In short: Coco coir's main downsides are that it contains almost no nutrients, unbuffered coir locks up calcium and magnesium, poorly washed coir can be salty, neat coir can stay too wet in pots, its pH (5.5–6.5) is too high for ericaceous plants, and quality varies a lot between brands. Every one of these is avoidable: buy washed, buffered coir with a published pH and electrical conductivity (EC), blend it with compost and perlite, and feed your plants. Blue Apple Garden's bricks, for example, are washed and calcium-buffered with pH 5.5–6.5 and EC below 0.5 mS/cm published, which deals with the lock-out, salt and consistency problems before you start; they still need blending and feeding.
Coco coir — also called coco peat — is one of the best peat-free growing media you can buy. It holds water and air at the same time, re-wets easily and stores as a compact brick. But it is not perfect, and most of the problems people have with it come from a handful of predictable causes. Here they are, with the fix for each.
The downsides at a glance
| Downside | What you see | How to avoid it |
|---|---|---|
| 1. Almost no nutrients | Pale, slow plants after a few weeks | Blend with compost or feed from the start |
| 2. Calcium and magnesium lock-out (unbuffered coir) | Yellowing between leaf veins; blossom end rot on tomatoes | Buy buffered coir, or buffer it yourself |
| 3. Salt in poorly washed coir | Burnt seedling tips, poor germination | Choose coir with a stated EC below 0.5 mS/cm |
| 4. Can stay too wet when used neat in pots | Soggy compost, root rot, fungus gnats | Add 20–30% perlite; let the surface dry |
| 5. Not acidic enough for ericaceous plants | Yellow leaves on blueberries, camellias | Use an ericaceous mix with conifer bark |
| 6. Surface mould and fungus gnats | White fuzz or small black flies | Water less often, improve airflow |
| 7. Quality varies between brands | Chunky, dusty or salty batches | Buy from suppliers who publish their specification |
| 8. Breaks down over a few seasons | Slumping, slower drainage | Top up with fresh coir; compost it after 2–3 seasons |
| 9. Long supply chain | Shipped from South Asia | Choose compressed bricks; reuse and compost it |
1. Coco coir contains almost no nutrients
Coir is a physical growing medium, not a fertiliser. Seedlings live off their seed for a week or two, but anything grown on in neat coir will go pale and stall without food. Fix: blend it with peat-free compost (30–50% is typical for pots and beds) or use a liquid feed from the first true leaves. Our mix ratios for every plant show exactly how much to add.
2. Unbuffered coir locks up calcium and magnesium
Raw coir carries sodium and potassium on its exchange sites. When you feed, it swaps those for calcium and magnesium and holds on to them, so the plant goes short even though you are feeding correctly. The signs are yellowing between the veins of older leaves and, on tomatoes and peppers, blossom end rot (a calcium problem). Fix: buy coir that has been buffered — pre-treated with calcium at source — or soak unbuffered coir in a calcium–magnesium (Cal-Mag) solution before use. See buffered vs unbuffered coco coir.
3. Poorly washed coir can be salty
Coconut husks absorb salt, and some coir is processed with brackish water. Salty coir has a high electrical conductivity (EC), which scorches seedling roots and stops germination. Fix: buy coir with a published EC — below 0.5 mS/cm is a good benchmark — or rinse unknown coir thoroughly and test the run-off. How to test: coco coir pH and EC explained.
4. Neat coir can stay too wet in pots
Coir holds many times its weight in water. In a pot without drainage, or watered little and often, the lower layers stay saturated and roots rot. Fix: add 20–30% perlite for most container plants (more for cacti), make sure pots drain, and water when the top few centimetres feel dry rather than on a schedule. Ratios: coco coir and perlite mix ratio.
5. It is not acidic enough for ericaceous plants
Coir sits at about pH 5.5–6.5 — slightly acidic, which suits most plants. Blueberries, camellias, rhododendrons and azaleas need pH 4.5–5.5, so neat coir is not ericaceous. Fix: blend coir with composted conifer bark and pine needles. Recipe: is coco coir acidic?
6. Surface mould and fungus gnats
A white, fluffy growth on damp coir is usually a harmless fungus breaking down organic matter, and small black flies are fungus gnats breeding in a permanently wet surface. Both are signs of too much water and too little air rather than a fault in the coir. Fix: let the surface dry between waterings, increase airflow, and scrape off any fuzz; a thin layer of grit on top discourages gnats. A sour smell means the mix is waterlogged — repot with more perlite.
7. Quality varies a lot between brands
"Coco coir" covers fine pith, coarse fibre and chips, washed and unwashed, buffered and unbuffered. A bargain block can be dusty, chunky or salty, and expand to less than you expect. Fix: buy from suppliers who publish the pH, EC, whether it is buffered and how many litres a brick makes — see how to choose the best coco coir in the UK.
8. It breaks down over a few seasons
Coir lasts far longer than peat-free bark composts, but the fibre gradually breaks down. After two or three seasons it slumps and drains more slowly. Fix: top up with 10–20% fresh coir each season, and when it is spent, use it as a mulch or dig it into heavy soil. Guide: how to reuse and rehydrate coco coir.
9. It travels a long way
Most coir comes from India and Sri Lanka, so it carries a shipping footprint, and washing it uses water. It is a renewable by-product of the coconut industry rather than a mined material like peat, and compressing it means far less volume is shipped: our 5 kg brick measures 30 × 30 × 14 cm and expands to about 75 litres, roughly six times its packed size. We set out exactly what we do and do not claim on our sustainability claims page.
Plants that don't like coco coir (used neat)
| Plants | Why neat coir doesn't suit them | What to use instead |
|---|---|---|
| Blueberries, camellias, rhododendrons, azaleas | pH too high | Ericaceous coir and bark mix |
| Cacti and succulents | Holds too much water | Half coir, half grit or perlite |
| Mediterranean herbs (lavender, rosemary, thyme) | Prefer lean, very free-draining soil | Gritty mix with no more than a third coir |
| Alpines | Need sharp drainage | Gritty alpine mix; coir only as a small part |
| Long-term shrubs in big containers | Coir slowly breaks down over the years | Loam-based compost, with coir to lighten it |
Almost everything else — seedlings, vegetables, tomatoes, strawberries, houseplants, orchids (blended with bark), hydroponics and lawn seed — grows well in coir that is buffered, blended and fed.
So is coco coir still worth using?
Yes, for most jobs. The downsides above are about choosing the right coir and using it correctly, and the upsides are real: it holds water and air at the same time, re-wets easily if it dries out, is peat-free, and a 5 kg brick expands to about 75 litres. Start with coir that is washed and buffered, blend it for the plant you are growing, and feed — and most of the problems disappear.
Frequently asked questions
What are the downsides of using coconut coir?
It has almost no nutrients, unbuffered coir locks up calcium and magnesium, poorly washed coir can be salty, neat coir can stay too wet in pots, it is not acidic enough for ericaceous plants, and quality varies between brands. Buying washed, buffered coir and blending it with compost and perlite avoids nearly all of these.
What plants don't like coco coir?
Ericaceous plants such as blueberries and camellias (the pH is too high), and plants that need very sharp drainage — cacti, succulents, alpines and Mediterranean herbs — when the coir is used neat. Mixed with grit, bark or perlite, coir works for these too.
Can mould grow on coco coir?
Yes. A white, fluffy growth on damp coir is usually a harmless fungus feeding on organic matter. It is a sign the surface is staying too wet; let it dry between waterings and improve airflow.
Why are my plants turning yellow in coco coir?
The two usual causes are hunger, because coir contains almost no nutrients, and calcium or magnesium lock-out in unbuffered coir. Feed regularly, and use buffered coir or a Cal-Mag supplement.
Is coco coir bad for the environment?
It has a shipping footprint because it comes from South Asia, but it is a renewable by-product of the coconut industry rather than a mined material like peat. Compressing it into bricks, reusing it and composting it at the end reduce its impact.
Washed, calcium-buffered coco coir with a published pH (5.5–6.5) and EC (below 0.5 mS/cm), tested on every batch — delivered free across the UK.
Shop buffered coco coir → Why we buffer