Coco coir has become the gold standard bulk substrate for mushroom cultivation. It’s contamination-resistant, holds moisture perfectly, and provides an ideal structure for mycelium colonization. This guide covers the classic CVG (Coir, Vermiculite, Gypsum) recipe that consistently produces excellent results.

Why Coco Coir?

Coco coir offers unique advantages:

• Naturally resistant to contamination (antifungal properties)
• Perfect structure for gas exchange
• Excellent moisture retention without becoming anaerobic
• Nutritionally inert (prevents contamination growth)
• Sustainable and renewable resource
• Consistent quality between batches

Understanding Field Capacity

Field capacity is the maximum amount of water substrate can hold while still maintaining air pockets. This is crucial for healthy mycelium growth.

The Squeeze Test

1. Grab a handful of substrate
2. Squeeze firmly
3. Perfect: 1-2 drops fall
4. Too wet: Stream of water
5. Too dry: No drops at all

Basic Coir Recipe (Coir Only)

The simplest approach for beginners:

Ingredients (for 1 brick)

• 650g coco coir brick
• 4 quarts boiling water

Process

1. Place coir brick in 5-gallon bucket
2. Pour boiling water over brick
3. Cover with lid immediately
4. Wait 1 hour for hydration
5. Break apart with hands or fork
6. Mix thoroughly ensuring even hydration

CVG Recipe (Recommended)

Adding vermiculite and gypsum improves performance:

Ingredients

• 650g coco coir brick
• 8 cups coarse vermiculite
• 1 cup gypsum
• 4.5 quarts boiling water

Benefits of Additions

• Vermiculite: Increases moisture retention and provides structure
• Gypsum: Buffers pH, adds calcium, prevents clumping

Mixing Process

1. Prepare coir: Break brick into chunks in bucket
2. Add vermiculite: Spread evenly over coir
3. Add gypsum: Sprinkle over mixture
4. Pour boiling water: Add slowly while stirring
5. Mix thoroughly: Ensure even distribution
6. Cover and wait: 1-2 hours for full hydration
7. Final mix: Break up any clumps

Pasteurization Methods

Bucket Tek (Easiest)

The boiling water provides sufficient pasteurization:

1. Water temperature must be 170°F minimum
2. Keep covered to maintain heat
3. Allow to cool to room temperature (4-8 hours)

Oven Pasteurization (Alternative)

For extra insurance:

1. Hydrate substrate to field capacity
2. Place in aluminum pans
3. Cover with foil
4. Bake at 180°F for 2 hours
5. Cool completely before use

Pressure Cooker (Overkill)

Not necessary but some prefer it:

1. Bag substrate in autoclave bags
2. Sterilize at 15 PSI for 2.5 hours
3. Cool completely in bags

Achieving Perfect Field Capacity

Initial Hydration

Start with less water than you think:

• Coir only: 3.5-4 quarts per brick
• CVG: 4-4.5 quarts per brick
• Climate matters: Dry climates need more water

Fine-Tuning

1. Test after cooling: Substrate shrinks when cool
2. Add water gradually: 1 cup at a time if needed
3. Mix thoroughly: Between additions
4. Retest frequently: Until perfect

Common Mistakes

• Over-hydration: Leading cause of contamination
• Under-mixing: Creates dry pockets
• Rushing: Not allowing full absorption time
• Wrong coir type: Avoid fine powder coir

Spawn to Substrate Ratios

Once your substrate is ready:

Conservative (1:4)

• 1 part spawn to 4 parts substrate
• Slower colonization (14-21 days)
• Lower contamination risk

Standard (1:3)

• 1 part spawn to 3 parts substrate
• Balanced speed and safety (10-14 days)
• Most commonly used

Aggressive (1:2)

• 1 part spawn to 2 parts substrate
• Fast colonization (7-10 days)
• Higher spawn cost

Storage and Shelf Life

Fresh Substrate

• Use within 24 hours for best results
• Can store 3-5 days refrigerated
• Signs of fermentation: sour smell, heat

Pre-made Substrate

• Seal in bags after cooling
• Store in cool, dark place
• Use within 1 week
• Freeze for longer storage (up to 3 months)

Troubleshooting

Substrate Too Wet

Problem: Water pooling, anaerobic smell Solution: Add dry vermiculite, increase air exchange

Substrate Too Dry

Problem: Slow colonization, stalling Solution: Mist surface lightly, maintain humidity

Contamination Issues

Problem: Green mold, bacteria Causes:

• Over-hydration
• Insufficient pasteurization
• Contaminated spawn
• Poor sterile technique

Slow Colonization

Causes:

• Temperature too low (needs 75-80°F)
• Incorrect moisture content
• Old or weak spawn
• Poor spawn distribution

Recipe Variations

Coffee Coir Mix

Add spent coffee grounds for extra nutrition:

• 650g coir
• 2 cups coffee grounds (fresh)
• 8 cups vermiculite
• 1 cup gypsum

Straw-Coir Blend

For oyster mushrooms:

• 325g coir (half brick)
• 5 cups chopped straw
• 6 cups vermiculite
• No gypsum needed

Manure-Coir Mix

Advanced recipe:

• 650g coir
• 5 cups aged horse manure
• 5 cups vermiculite
• 2 cups gypsum

Tips for Success

1. Quality matters: Use plain coir (no additives)
2. Measure carefully: Consistency improves results
3. Document ratios: Find your perfect recipe
4. Work clean: Contamination prevention is key
5. Be patient: Don’t rush the process

Scaling Up

For larger operations:

• Concrete mixer: For bulk preparation
• Drum pasteurizer: Steam pasteurization
• Moisture meter: Precise field capacity
• pH meter: Monitor substrate pH (6.5-7.5 ideal)

Conclusion

Mastering coco coir substrate preparation is fundamental to successful bulk cultivation. The CVG recipe provides an excellent balance of moisture retention, structure, and contamination resistance. With practice, you’ll develop an intuitive feel for perfect field capacity - the key to consistent, abundant harvests.

Remember: substrate preparation is where many grows succeed or fail. Take your time, follow the recipe, and always prioritize proper moisture content over speed. Your mushrooms will reward you with vigorous colonization and impressive yields.