What Is CVG Substrate? A Complete Guide

Substrate Guide

CVG — coco coir, vermiculite, and gypsum — is the most popular bulk substrate for home mushroom cultivation. Here's what each ingredient does and how to use it.

Written by the Cloud920 mycologist

Last updated: April 2026

5 min read

CVG stands for coco coir, vermiculite, and gypsum. It's the most widely used bulk substrate for home mushroom cultivation — and for good reason. It holds moisture well, stays airy, and creates the ideal environment for mycelium to colonise and fruit.

If you've seen growers mention CVG on Reddit or in grow guides, this is what they're talking about. Here's everything you need to know.

What Each Ingredient Does

C — Coco Coir

Fibrous coconut husk material. Holds moisture exceptionally well while staying light and airy. Naturally resistant to mould — which helps keep contamination at bay.

V — Vermiculite

Expanded mineral that improves air circulation and drainage. Keeps the substrate from compacting too tightly, which would restrict oxygen flow to your mycelium.

G — Gypsum

Calcium sulphate that balances the pH and prevents the substrate from clumping. A small amount goes a long way — keeps the texture loose and workable.

Together, the three create a substrate with the right balance of moisture, aeration, and pH for strong, even mycelium colonisation and healthy fruiting.

CVG vs Grain Spawn: What's the Difference?

This is a common point of confusion for new growers. Think of it this way: grain spawn is the starter, CVG is the main course.

	Grain Spawn (Millet / Corn)	CVG Substrate
Purpose	Colonise mycelium	Fruit mushrooms
When you use it	First — inoculate here	Second — mix spawn into this
Inoculation	Inject liquid culture or spores	No — receives colonised grain
End result	Colonised grain (spawn)	Fruiting block

How to Use CVG Substrate

Option 1 — Two-bag method (recommended)

Most common

1
Inoculate your grain bag — inject liquid culture or spores through the injection port

2
Wait for full colonisation — 2–4 weeks depending on grain type and temperature

3
Mix spawn into CVG — break up the colonised grain and mix into your CVG bag at roughly 1 part grain to 2–3 parts CVG

4
Wait for colonisation — mycelium spreads from grain into CVG over 1–2 weeks

5
Fruit — once fully colonised, introduce fruiting conditions (fresh air, light, humidity) and harvest

Option 2 — Direct inoculation into CVG

You can inoculate CVG directly with liquid culture, skipping the grain bag step. This works, but colonisation is slower and less even than using grain spawn. Most growers use the two-bag method for better results.

Option 3 — Pre-sterilised CVG bag (the easy way)

Our pre-sterilised CVG substrate bags come ready to use — hydrated to the right field capacity, sterilised, and sealed. You just add your colonised grain spawn or liquid culture and go.

What Species Grow Well on CVG?

Works great

Psilocybe cubensis varieties
Oyster mushrooms, button mushrooms
Turkey tail and some reishi preparations

Not ideal

P. azurescens, P. cyanescens
King oyster, lion's mane
These need a hardwood-based substrate to thrive.

The Right Moisture Level

The biggest mistake new growers make with CVG is getting the moisture level wrong. Too wet and the substrate becomes anaerobic — a breeding ground for contamination. Too dry and mycelium won't colonise properly.

The squeeze test: Grab a handful of CVG and squeeze it in your fist. A few drops should come out — that's the right moisture level. A stream means too wet. Nothing means too dry.

If you're using our pre-sterilised CVG bags, this is already handled for you — every bag is hydrated to the correct field capacity before it's sealed.

Frequently Asked Questions

CVG made with coco coir is naturally resistant enough that many growers pasteurise rather than fully sterilise it. That said, a pre-sterilised bag removes the risk entirely — no equipment, no guesswork. Our CVG substrate bags are fully sterilised and ready to use.

A common ratio is 1 part colonised grain to 2–3 parts CVG by volume. More spawn speeds up colonisation. Some growers go as high as 1:1 for very fast results.

Not recommended. After a full grow cycle the substrate is depleted and more vulnerable to contamination. Starting with fresh substrate each grow gives you the best results and the cleanest environment.

Typically 7–14 days at 21–26°C. You'll see white mycelium spreading through the substrate. Once the surface is fully white, it's ready to fruit.

Yes — you can inoculate CVG directly with liquid culture. It works, but colonisation is slower and patchier than using grain spawn first. The two-bag method consistently produces better results.

Field capacity is the moisture level at which a substrate holds as much water as possible without excess runoff — like soil after rainfall has drained away. It's the sweet point for mushroom cultivation: wet enough for mycelium to thrive, dry enough to prevent anaerobic conditions.

Ready to grow?

Pre-sterilised CVG. No prep needed.

Hydrated to field capacity, sterilised, tested, and sealed with an injection port. Ships fast across Europe from the Netherlands.

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