Substrates and casing

CVGCVGA common bulk substrate of coconut coir, vermiculite and a little gypsum, hydrated with hot water. is coconut coir, vermiculite and gypsum. It holds water well, has almost no food in it, and is easy to make clean. Coir sold as compressed bricks is the usual choice.

By volume

About 2 parts coir to 1 part vermiculite, plus a little gypsum (roughly 5%)

One common batch

One 650 g coir brick, about 2 quarts vermiculite, about a cup of gypsum

Water

Roughly 4–4.5 quarts boiling water for that batch; add slowly and check

Result

About 8–9 quarts hydrated substrate

A widely used method on Shroomery pours boiling water over the dry mix in a bucket or insulated cooler, lids it and leaves it overnight. The trapped heat holds it hot enough for hours. Because coir has so little food, plenty of growers argue it barely needs pasteurizing at all, but the hot-water soak is cheap insurance.

Aged horse manure is richer and can give heavier flushes, at the cost of more contamination risk. It must be fully dry and aged, crumbling with no ammonia smell; fresh manure has too much ammonia (Bible, p. 178–181). The Bible's own recipe is 12 parts dry manure to 6 parts vermiculite and 1 part gypsum, by volume (p. 188–189). Additions like coffee grounds or worm castings add food, and the richer the mix, the higher the risk (p. 184–185).

Field capacityField capacityHolding as much water as a substrate can without dripping; squeezed hard, it gives a few drops, not a stream. means holding all the water it can without dripping. Test it by hand (Bible, p. 188–189):

• Held loosely, nothing drips.
• Squeezed gently, a few drops.
• Squeezed hard, a short trickle that stops within a few seconds.

Too wet invites bacteria and pooling; too dry stalls colonization and pins. Add water slowly and test often. If you overshoot, mix in more dry coir or vermiculite.

Grain needs sterilizationSterilizationKilling everything living in grain or substrate with steam at 15 psi (250 °F) in a pressure cooker: about 20 minutes for small PF jars, hours for big grain loads. in a pressure cooker because it is rich food. Bulk substrate only needs pasteurizationPasteurizationHolding substrate hot, around 160–180 °F (71–82 °C) for an hour or more, to knock back competitors without sterilizing it.: holding it hot enough to knock back competitors while leaving some harmless microbes alive. The Bible holds a pillowcase of substrate in a water bath at about 176 °F (80 °C) for an hour, then lets it drain overnight to field capacity (p. 197–199). Let it cool to room temperature before spawning.

A casing layerCasing layerA thin, water-holding top layer with no food in it, spread over colonized substrate to keep the fruiting surface evenly moist. is a thin layer with no food in it, spread over fully colonized bulk. It holds water, keeps the surface evenly moist and gives pins a protected place to form. A peer-reviewed comparison of cased and uncased cubensis measured far higher yields on cased beds, while the Bible's authors skip casing and saw no yield gain in their own tests (p. 191, 204, 206). It is most useful when you cannot keep the surface humid otherwise.

Simple mix

Coir and vermiculite, roughly half and half, at field capacity

Peat-based (classic)

10 parts peat, 1 part gypsum, 1 part calcium carbonate (Bible, p. 206)

Thickness

About a quarter of the substrate depth: 3/4 inch over 3 inches (Bible, p. 192)

When

After the bulk is fully colonized, not at spawning

Hydration

At or very slightly wetter than field capacity

Casing has to be clean too: pasteurize it the same way as bulk (Bible, p. 207–210). Spread it gently, do not pack it, and keep the colonized bulk underneath intact.