How to Prepare Coco Coir and Vermiculite for Mushroom Growing
GROWING
3/7/20254 min read
How to Prepare Coco Coir and Vermiculite for Mushroom Growing
If you're looking for a simple, reliable bulk substrate for growing gourmet mushrooms, a coco coir and vermiculite mix is one of the best places to start. It's inexpensive, easy to make, and doesn't require a pressure cooker or complicated equipment.
I've been using this recipe for years, and it's still the one I come back to most often. I've experimented with other substrates, including hardwood mixes, straw, and even manure, but for home growing I keep choosing coco coir because it's simple, clean, and easy to get.
If you're growing oyster mushrooms, Pioppino, or other gourmet species that grow well on coco coir, this recipe is a great place to start.
Why I Use Coco Coir Instead of Other Substrates
One of the biggest reasons I use coco coir is convenience.
Hardwood substrates like Master's Mix work great, but I have to order large bags online. Living in an apartment, I never liked having giant bags labeled "mushroom substrate" sitting outside my door waiting to be picked up.
Coco coir bricks are much easier to buy. I can order a pack online, store them in a closet, and grab one whenever I need to make substrate.
I've also tried straw and manure-based substrates. They both work, but I found them much messier to prepare. For my growing setup, coco coir and vermiculite are much easier to work with.
What You'll Need
4 quarts (16 cups) boiling water
5-gallon bucket with a lid
Kitchen knife (to break up the brick)
Large spoon or paint stirrer (for mixing)
Optional:
1 tablespoon gypsum (some growers like to add it, but I usually don't.)
Step 1: Break Up the Coco Coir Brick
Take one 650-gram coco coir brick and use a kitchen knife to break it into smaller pieces. Put the pieces into a clean 5-gallon bucket.
I always break the brick up first because I've found it hydrates more evenly and is less likely to leave dry clumps in the middle.
I used to buy one large coco coir block because it was a little cheaper, but I got tired of cutting pieces off and weighing them every time I made substrate. Now I just buy the standard 650-gram bricks. They cost a little more, but they're much more convenient and the recipe comes out the same every time.
Step 2: Add the Vermiculite
Add 2 quarts (8 cups) of vermiculite to the bucket.
If you're just getting started, a small bag is fine. If you plan on growing mushrooms regularly, buying vermiculite in bulk will usually save money over time.
Step 3: Add the Boiling Water
Bring 4 quarts (16 cups) of water to a rolling boil and carefully pour it into the bucket. Put the lid on and let it sit for about one hour.
After an hour, remove the lid and stir everything well. Put the lid back on and let it sit for another hour before giving it one final stir.
To be honest, I've only stirred it once plenty of times and still had good results. I just think stirring it twice helps make sure there aren't any dry clumps left.
Step 4: Let It Cool
Leave the substrate until it has completely cooled before adding your grain spawn.
If I make substrate in the morning, it's usually cool enough to use that evening. If I'm not in a hurry, I'll just leave it overnight and use it the next day.
One mistake I made when I first started was trying to spawn while the substrate was still warm. Always wait until it's cool, or you can damage the mycelium.
Why I Buy the Small Bricks
When I first started growing mushrooms, I bought one large compressed coco coir block because it saved a little money.
Eventually I realized I was spending extra time cutting pieces off and weighing them every time I wanted to make substrate.
I also tried loose coco coir, but it was easier to accidentally use a little too much or too little.
Now I simply buy the standard 650-gram bricks. I know the recipe works every time, and it's worth the small extra cost to save time.
Common Mistakes
Probably the biggest mistake I made when I first started was not mixing the bucket well enough. Everything looked hydrated from the top, but when I came back later I'd find dry chunks of coco coir hiding in the middle.
Another common mistake is adding grain spawn before the substrate has completely cooled. It can be tempting to hurry, but always wait until it's cool to the touch before spawning.
Using too much water is another easy mistake. If your substrate feels soggy instead of just damp, take a look at my guide on how to tell if mushroom substrate is too wet before adding your spawn.
If you're unsure whether your substrate has the right amount of moisture, check out my guide on How to Tell if Mushroom Substrate Is Too Wet.
What Mushrooms Does This Recipe Work For?
I've had great success using this recipe with oyster mushrooms and Pioppino.
For species like Lion's Mane, however, I usually switch to a hardwood-based substrate. While Lion's Mane will sometimes grow on coco coir, I've consistently had better results using supplemented hardwood sawdust.
Disclosure: As an Amazon Associate, I earn from qualifying purchases. If you buy through the links on this page, I may earn a small commission at no additional cost to you.
Final Thoughts
I've tried a lot of different substrate recipes over the years, but this is still the one I recommend to most beginners.
It's inexpensive, easy to make, and once you've prepared it a few times, the whole process becomes second nature.
If you're just getting started, I'd focus on learning one reliable recipe like this before experimenting with more advanced substrates.
