The Ultimate CVG Mushroom Substrate Guide: How to Make Mushroom Substrate
6 MIN READ
Your substrate can make or break a mushroom grow. If it's off, you'll end up with weak colonization, contamination, or no mushrooms at all, so it's worth getting right before anything else.
CVG is the substrate I rely on, and it's a great starting point if you're new to growing. It's cheap, forgiving and easy to make at home.
This guide covers what CVG is, which ingredients to buy, a CVG substrate recipe you can copy, how to get the moisture right, and what to do when something goes wrong.
Rather watch than read? I walk through the whole process in this CVG substrate video. And if you want a recipe for your own batch size, use our CVG Substrate Calculator.
What is CVG Substrate?
CVG stands for coco coir, vermiculite and gypsum. Together, these three ingredients make a bulk substrate that you mix with colonized grain spawn, and each one does a different job:
- Coco coir is the base. It soaks up and holds a lot of water, but it doesn't offer much nutrition on its own.
- Vermiculite holds water too, and it also keeps the mix airy. That airflow lets the mycelium breathe and exchange gases.
- Gypsum supplies calcium and sulfur. It also acts as a pH buffer, neutralizing the acidic waste the mycelium produces as it grows.
You'll sometimes hear that gypsum is optional. Maybe, but I've never regretted adding it, and I've always seen a difference.
Choosing Your CVG Ingredients
What you buy matters more than you'd think. A poor choice at the shop can quietly ruin the whole batch, so here's what I look for.
Coco coir: My pick is reptile-grade coir, because it usually has fewer chemical residues and less salt, and both can slow mycelium down. Garden coir works as well, but it's more likely to carry a higher spore load. Either way, go for coir that has been washed and heat treated.
Vermiculite: Medium grade is the sweet spot. It gives you good airflow while still holding moisture. Large grade is fine too. I'd avoid small grade, since it tends to clump the substrate together.
Gypsum: Buy garden gypsum and keep plaster gypsum far away from your kitchen. Plaster gypsum often contains additives you don't want near your mushrooms, and it makes the substrate clump.
How to Calculate Your CVG Substrate Recipe?
Before mixing anything, figure out how much substrate you need. Our CVG Substrate Calculator handles that, and you can use it two ways.
The simple version is the quickest: pick your units, type in how much substrate you want, add your ingredients and press calculate. Use it when you already know your target volume.
The advanced version works backwards from your spawn. Say you have 1 liter of colonized grain. You choose a grain-to-substrate ratio (I like a balanced 1:3), add your ingredients, and the calculator returns a recipe tuned for the right moisture level.
How to Make CVG Substrate?
This is the CVG substrate recipe I use for 5 liters of finished substrate:
| Recipe for 5L CVG | |
|---|---|
| Ingredients | Amount |
| Coco Coir | 300g |
| Vermiculite | 80g |
| Gypsum | 50g |
| Water | 1.8 liters |
Step by Step Guide
- Boil the water. Use unchlorinated water if you can, since chlorine can stress the mycelium.
- Fill the bucket. Add the coir, vermiculite and gypsum. There's no need to layer them, because you'll mix everything later anyway.
- Add the boiling water and close the lid. Steam builds up and can warp a plastic bucket, so let some out now and then. A towel wrapped around the bucket helps hold the heat, but it's optional.
- Let it sit for 4 to 6 hours. I usually do this overnight so there's no waiting around the next day.
- Mix it up. Once it's cool, put on gloves and mix thoroughly. Vermiculite and gypsum like to settle at the bottom, so scrape the bucket as you go.
-
Check the moisture using the field capacity test below.
What you just did is called pasteurization. It isn't the same as sterilization, but it's all CVG needs (more on that further down).
- Tip: Use a bigger bucket than you think you need. Mine was a bit too small the first time, and I spilled a fair amount while mixing. A pressure cooker works too if you have one.
What is Field Capacity?
Field capacity is the ideal moisture level for your substrate, enough water to feed the whole grow without any misting.
The easy way to check is to grab a handful and squeeze it hard. If a few drops come out, you're there.
| Substrate | Squeezing |
|---|---|
| Too dry | Nothing comes out |
| Perfect | Just a couple of drops |
| Too wet | Substrate is soaking wet |
How to Fix CVG Substrate That's Too Dry or Too Wet
No need to bin the batch. Both problems are easy to correct.
- Too dry: Mix in hot water a little at a time until it reaches field capacity. This can take a while, so add some, mix, and test again.
- Too wet: Squeeze out the extra water bit by bit until a handful gives just a few drops.
How to Use CVG Substrate
Once your substrate is at field capacity, it's time to combine it with spawn.
- Pick your ratio. I mix grain spawn and substrate by volume at 1:1 or 1:2. That colonizes quickly and gives bigger yields. Lower ratios colonize more slowly and leave more room for contamination.
- Combine and mix. Add the grain spawn and most of your substrate (hold some back) and mix well.
- Press it down gently.
- Add a casing layer. Spread the leftover substrate on top, about 0.5 cm thick. It protects the mycelium from drying out and can help prevent side pinning.
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Compress it again, and you're done.
Pasteurization vs. Sterilization: Why Pasteurized CVG Works
Sterilization wipes out everything: bacteria, spores, all microorganisms. Pasteurization is gentler. It reduces mold spores and leaves some beneficial organisms alive. So why does pasteurizing do the job for CVG?
- It softens the fibers. Killing some mold spores is a nice side effect, but the real benefit is that hot water softens the coco coir, so the mycelium can break it down and colonize it more easily.
- There's little food for contaminants. Coco coir is mostly plant fiber and lacks the sugars and carbohydrates that mold and bacteria feed on. Mycelium can slowly digest the fibers and turn them into nutrition.
- The substrate usually isn't the culprit. In my experience contamination mostly comes from poor grain spawn or weak cultures, not from the CVG itself.
How to Store CVG Substrate
I normally mix a batch right before spawning to a monotub. If you have leftovers, though, they keep well as long as they don't dry out. Some growers report using CVG that was over a year old without any problems.
I wanted to see this for myself, so I left a batch in an airtight bucket for a month. The surface had dried a little, but underneath it was still at perfect field capacity, and a quick mix was all it needed.
Premade CVG bags behave the same way. They last a long time, but they can dry out too, so try to use them within the first 4 weeks.
Conclusion
That's everything you need to make and use CVG substrate: the right ingredients, a reliable ratio, the squeeze test for moisture, and a little patience. Get those right and you're already ahead of most beginners.
If you want to see it in action, watch the full video and browse our other grow guides. And if you'd like to chat with other growers, come join our Discord, where we run free giveaways and share exclusive content.
Frequently Asked Questions
How Do I Know If My Cvg Has The Right Moisture?▼
Squeeze a handful as hard as you can, and a few drops should come out. That is field capacity. If nothing drips, the substrate is too dry. If water runs out, it is too wet. Hit it right and you will not need to mist during the grow. Fix a bad batch with hot water or by squeezing out the excess.
Do I Need To Sterilize Cvg Substrate?▼
No, pasteurizing is enough for CVG. Hot water softens the coco coir fibers so the mycelium can colonize them more easily, and coir has very few of the sugars that mold and bacteria feed on. In my experience, contamination usually comes from poor grain spawn or weak cultures, not from the substrate.
Can I Make Cvg Without Gypsum?▼
Yes, you can skip it, but I wouldn't. Gypsum adds calcium and sulfur and works as a pH buffer, neutralizing the acidic waste the mycelium produces. Some growers get by without it, yet I have always seen a difference when I add it. It costs very little compared to the rest of your grow.
How Long Does Cvg Last?▼
CVG keeps for a long time in an airtight bucket as long as it does not dry out. Some growers report using batches that were over a year old. I left mine for a month and it was still at field capacity under a dry-looking surface. Premade bags can dry out too, so use them within 4 weeks.
What Grain-to-substrate Ratio Should I Use?▼
I use 1:1 or 1:2 grain to substrate by volume. Both colonize quickly and tend to give bigger yields. Smaller ratios, with less grain for the same amount of substrate, colonize much more slowly, which gives contamination more time to take hold. Clean, healthy spawn matters just as much.