Coco Coir for Mushrooms: Substrate, Casing, Pasteurising

The short answer: coco coir is used in mushroom growing for two jobs. As a bulk substrate ingredient (the "CVG" mix of coir, vermiculite and gypsum) it holds water and gives structure while adding almost no food, which keeps contamination pressure low. As a casing layer for button mushrooms (Agaricus bisporus) it is a tested peat substitute: in Spanish trials a limed coconut-fibre casing gave a biological efficiency of 92.7 kg per 100 kg of compost against 89.6 for the peat control. Coir does not feed gourmet species on its own, so oyster, shiitake and lion's mane growers pair it with straw, sawdust or bran.

Key facts

Pure coconut fibre pith casing held 5.45 kg of water per kg and had a total pore space of 942 mL per litre, against 3.00 kg/kg and 894 mL/L for a sphagnum peat and lime casing (Pardo-Giménez and Pardo-González, 2008).

Coir pith contains roughly 48% lignin; on its own it gave Pleurotus florida a bioconversion efficiency of about 25%, rising to 110–125% when mixed with rice straw or horse gram residue (Shashirekha and Rajarathnam, 2007).

The common CVG recipe is 1 part coir to 1 part vermiculite by volume, with gypsum optional (GroCycle); supplier recipes for a 650 g brick use 250 g to about 300 g of vermiculite, 50–100 g of gypsum and 3.5–3.8 litres of hot water.

Hot-water pasteurisation is quoted at 65–75 °C for 1–2 hours (GroCycle) or 82 °C (180 °F) for 1–2 hours (North Spore). Sources disagree on the ceiling; see below.

Casing EC matters: around 1.6 dS/m was found to be the threshold above which yield fell substantially (Pardo et al., 2004, cited in Pardo-Giménez and Pardo-González, 2008).

Why coir is used in mushroom growing

Three properties explain it.

Water holding. A casing or bulk substrate has to act as a water reservoir for the developing mushrooms. In the 2008 Spanish casing trial, pure coconut fibre pith held 5.45 kg of water per kg of dry material, more than the peat-based control (3.00 kg/kg) and far more than the mineral soil control (0.61 kg/kg). In an Iranian trial the coco peat casing had a water-holding capacity of 533%, against 140% for the commercial casing soil (Ghasemi et al., 2020).

Structure and air. Coir pith is a stable, porous material. Total pore space in the Spanish trial was 942 mL/L for pure coir pith, the highest of the eight casings tested, and the dry bulk density was only 0.119 g/cm³. High porosity helps gas exchange around the mycelium; the same paper notes that porosity correlated positively with mushroom numbers in earlier work.

Low nutrient content. Coir pith is mostly lignin and cellulose with little available nitrogen. Shashirekha and Rajarathnam (2007) put the lignin content at about 48%; a Bhutan Ministry of Economic Affairs project profile quotes 31% lignin, 27% cellulose and a C:N ratio of 104:1, so the published figures vary with source and processing. Whichever figure you take, coir is a poor food for competitor moulds and bacteria as well as for mushrooms. That is why growers pasteurise coir rather than sterilise it, and why it is a sensible base for a low-risk bulk substrate rather than a complete feed. The low nutrient content is also why it does so little harm as a casing: the Iranian authors note that mineral content in a casing is not needed and can even be a limiting factor.

If you are new to the material, what coco peat is and how it is made covers the basics.

Coir as a bulk substrate: the CVG mix

CVG stands for coir, vermiculite and gypsum. It is the standard hobby and small-farm bulk substrate for species that fruit from a nutrient-poor, moisture-holding bed once grain spawn has been mixed in. It is also used as a cheap filler in manure-based mixes: GroCycle's substrate guide gives two parts manure to one part coir for button mushrooms.

Ratios and hydration

Published recipes differ, mainly because some are by volume and others by weight.

Source	Coir	Vermiculite	Gypsum	Water	Notes
GroCycle (coco coir substrate guide)	1 brick, about 650 g	8 cups dry (1:1 by volume once coir expands)	1 cup, optional	16 cups (about 3.8 L) boiling	Brick expands 5–7 times in volume
Bootstrap Bee	650 g brick	8 cups fine, dry	1 cup	16 cups at 74 °C (165 °F)	Cool at least 6 h before spawning
La Mycosphère (product sheet)	about 650 g	about 250 g dry	about 50 g	3.5 L boiling	Second version uses 300 g vermiculite, 100 g gypsum

The ratio is not critical. What matters is that the finished mix sits at field capacity (below) and that the vermiculite is horticultural grade. Perlite adds nothing useful inside the substrate; GroCycle recommends keeping it for the fruiting chamber floor.

For large batches, growers hydrate 5 kg blocks rather than briquettes. Block hydration volumes and how to break a block apart are covered in the coco peat blocks guide; the mushroom-specific point is to use hot water so the hydration step doubles as pasteurisation.

Spawn rate

GroCycle recommends a minimum spawn rate of 20% for a coir and vermiculite mix, and 50% for plain coir to speed colonisation. La Mycosphère suggests about 1 part grain spawn to 4 parts substrate, noting that 1:3 or 1:2 works but costs more. North Spore pairs one spawn bag with two to four bags of sterile CVG. Higher spawn rates colonise faster and leave less time for contaminants to establish, which matters more with pasteurised than sterilised substrate.

Which species

Be realistic about what coir can do alone. GroCycle states that gourmet varieties generally need richer substrates such as hardwood sawdust, and that a substrate needs roughly 1–2% nitrogen; coir supplies little of that. The research record is mixed:

Coir pith alone gave Pleurotus florida about 25% bioconversion efficiency; hot water, acid and alkali pretreatments did not help, but mixing with rice straw or horse gram residue raised efficiency to 110–125% (Shashirekha and Rajarathnam, 2007).
In a Bangladeshi trial, coconut coir gave the highest biological yield (186.06 g per bag) and economic yield (180.64 g) for Pleurotus ostreatus against sawdust, sugarcane bagasse and their mixtures (Das et al., 2014). The coir used in that study was coarser husk material rather than fine pith, which likely explains part of the difference.

For a commercial oyster, shiitake or lion's mane operation, treat coir as a moisture-holding and structural component, not the main feed. Supplemented sawdust or straw remains the energy source; coir can replace part of it to improve water holding and reduce substrate cost. Once you add bran or other supplements, GroCycle notes that sterilisation rather than pasteurisation becomes necessary.

The field-capacity test

Mushroom substrate and casing should be wet but not waterlogged. The standard check, described identically by GroCycle, La Mycosphère and Bootstrap Bee, is the squeeze test:

Take a handful of mixed, cooled substrate and squeeze it firmly.
It should hold together as a clump and release only a few drops of water.
A stream of water means it is too wet: add dry coir or vermiculite, or spread it to evaporate.
No drops and a crumbling clump means it is too dry: mist in more water and mix again.

For casing, the Spanish trials ran the layer at 70–80% of its water-holding capacity, topping up with 0.5–1.5 L/m² as needed (Pardo-Giménez and Pardo-González, 2008). Because coir holds so much water, it is easy to overwater and seal off the air pores; check with the squeeze test rather than a schedule.

Pasteurising coco coir

Pasteurisation reduces the number of competing organisms while leaving some heat-tolerant bacteria that help protect the substrate; sterilisation kills everything and demands sterile spawning conditions (GroCycle pasteurisation guide). Coir can carry moulds, bacteria and insect eggs from processing and storage, so most growers pasteurise it even though its low nutrient content makes it less risky than straw or manure. North Spore describes pasteurising its coir as optional for the same reason.

Method	Temperature	Time	Source	Suits
Hot-water soak	65–75 °C (149–167 °F)	1–2 h	GroCycle	Small batches, buckets
Hot-water bath	82 °C (180 °F)	1–2 h	North Spore	Loose coir for casing
Bucket method	Boiling water poured on, lid on, insulated	Rest 6–8 h (La Mycosphère) or 8–12 h (Zombie Myco)	Supplier guides	Bricks; hydrates and pasteurises in one step
Oven	Core 71–82 °C (160–180 °F); 71–74 °C for 1 h	Check after 60 min	GroCycle; Zombie Myco	Casing, small volumes
Steam, whole room or bed	At least 66 °C (150 °F) bed temperature	At least 10 h	Penn State mushroom facility	Farm-scale beds, post-crop cook-out
Spent compost before reuse as casing	70 °C	12 h	Pardo-Giménez and Pardo-González (2008)	Research practice

Two cautions. First, the sources disagree about the upper limit: Zombie Myco warns that above 82 °C (180 °F) you move from pasteurising to sterilising and lose the useful microbes, while North Spore quotes 180 °F as its target. Pick one method and keep it consistent. Second, mass takes time to heat. Penn State measured about 14 hours for a bed to reach 60 °C regardless of air temperature; with a bucket of hydrated coir, use a probe thermometer in the centre rather than trusting the water temperature at the top.

The Indian and Spanish research trials treated casing chemically (formalin and fungicides) before use. That reflects research protocol in those countries and is not something to copy on a food farm without checking local regulations; heat is the usual route.

Coir as a casing layer for button mushrooms

Casing is the layer spread over colonised compost to trigger fruiting. Pardo et al. (2004) list its roles: physical support for the mushrooms, holding humidity, hosting the bacteria that stimulate pinning, protecting the compost surface from drying, providing an aerated environment, and keeping osmotic pressure (salt concentration) low. Sphagnum peat has been the standard material in Europe and North America because of its water holding and structure. Coir is the most studied substitute, and the results depend heavily on how it is prepared.

Study	Casing compared	Result for coir	Notes
Pardo et al. (2004), Spain	Soil mixed 4:1 with sphagnum peat, black peat, pine bark, coconut fibre pith or wood fibre; three strains	Soil + coir pith gave the highest total yield for strain Pla 8.9 (20.94 kg/m², BE 30.36) and was level with peat for the other two strains	No difference in earliness; no significant difference in colour or texture
Pardo-Giménez and Pardo-González (2008), Spain	Pure coir pith and coir:spent compost blends, all limed with 100 g/L CaCO₃, vs peat + lime and soil + coir controls	Pure coir pith BE 92.7 kg/100 kg compost; 4:1 coir:spent compost 92.9; peat control 89.6	Yield fell as spent compost (and EC) rose
Saini et al. (2021), India	Seven materials alone (sawdust, FYM, vermicompost, soil, coir pith, spent compost, FYM + soil)	Coir pith best on every measure: 55.3 fruit bodies, 0.679 kg per 5 kg compost, BE 33.95%, vs 10.5% for local soil	Low-tech bamboo-hut conditions
Ghasemi et al. (2020), Iran	Commercial casing soil, spent compost, coco peat, vermicompost at 2, 4 and 6 cm	Coco peat worst: 4.43 kg/m² vs 27.03 for commercial casing; delayed first flush	Coco peat was pH 5.85, EC 2.99 dS/m, unlimed

The Iranian result looks like a contradiction until you read the material properties. That coco peat was acidic (pH 5.85) and salty (EC 2.99 dS/m). The authors point out that the pinning bacteria (Pseudomonas spp.) want pH 6–7 and that the EC threshold for casing is about 1.6 dS/m; they recommend liming and leaching to fix it. The Spanish trials added 100 g of calcium carbonate per litre of coir, which brought the pH to 8.86 and the EC to 437 µS/cm (0.44 dS/m), and the coir performed at least as well as peat. The lesson for growers is simple: coir casing must be low in salts and limed to about pH 7.5 or above before use.

Practical casing notes

Depth. The Spanish trials used 3 cm. Ghasemi et al. found 4 cm gave the heaviest mushrooms and largest caps, with 2 and 6 cm no different from each other. For gourmet species in tubs, North Spore recommends only a thin layer of 6–12 mm (¼–½ inch), applied once the substrate is fully colonised and primordia are forming.
Liming. Add calcium carbonate (or a sugar-beet lime, as the Spanish peat control used) before pasteurising. The 100 g/L rate above is a research figure, not a universal recipe; check the pH after mixing.
Moisture. Case at field capacity and maintain 70–80% of water-holding capacity. Coir casing dries at the surface faster than it looks; water little and often.
Mixing. Coir blends well with mineral soil (the Castilla-La Mancha commercial casing was soil and coir pith 4:1) and with washed spent compost (4:1 coir:spent compost matched the peat control).

Contamination risk and hygiene

Coir's low nutrient content keeps contamination pressure down, but it is not sterile and not immune. GroCycle lists the practical risks: salt left from husks soaked in brackish water, chemical residues from processing, and inconsistent quality between bricks. The Spanish casing trial routinely tested its coir for mites, nematodes and Trichoderma before use and found all negative in the pasteurised material; that is the standard you want from a supplier, and heat treatment on arrival is your insurance.

Routine measures:

Pasteurise coir for casing and for any bulk mix spawned outside a clean room.
Hydrate in clean, dedicated containers; a bucket used for garden compost is a contamination source.
Spawn only once the mix has cooled to room temperature; hot substrate kills spawn.
Do not re-wet dried, opened coir without pasteurising again.
If you add bran, soy hulls or other supplements, sterilise rather than pasteurise.

The EC and pH of raw coir deserve their own article: see coco coir pH and EC management for how to test and correct before you mix a batch.

Reusing spent coir substrate

Spent coir-based substrate has three outlets.

Casing for the next crop. Pardo-Giménez and co-workers showed spent mushroom substrate can go back into production as a casing ingredient, either washed to remove salts or blended with a low-EC material such as coir pith or peat. Blends of 4:1 and 3:2 coir:spent compost gave biological efficiencies of 92.9 and 82.6 kg/100 kg compost (2008), and later work reported values up to 100 kg/kg compost, in line with controls (2010). The limit is EC: the all-spent-compost casing ran at 3140 µS/cm and gave the lowest yield.

Compost and soil improver. This is the common route for small farms. GroCycle describes adding spent blocks to a compost pile or garden bed, with the bonus that oyster mushrooms may fruit again from it. Coir's slow decomposition makes it a long-lasting soil conditioner.

Re-inoculating. Colonised spent substrate can be broken up into a new batch instead of buying spawn. GroCycle warns this raises contamination risk slightly, and it is a poor idea for a commercial grower who sells a consistent product.

What to specify when buying coir for mushrooms

Mushroom growers need a different grade from the drainage-focused material sold for container crops.

Specification	Why it matters for mushrooms
Low EC (washed)	Casing yield fell above about 1.6 dS/m in the Spanish work, and the high-EC coco peat in the Iranian trial failed. Ask for the washed grade and test the EC of a hydrated sample yourself.
Fine pith, few long fibres or chips	A casing needs a fine, even layer that holds water and lets pins push through. Husk chips belong in orchid mixes, not casing.
No added fertiliser, wetting agent or calcium nitrate buffering	Mushroom substrate does not want added nitrogen or soluble salts; buffering with calcium nitrate is a horticultural treatment for plants, not fungi. Washed, unbuffered coir is the right starting point. The difference is explained in buffered vs unbuffered coco peat.
Known compression and expansion	You need to predict how much water a brick or block will take so the hydration water can be measured and heated in one step.
Clean handling and storage	Coir picks up mould spores and insects in damp, open storage. Buy compressed, wrapped material and keep it dry until use.

CVM Fiber and Industries supplies washed, unbuffered coco peat with no calcium nitrate or other chemicals added, in 5 kg blocks for farm-scale batches and 650 g briquettes that match the single-brick recipes above. If you need a particular particle grade for casing or a coir and husk-chip blend for a bulk mix, contact us with your target EC and volume and we will tell you what we can do.

FAQ

Can I grow mushrooms in coco coir alone?

Only a few species fruit well on unsupplemented coir, and even those give modest yields. Research on Pleurotus florida found about 25% bioconversion efficiency on coir pith alone, rising to 110–125% when mixed with rice straw or legume residue. Treat coir as the moisture-holding part of a substrate rather than the food.

What is the CVG ratio for mushroom substrate?

The common recipe is 1 part hydrated coir to 1 part vermiculite by volume with a small amount of gypsum. By weight, supplier recipes for a 650 g brick use 250–300 g of vermiculite, 50–100 g of gypsum and 3.5–3.8 litres of hot water. The exact ratio matters less than hitting field capacity.

Do I need to pasteurise coco coir?

Most growers do, because coir can carry mould spores and insect eggs from storage. Pouring boiling water over a brick in a sealed, insulated bucket and leaving it 6–12 hours both hydrates and pasteurises it. Some suppliers treat pasteurising as optional because coir is low in nutrients, but the cost of skipping it is a lost batch.

What temperature pasteurises coir?

Published hot-water targets range from 65–75 °C held for 1–2 hours up to 82 °C for the same time. Above roughly 82 °C you begin to sterilise rather than pasteurise and lose the helpful bacteria. Measure the centre of the mass, not the water on top, because bulk material takes hours to heat through.

Is coco coir a good casing layer for button mushrooms?

Yes, if it is low in salts and limed. Limed coir pith casing matched or beat sphagnum peat in Spanish trials and was the best of seven materials in an Indian trial. Unlimed, salty coco peat at pH 5.85 and EC 2.99 dS/m performed very poorly in an Iranian trial, so preparation decides the result.

How thick should a coir casing layer be?

For button mushroom compost, research used 3 cm and found 4 cm gave the heaviest mushrooms, with 2 and 6 cm no better than each other. For gourmet species in tubs, a thin 6–12 mm layer applied once primordia are forming is enough.

How much water does a 650 g coir brick take?

Supplier recipes use 3.5 to about 3.8 litres (16 US cups) of boiling water per 650 g brick when making a CVG mix with roughly 250 g to 8 cups of dry vermiculite. The brick expands five to seven times in volume. Adjust by the squeeze test afterwards, since brick weights and moisture vary.

Can spent coir mushroom substrate be reused?

Yes. It can be washed or blended with fresh coir and used as a casing layer for the next button mushroom crop, with research blends of 4:1 coir to spent compost matching peat controls. More commonly it goes to compost or garden beds, where oyster mushrooms sometimes fruit again.

Sources

Pardo, A., de Juan, A. J. and Pardo, J.: Assessment of different casing materials for use as peat alternatives in mushroom cultivation. Evaluation of quantitative and qualitative production parameters. Spanish Journal of Agricultural Research 2(2) (2004)
Pardo-Giménez, A. and Pardo-González, J. E.: Evaluation of casing materials made from spent mushroom substrate and coconut fibre pith for use in production of Agaricus bisporus. Spanish Journal of Agricultural Research 6(4) (2008)
Pardo-Giménez, A., Zied, D. C. and Pardo-González, J. E.: Using spent mushroom substrate as casing layers in new growing cycles. Pesquisa Agropecuária Brasileira 45(10) (2010)
Saini, M., Jarial, R. S. and Jarial, K.: Comparative evaluation of sawdust with different casing materials for the production of Agaricus bisporus under natural bamboo hut conditions. International Journal of Bio-resource and Stress Management 12(5) (2021)
Ghasemi, K., Emadi, M., Bagheri, A. and Mohammadi, M.: Casing material and thickness effects on the yield and nutrient concentration of Agaricus bisporus. Sarhad Journal of Agriculture 36(3) (2020)
Shashirekha, M. N. and Rajarathnam, S.: Bioconversion and biotransformation of coir pith for economic production of Pleurotus florida. World Journal of Microbiology and Biotechnology 23(8) (2007)
Das, D., Kadiruzzaman, M., Adhikary, S., Kabir, M. and Akhtaruzzaman, M.: Yield performance of oyster mushroom (Pleurotus ostreatus) on different substrates. Bangladesh Journal of Agricultural Research 38(4) (2014)
GroCycle: Coco Coir Substrate guide; How to Pasteurize Mushroom Substrate; Mushroom Substrate guide (accessed 2026)
Penn State College of Agricultural Sciences, Mushroom Research Center: Post-crop pasteurization for mushroom farms (accessed 2026)
North Spore: Myco Coco coir substrate and casing layer product guidance (accessed 2026)
La Mycosphère: Compressed coconut fibre block product sheet and CVG recipe (accessed 2026)
Bootstrap Bee: Easy coco coir substrate recipe (accessed 2026)
Zombie Myco: Pasteurize mushroom substrate: is it really necessary? (accessed 2026)
Bhutan Ministry of Economic Affairs: Coir pith block project profile (undated)