Fruiting Chamber Designs
Compare fruiting chamber options from simple to sophisticated. Learn to build SGFCs, monotubs, Martha tents, and dedicated fruiting rooms.
Fruiting Chamber Designs
A fruiting chamber provides the environmental conditions mushrooms need to develop: high humidity, fresh air exchange, proper temperature, and light. This guide covers popular designs from simple to sophisticated.
What Mushrooms Need
| Parameter | Target Range | Purpose |
|---|---|---|
| Humidity | 85-95% | Prevents primordia from drying |
| Fresh air | 4-8 exchanges/hour | Lowers CO2, triggers fruiting |
| Temperature | 55-75°F (species dependent) | Optimal development speed |
| Light | 12 hours indirect | Directional cue for fruiting bodies |
The challenge: fresh air typically lowers humidity. Every fruiting chamber design balances this tradeoff.
Different species, different scales, and different environments need different solutions. Start simple and upgrade based on results.
Design 1: Shotgun Fruiting Chamber (SGFC)
The classic beginner setup using a modified plastic tub.
How It Works
Holes drilled in all six sides allow passive air exchange. Wet perlite on the bottom maintains humidity through evaporation.
Construction
Drill Holes
Drill 1/4" holes every 2 inches across all six sides (including top and bottom).
Raise on Supports
Place tub on four small blocks so air can flow through bottom holes.
Add Perlite
Fill bottom 3-4 inches with soaked perlite. Drain excess water.
Place Substrates
Set cakes or blocks on foil squares above the perlite.
Pros and Cons
| Pros | Cons |
|---|---|
| Very inexpensive ($20) | Passive FAE is inconsistent |
| Simple construction | Humidity varies with climate |
| Good learning tool | Not scalable |
Design 2: Monotub
A larger tub with controlled hole placement for growing bulk substrates.
How It Works
Specific hole placement creates convection: upper holes exhaust CO2-rich air, lower holes draw in fresh air. Polyfill or micropore tape restricts airflow while allowing gas exchange.
Construction
Select Tub
Use a 66-110 quart tub. Larger tubs mean more substrate capacity.
Drill Air Holes
Two 2" holes on each long side, positioned high. Optional: Two 1" holes on each short side, positioned low.
Fill with Polyfill
Stuff holes loosely with polyfill to restrict airflow while maintaining gas exchange.
Add Substrate
Fill bottom 3-4 inches with colonized bulk substrate.
Too much polyfill = insufficient FAE (long stems). Too little = low humidity (aborted pins). Adjust based on results.
Pros and Cons
| Pros | Cons |
|---|---|
| Self-regulating humidity | Requires tuning |
| Minimal daily maintenance | Climate-dependent performance |
| Scalable (multiple tubs) | Limited species suitability |
Design 3: Martha Tent
A greenhouse-style tent with active humidity and FAE control.
How It Works
A plastic shelving unit covered with a plastic tent. An ultrasonic humidifier maintains humidity, and a fan on a timer provides FAE.
Components
| Component | Purpose |
|---|---|
| Wire shelving unit | Structure |
| Clear plastic sheeting | Enclosure |
| Ultrasonic humidifier | Humidity control |
| Hygrometer/thermometer | Monitoring |
| Timer | Automates humidifier/fan cycles |
| Small fan (optional) | Active FAE |
Setup
Assemble Shelving
Set up wire shelving in your fruiting location. 4-5 shelves provides good capacity.
Cover with Plastic
Wrap entire unit with clear plastic, leaving access flaps.
Add Humidifier
Place ultrasonic humidifier inside at bottom. Connect to humidity controller or timer.
Dial In Settings
Start with 4-6 misting cycles per hour. Adjust based on humidity readings.
Ultrasonic humidifiers with tap water deposit minerals. Use distilled water or an evaporative humidifier for cleaner results.
Pros and Cons
| Pros | Cons |
|---|---|
| Consistent conditions | Higher cost ($100-300) |
| Scalable capacity | Requires electricity |
| Works in various climates | More complex setup |
| Visual monitoring easy | Maintenance (water, cleaning) |
Design 4: Dedicated Fruiting Room
For commercial or serious hobby operations, a dedicated room provides maximum control.
Components
| System | Implementation |
|---|---|
| Humidity | Commercial humidifier, fogger, or evaporative cooling |
| FAE | Inline fan with filter, ducted intake/exhaust |
| Temperature | Mini-split AC, heater with thermostat |
| Monitoring | Environmental controller with sensors |
Considerations
- Insulation: Maintain stable temps with minimal energy
- Waterproofing: Walls and floors that handle constant moisture
- Drainage: Floor drain for easy cleaning
- Lighting: Timer-controlled LED strips
Choosing Your Design
| Situation | Recommended Design |
|---|---|
| First grow, learning | SGFC |
| Bulk substrates, hobby scale | Monotub |
| Multiple species, scaling up | Martha Tent |
| Commercial production | Dedicated Room |
Begin with the simplest design that meets your needs. You can always upgrade as you learn what works for your environment and species.
Troubleshooting Common Issues
| Problem | Cause | Solution |
|---|---|---|
| Low humidity | Insufficient humidification | Add misting, increase humidifier output |
| Pooling water | Over-humidification | Reduce output, improve drainage |
| Long stems, tiny caps | High CO2 | Increase FAE |
| Pins aborting | Humidity swings | Stabilize conditions, add automation |
| Mold on surfaces | Stagnant moisture | Improve air circulation |
Quick Reference
| Design | Cost | Capacity | Maintenance | Best For |
|---|---|---|---|---|
| SGFC | $20 | 1-6 cakes | Daily misting | Learning |
| Monotub | $30 | 1 bulk tub | Minimal | Hobby bulk |
| Martha Tent | $100-300 | 4-12 blocks | Daily check | Scaling up |
| Dedicated Room | $500+ | Unlimited | Weekly | Commercial |