How to Prepare Coco Coir and Vermiculite for Mushroom Growing

If you’re looking for a reliable, beginner-friendly bulk substrate for growing gourmet mushrooms, a coco coir and vermiculite mix is one of the best options. It’s widely used because it holds moisture well, resists contamination, and is easy to prepare with minimal equipment.

I’ve been using this recipe for over five years, and it continues to be one of the most effective methods for successful mushroom cultivation.

Why Use Coco Coir and Vermiculite?

✅ Coco coir – A natural fiber from coconut husks that retains moisture, resists mold, and provides a great growing environment for mycelium.
✅ Vermiculite – A lightweight mineral that improves water retention and aeration.
✅ Together, they create an ideal substrate for colonization and fruiting.

What You’ll Need:

• 1 brick of coco coir (650g)

• 2 quarts of vermiculite

• 4 quarts of boiling water

• 5-gallon bucket with a lid

• (Optional) 1 tablespoon of gypsum – Adds calcium and sulfur to support mycelium growth.

Step-by-Step Guide:

1. Break Up the Coco Coir

Place the coco coir brick into your 5-gallon bucket. Breaking it into smaller chunks helps it hydrate more evenly.

2. Add Vermiculite

Pour 2 quarts of vermiculite into the bucket with the coir.

3. Boil Water & Hydrate the Mix

• Heat 4 quarts of water until boiling.

• Slowly pour the boiling water over the coir and vermiculite mixture. Stir as you go to ensure even absorption.

4. Let It Sit & Pasteurize

• Close the lid on the bucket and let the mixture sit for at least 1 hour. The heat will naturally pasteurize the substrate, reducing contamination risk.

• After an hour, stir the mix with a large spoon, breaking up any clumps to ensure even consistency.

5. Check Moisture Content

• After cooling for 3–4 hours, fluff up the substrate with your hands.

• Do the squeeze test: Grab a handful and squeeze—only a few drops of water should come out. If it’s too wet, let it air out before use.

Using the Substrate

Once fully cooled, your coco coir and vermiculite mix is ready for spawning. You can mix it with grain spawn in a monotub, dub tub, or grow bags.

This substrate works well for species like oyster mushrooms, Pioppino, and other gourmet varieties. However, Lion’s Mane prefers a more wood-based substrate, so this method may not be ideal for that species.

Final Tips for Success

✅ Use high-quality, low-salt coco coir (some brands are buffered with salt, which can harm mycelium).
✅ Always pasteurize properly to minimize contamination risk.
✅ Keep your substrate at field capacity—not too wet or too dry.

This method is simple, scalable, and one of the best ways to grow mushrooms at home. If you found this guide helpful, check out my TikTok video for a quick visual breakdown of the process!