Coconut coir is the fibrous husk that is left over when a coconut is processed, compressed into bricks and shipped around the world as a growing medium. For mushroom growers it is close to perfect bulk material: it holds several times its weight in water, it has an open structure that lets air through, it contains so little nutrition that contaminants are not interested in it, and it is cheap. Add vermiculite and a little mineral nutrition and you have CVA, the substrate most hobby oyster grows in Australia run on.

What each ingredient does

Coco coir

Structure and water. It is the body of the substrate and the reservoir the mushrooms draw on during a flush.

Vermiculite

Air and buffering. The puffed mineral keeps the mix from compacting, holds extra water and releases it slowly, and keeps pH stable.

Minerals (the A)

Trace nutrition and calcium that help the mycelium build dense, healthy tissue. Our recipe has been refined over years of grows for consistent results.

Who it suits

Oyster mushrooms of every colour are the natural match: pink, blue, pearl and phoenix all colonise coir fast and fruit heavily on it. It also suits species that like a compost-style base, and for those growers who want more nutrition in the mix we make CVWA, the same base with worm castings and Azomite. Wood lovers (lion's mane, shiitake, king oyster, reishi) will grow on coir but fruit far better on hardwood.

Running a coir tub, step by step

1. Pick a tub

   A clear 50 to 60 litre storage tub with a lid takes a 5kg bag of CVA at 8 to 12cm deep. Wipe it inside with 70% alcohol.

2. Spawn

   In a still air box or in front of a flow hood, tip the substrate in, scatter the broken-up grain spawn over it at 1:2 to 1:4 by weight, and fold it through with gloved hands until no clumps remain. Flatten the surface and press it gently.

3. Colonise

   Lid on, into the dark at 20 to 24°C. Oysters will have the surface white in 5 to 10 days at 1:2. Do not open it to look; watch through the side.

4. Introduce fruiting conditions

   When the surface is fully white, open the tub. Mist the walls (not the surface) to keep humidity up, give it fresh air several times a day or crack the lid, and provide indirect light.

5. Harvest and repeat

   Pins in a few days, harvest about a week later. Rest, soak if the block feels light, and fruit again. Fruiting guide.

Depth, surface and air

Deeper is not better. A 6 to 12cm layer gives the mycelium enough reserve for two or three flushes while leaving the whole mass oxygenated; 20cm tubs go anaerobic at the bottom and stall. A flat, lightly pressed surface pins evenly. And oysters need a great deal of fresh air once they pin: long, thin stems and tiny caps mean CO2 is building up, so open the lid more often.

Making your own vs buying it

People do mix their own coir substrate: a coir brick, a few litres of boiling water, vermiculite and a mineral pinch in a bucket, then an hour or two to pasteurise and cool. It works for plain coir. It does not work well for an enriched recipe, which needs a real sterilisation cycle, and it is messy, slow and inconsistent. A sealed bag at field capacity with the recipe already dialled in is what lets you spend your weekend on the mushrooms.

Written by the Aus Myco Kingdom crew. Everything here is general growing information for gourmet and medicinal species; your room, your climate and your culture will have the final say.