Growing Mushrooms in a Monotub: The Ultimate FAQ Guide
Everything you need to know about monotub cultivation, from setup to harvest!
🌱 Monotubs are a popular method for growing mushrooms at scale, offering a controlled environment for optimal yields. Below, we answer the 28 most common questions about monotub cultivation. Click any question to jump to its answer, or read through for a full Growing Mushrooms in a Monotub guide!
Table of Contents
- What substrate recipe is best for monotubs?
- How do I properly prepare and pasteurize substrate?
- What’s the ideal spawn-to-substrate ratio?
- Do I need a casing layer, and if so, how do I apply it?
- How do I set up a monotub (e.g., hole placement, size, liner use)?
- What’s the ideal temperature and humidity for colonization and fruiting?
- How much light do mushrooms need in a monotub?
- How to manage fresh air exchange (FAE) in a monotub?
- How do I prevent contamination in my monotub?
- What are the signs of contamination (e.g., mold, bacteria)?
- Can I save a contaminated monotub, or should I discard it?
- How long does colonization take before fruiting?
- When should I introduce fruiting conditions?
- Why aren’t pins or mushrooms forming (causes and fixes)?
- How often should I mist and fan the monotub?
- When and how do I harvest mushrooms without harming the mycelium?
- How do I rehydrate the substrate for additional flushes?
- What do I do after the final flush (e.g., disposing of substrate)?
- What causes overlay/stroma, and how do I fix it?
- Why are my mushrooms small, thin, or deformed?
- Why is my substrate drying out or too wet?
- Can I reuse substrate or monotub materials?
- How can I maximize yields in a monotub?
- What common mistakes should I avoid as a beginner?
- How many flushes can I expect from one monotub?
- Are monotubs suitable for all mushroom species, or just specific ones?
- How do I store harvested mushrooms from a monotub?
- Do I need a thermostat/heater for temperature control?
What substrate recipe is best for monotubs?
The most popular substrate is CVG (Coco Coir, Vermiculite, Gypsum). A standard recipe is:
- 650g coco coir
- 2 quarts vermiculite
- 1 cup gypsum
- 4.5 liters boiling water
This mix retains moisture and provides structure. Some growers add hardwood fuel pellets for species like Psilocybe cubensis.
How do I properly prepare and pasteurize substrate?
- Mix ingredients in a food-safe bucket.
- Pour boiling water over the substrate and seal the bucket for 1-2 hours.
- Let it cool to room temperature before mixing with spawn.
Pasteurization kills contaminants while preserving beneficial microbes.
What’s the ideal spawn-to-substrate ratio?
Aim for 1:2 to 1:4 spawn-to-substrate ratio (e.g., 1 quart spawn for 2-4 quarts substrate). Higher spawn ratios colonize faster, reducing contamination risks.
Do I need a casing layer, and if so, how do I apply it?
A casing layer (pH-adjusted peat moss or vermiculite) is optional but helps retain humidity for species like Psilocybe cubensis. Apply a 0.5–1-inch layer after full colonization. Other species, such as Panaeolus cyanescens and Psilocybe subtropicalis do require a casing layer.
How do I set up a monotub?
- Use a 40–66 quart sterilite tub.
- Drill 6–8 holes (2-inch diameter) around the tub for airflow (2 rows near the top and bottom).
- Line the tub with a plastic bag to prevent side-pinning.
Ideal temperature and humidity?
- Colonization: 75–80°F (24–27°C), 90%+ humidity.
- Fruiting: 70–75°F (21–24°C), 85–95% humidity.
How much light do mushrooms need?
Indirect ambient light (12 hours/day) is sufficient. Mushrooms use light as a directional cue, not for photosynthesis.
Managing fresh air exchange (FAE)?
Adjust hole placement or fan the tub 2–3 times daily. Overly dry substrate? Reduce FAE. Fuzzy mycelium? Increase FAE.
Preventing contamination?
- Work in a clean environment (use a SAB or flow hood).
- Pasteurize substrate properly.
- Avoid opening the tub during colonization.
Signs of contamination
- Mold: Green/black spots (trichoderma), sour smells.
- Bacteria: Slimy substrate, foul odor.
Saving a contaminated monotub
Isolate the tub immediately. If contamination is localized, cut out the affected area and spray with hydrogen peroxide. If widespread, bury the substrate outdoors.
How long does colonization take before fruiting?
Colonization typically takes 10–20 days, depending on temperature, spawn ratio, and species. The substrate should appear fully covered in white mycelium before initiating fruiting.
When should I introduce fruiting conditions?
Switch to fruiting conditions once the substrate is 80–100% colonized. Introduce fresh air exchange (FAE), lower temperatures slightly (~70–75°F), and provide indirect light.
Why aren’t pins or mushrooms forming?
Common causes:
- Insufficient humidity: Mist walls lightly.
- Poor FAE: Fan more frequently.
- Low temperatures: Adjust to 70–75°F.
Scratching the surface (“forking”) or a light casing layer can help if the mycelium is overly dense.
Why aren’t pins or mushrooms forming?
Common causes:
- Insufficient humidity: Mist walls lightly.
- Poor FAE: Fan more frequently.
- Low temperatures: Adjust to 70–75°F.
Scratching the surface (“forking”) can help if the mycelium is overly dense.
How often should I mist and fan the monotub?
- Mist: 1–2 times daily (only if walls/substrate look dry).
- Fan: 2–3 times daily to promote FAE. Avoid over-misting, which can cause pooling.
When and how do I harvest mushrooms?
Harvest just before the veil under the cap breaks. Twist and pull gently at the base, or use a sterilized knife. Avoid disturbing nearby mycelium.
How do I rehydrate the substrate for additional flushes?
Soak the substrate in cold water for 1–2 hours, drain thoroughly, and return to fruiting conditions. Yields typically decrease with each flush.
What to do after the final flush?
Compost spent substrate outdoors or bury it in a garden. Clean the monotub with bleach or isopropyl alcohol before reuse.
What causes overlay/stroma?
Overlay (thick, matted mycelium) is caused by:
- Excess CO₂: Increase FAE.
- Low humidity: Mist gently.
Scrape the surface with a fork and reapply a casing layer to stimulate pinning.
Why are my mushrooms small or deformed?
- Poor genetics: Use quality spores or liquid culture.
- Inadequate FAE/humidity: Adjust airflow and misting.
- Nutrient depletion: Expect smaller fruits in later flushes.
Why is my substrate too dry or wet?
- Dry substrate: Soak longer during rehydration; mist more.
- Overly wet substrate: Increase FAE, reduce misting, and ensure proper drainage.
Can I reuse substrate or monotub materials?
- Substrate: No—discard after final flush.
- Monotub: Yes! Sterilize with 10% bleach solution before reuse.
How to maximize yields?
- Use high-quality spawn.
- Maintain stable humidity (85–95%) and FAE.
- Harvest on time to redirect energy to new pins.
Common beginner mistakes to avoid
- Over-misting: Leads to contamination.
- Skipping pasteurization: Invites mold.
- Neglecting FAE: Causes CO₂ buildup and poor growth.
How many flushes can I expect?
Most monotubs produce 2–4 flushes, depending on species and conditions. The first flush is usually the largest.
Are monotubs suitable for all species?
Best for most of the home grown Psilocybe species.
Storing harvested mushrooms
- Short-term: Store in a paper bag in the fridge for 5–7 days.
- Long-term: Dehydrate at 120°F until cracker-dry, then seal in airtight jars.
Do I need a thermostat or heater?
Only if your room is consistently outside the ideal range (70–80°F). Use a space heater with a thermostat for cold climates or a cooling fan for hot areas.
Final Thoughts
Monotub cultivation balances simplicity and productivity. By mastering humidity, FAE, and sterilization, you’ll enjoy bountiful harvests of homegrown mushrooms.
📝 Pro Tip: Document each grow to refine your process—every batch teaches something new!
🌱 Ready to start? Share your Growing Mushrooms in a Monotub journey in the comments below!
