Tutorials/Substrate/Coir and CVG

Bulk substrate is the material your mushrooms actually fruit from. It's less nutritious than grain on purpose: it gives the mycelium water and structure while making it harder for contaminants to compete. Because of that, bulk only needs to be pasteurized, which kills most competitors while leaving harmless microbes that help defend it.

Coir-based substrates are the easiest place to start. They're cheap, clean, consistent, and hard to mess up.

Ingredients

• Coco coir: shredded coconut husk, sold as compressed bricks (often 650 g). It holds water well and resists contamination.
• Vermiculite: a puffed mineral that holds water and keeps the mix airy. Use horticultural grade.
• Gypsum: calcium sulfate. Adds calcium and sulfur and helps keep the mix from compacting.

CVG stands for Coir, Vermiculite, Gypsum.

Recipes

Recipe card for coir and CVG, from Philly Golden Teacher

Recipe	Coir	Vermiculite	Gypsum	Water
Coir only	1 brick (650 g)	–	–	3.5 qt (14 cups)
CVG	1 brick (650 g)	2 qt (8 cups)	1 cup	4.5 qt (18 cups)

One brick of CVG makes about 11 lb of hydrated substrate, enough for a typical 54–66 qt monotub with 2–3 quarts of spawn.

These water amounts are for dry, compressed bricks. Loose bags of "coco coir potting mix" often come partly hydrated already. Start with roughly half the water and add more only if needed.

Bucket tek: pasteurize and hydrate in one step

1. Break up the coir brick and add it with the vermiculite and gypsum to a 5-gallon bucket with a lid. An insulated cooler or 5-gallon Igloo drink cooler works even better because it holds heat longer.
2. Bring the water to a full boil and pour it over the dry ingredients.
3. Seal the lid immediately.
4. Leave it closed. The goal is to keep it above about 150–170°F for at least 2 hours. A cooler will do this on its own; a plain bucket can be wrapped in towels or a blanket.
5. Let it sit until it's cooled to room temperature, usually overnight. Give it at least 6 hours so the coir fully absorbs the water.
6. Break up any clumps with clean, gloved hands before mixing with spawn.

At Colorado Springs elevations water boils at about 201°F instead of 212°F, which is still well above pasteurization temperature. The bucket tek doesn't need any altitude adjustment.

Field capacity

Substrate should be at field capacity: holding as much water as it can without any pooling. The test:

• Grab a handful and squeeze hard.
• Just right: a few drops run out, and it holds together loosely when you open your hand.
• Too wet: a stream of water runs out. Excess water invites bacteria.
• Too dry: nothing comes out and it crumbles. Mushrooms are mostly water, so dry substrate means small flushes.

Fixing soupy substrate

If the mix still looks like soup a couple of hours in:

• Stir in about 2 cups of dry coir and 1 cup of vermiculite, wait 30 minutes, and check again.
• Keeping it hot (a pot on low heat, steaming) speeds absorption and drives off a bit of the extra water.
• Draining it through a clean pillowcase or mesh bag and wringing it out also works.

Spawning

Mix colonized grain spawn into the substrate at somewhere between 1:1 and 1:4 spawn to substrate by volume. More spawn colonizes faster and resists contamination better. Then follow monotub fruiting.

Sources

• Philly Golden Teacher, Bucket tek substrate video (YouTube): the recipe card above
• Notes on loose coir, soaking time, and fixing over-wet substrate contributed by league members.