent from coir processing are documented concerns in the regions where it happens. The washing and buffering that make coir usable in the first place also add notably to its cost and footprint (Barrett et al., 2016).
- Labour. Coir processing is dusty, labour-intensive work, largely carried out in lower-income producing regions, so working conditions and occupational health are a genuine consideration in the supply chain.
- Soil export. When husks are shipped overseas rather than returned to the groves, the organic matter and nutrients they contain leave the coconut-growing soils with them.
The balanced verdict. Coir is a strong, renewable, peat-free choice, and you can stretch that further by reusing it and by choosing suppliers with better processing and labour practices. But it isn’t the zero-impact miracle some labels suggest, and we’d rather tell you that plainly than wave a green flag and move on.
Frequently asked questions
Do I need to buffer coco coir, or can I just rinse it?
They’re different jobs. Rinsing washes out loose salts and lowers the EC; buffering pre-loads the medium’s exchange sites with calcium and magnesium so it stops stealing those from your feed. You want both, and rinsing alone won’t prevent the classic calcium and magnesium deficiencies. The easy route is to buy pre-buffered coco.
What’s the difference between coco coir, coco peat and coco chips?
They’re different fractions of the same husk. Coco peat (pith) is the fine, sponge-like part that holds the most water. Coco chips are chunky pieces that create air pockets and drain fast, a bit like clay pebbles. "Coco coir" is often used as the umbrella term for all of it, and most products are a blend.
Do I always need cal-mag with coco?
Usually, yes, especially on soft or RO water, because coco holds onto calcium and magnesium and your plant needs a steady supply. The exception is a base nutrient formulated specifically for coco that already includes enough; with general-purpose nutrients, run cal-mag to be safe.
What pH should I run in coco?
Aim for a slightly acidic feed, generally in the high 5s to low 6s, and check your runoff. That range keeps the widest spread of nutrients available to the plant.
How many times can I reuse coco coir?
Typically two to three grows, sometimes more with careful reconditioning, before it breaks down enough to hold too much water and too little air. Each time it needs clearing of old roots, rinsing and re-buffering.
Is coco coir actually eco-friendly?
Partly. It’s a renewable by-product and a genuinely good peat-free alternative, which is a real environmental win. But it’s shipped long distances, its processing uses water and has labour considerations, so it isn’t impact-free. Reusing it and choosing responsible suppliers helps.
Ready to give coco a go?
We stock coco, coco-perlite blends and everything you need to feed it, and because we’re a real shop with a real team in Youngtown rather than a drop-shipper, you can come and pick our brains in person. Browse our growing media to get started, and if you find it cheaper elsewhere our Price Beat Guarantee has you covered. Order before the daily cut-off and it goes out with same-day dispatch.
References
- Abad, M., Noguera, P., Puchades, R., Maquieira, A., & Noguera, V. (2002). Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology, 82(3), 241-245. https://doi.org/10.1016/S0960-8524(01)00189-4
- Swindles, G. T., Mullan, D. J., Brannigan, N. T., Fewster, R. E., Sim, T. G., Gallego-Sala, A., . . . Warner, B. (2025). Climate and water-table levels regulate peat accumulation rates across Europe. PLOS ONE, 20(7), e0327422. https://doi.org/10.1371/journal.pone.0327422
- International Union for Conservation of Nature. (2021). Peatlands and climate change [Issues brief]. IUCN. https://iucn.org/resources/issues-brief/peatlands-and-climate-change
- Barrett, G. E., Alexander, P. D., Robinson, J. S., & Bragg, N. C. (2016). Achieving environmentally sustainable growing media for soilless plant cultivation systems: A review. Scientia Horticulturae, 212, 220-234. https://doi.org/10.1016/j.scienta.2016.09.030
- RHP Horticulture. (n.d.). RHP quality certification for horticultural substrates. https://www.rhp.nl/