The ultimate low-cost fruiting chamber for bulk grows
If you're looking to grow larger yields of mushrooms like Psilocybe cubensis, a monotub is one of the easiest and most effective setups you can build. It’s affordable, scalable, and has been the go-to choice for hobby growers for years.
In this guide, we’ll walk you through building your own monotub step-by-step-no special tools or lab gear required.
🧠 What is a Monotub?
A monotub is a DIY fruiting chamber made from a plastic storage container. It allows your colonised substrate to fruit in a controlled, humid environment—mimicking the conditions mushrooms need to thrive.
Why it works:
- It keeps humidity high
- Allows passive airflow via strategically placed holes
- Is easy to fan or mist when needed
- Can be reused grow after grow
🧰 What You’ll Need
| Item | Description |
|---|---|
| 45–66L clear plastic storage tub | Must be clear or semi-clear for light exposure |
| 6x hole saw or drill with hole bit | 1” and/or 2” circular holes |
| Black plastic liner or bin bag | To block side light and prevent side pins |
| Micropore tape / Polyfill / Filter patches | For covering holes and maintaining gas exchange |
| Spray bottle (for misting) | Optional but helpful |
| Substrate (e.g. CVG) | Coco coir, vermiculite, gypsum |
| Spawn (colonised grain) | Your fully colonised spawn jars or bags |
Pro Tip: Avoid tubs with grooves or ridges on the inside. Smooth walls = better surface for liner and cleaning.
🛠️ Step-by-Step: How to Build Your Monotub
1. Drill Air Exchange Holes
-
Drill four 1” holes just above the substrate line (two on each long side)
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Drill two more holes near the top of the tub (one on each short side)
-
Smooth any sharp edges with sandpaper or a knife
This hole configuration provides passive Fresh Air Exchange (FAE) while keeping humidity high.
2. Line the Tub with a Black Liner
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Cut a black bin bag to size and line the bottom and sides of the tub
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Let the liner sit flush against the walls—no air pockets or creases
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Trim excess from the top edge so it’s just below your lower holes
Why? The liner helps prevent side pins by blocking light and shrinking with the substrate as it consolidates.
3. Add Your Substrate and Spawn
- Mix your colonised grain spawn with bulk substrate (typically CVG) outside the tub
- Then layer it into your tub-ideally 3–4 inches deep
- Level the surface with a spoon or gloved hand
Optional:
-
Add a thin casing layer (extra CVG) over the top
4. Seal the Tub and Add Filters
- Cover each hole with micropore tape, polyfill, or filter patches
- Close the lid and let it incubate at room temperature (21–24°C)
- Avoid opening the tub until full colonisation unless you see contamination
5. Wait for Colonisation (10–14 Days)
- You’ll notice white mycelium creeping across the top
- Once fully colonised, give it another 2–3 days to consolidate before introducing fresh air and misting
If surface looks matted or dry, lightly mist from above.
6. Introduce Fruiting Conditions
- Start fanning the tub 1–2 times per day and mist lightly as needed
- Provide indirect daylight or a 12/12 light cycle
- Maintain 95%+ humidity and fresh air flow to avoid stalling
After 5–10 days, you’ll start to see pinning-baby mushrooms forming.
📸 Optional Add-ons
- Latching lid for better seal
- Thermo/hygrometer stuck inside the tub
- LED light mounted above (6500K daylight bulbs are ideal)
- Second tub stacked on top for a mini greenhouse effect
💡 Final Tips for Monotub Success
- Don’t over-mist—your substrate should glisten, not puddle
- Fan only if condensation disappears or air feels stale
- If you see side pins, make sure your liner is snug and opaque next time
- Clean your tub thoroughly between grows with bleach or ISO
✅ Summary: Monotub Advantages
| ✔️ Easy to build | ✔️ High yields |
|---|---|
| ✔️ Budget-friendly | ✔️ Easy to maintain |
| ✔️ Works for most species | ✔️ Reusable |