Growing mushrooms using the monotub method is a popular choice for both beginners and experienced cultivators. It offers a controlled environment that maximizes yield and minimizes contamination. In this comprehensive guide, we’ll explore how to grow mushrooms using the monotub method from start to finish, detailing all supplies needed, the step-by-step process, and how to troubleshoot common issues for a successful harvest.
What Is the Monotub Method?
The monotub method is a bulk growing technique that uses a plastic container (tub) as the growing chamber. It’s an efficient, cost-effective way to grow mushrooms indoors using simple materials and basic tools.
Supplies You’ll Need
Here’s a list of what you’ll need to start your mushroom cultivation journey using this method:
- Plastic storage tote with a lid (usually 18 gallons or larger)
- Drill with a 1/4-inch bit (for making ventilation holes)
- Polyfill, micropore tape, or filter patches (to cover ventilation holes)
- Coco coir or pasteurized horse manure (for the substrate)
- Vermiculite and gypsum (optional but beneficial for nutrient balance)
- Grain spawn of your chosen mushroom species
- Alcohol wipes or a spray bottle with isopropyl alcohol (for sanitizing surfaces and tools)
- Spray bottle with clean water (for misting and humidity control)
- Filtered or tap water (for hydrating substrate)
- Black trash bag (optional—used to line the tub for easier harvesting and cleanup)
👉 You can also buy an all-in-one monotub kit to simplify the process if you’re just getting started!
Step-by-Step: How to Grow Mushrooms Using the Monotub Method
Step 1: Prepare Your Monotub
- Drill ventilation holes into the plastic tote.
- On the long sides of the tub, drill two rows of holes: one about 2 inches above the intended substrate level, and another near the top edge.
- Stuff each hole with polyfill, or cover them with micropore tape or filter patches. These allow for gas exchange while minimizing the risk of contamination.
Here’s our favorite monotub to use from our friends at Midwest Grow Kits!
Step 2: Create Your Substrate
- Mix your substrate in a clean container. A popular bulk recipe is:
- 650g coco coir
- 2 quarts vermiculite
- 1/4 cup gypsum (optional)
- Add boiling water (approximately 4 quarts), stir well, and cover to allow it to pasteurize (target 160°F for 60–90 minutes).
- Once cooled to room temperature, it should feel like a wrung-out sponge—not dripping wet.
Or you can buy premade substrate here from our friends at Midwest Grow Kits!
If using horse manure, ensure it’s properly aged and pasteurized to kill harmful microbes.
Step 3: Inoculation (Mixing in the Spawn)
- After substrate is fully cooled, mix it with your colonized grain spawn.
- Use a ratio of about 1 part spawn to 4–5 parts substrate.
- Line the tub with a trash bag if desired, then spread the mixture evenly across the bottom of the tub, smoothing the surface with gloved hands or a sterile spoon.
Step 4: Colonization Phase
- Close the lid and store the monotub in a dark or dimly lit area at room temperature (70–75°F is ideal).
- Over 10–14 days, white mycelium will begin to colonize the entire substrate surface.
- Do not open the tub unnecessarily—this increases the risk of contamination.
- Once the substrate is completely white and fluffy, you’re ready to move to the next phase.
Step 5: Fruiting Conditions
- Introduce fresh air exchange (FAE) by loosening polyfill in the holes and exposing the tub to indirect light for 12 hours/day (a simple LED or window light works well).
- Mist the inner walls of the tub lightly to maintain 85–95% humidity.
- Fan the tub gently 1–2 times per day if necessary.
- Maintain temperatures between 65–75°F during fruiting.
Step 6: Harvesting
- Within 5–7 days of fruiting, mushroom “pins” will form and grow quickly.
- Harvest when the veil beneath the cap begins to tear but before it fully breaks.
- Gently twist and pull the mushrooms from the substrate, or cut them at the base with a sterile knife.
- Avoid letting mushrooms over-mature, as they’ll release spores which can affect future flushes.
Troubleshooting & Common Issues
Even with careful planning, challenges can arise during mushroom cultivation. Here’s how to recognize, fix, and prevent the most common problems in monotub growing:
1. Contamination (Mold or Bacteria)
Symptoms: Green, black, gray, or pink spots; sour or foul smell.
Cause: Unsanitary tools, poor pasteurization, contaminated spawn.
Fix: If contamination is extensive, discard the tub safely. For minor contamination, isolate or remove the affected area—though success varies.
Prevention Tips:
- Sterilize tools and surfaces.
- Use clean spawn from a reliable source.
- Avoid opening the tub during colonization.
2. Slow or Stalled Colonization
Symptoms: Mycelium is spreading slowly or not at all after several days.
Cause: Wet or dry substrate, low temperatures, poor-quality spawn.
Fix: Adjust substrate moisture (should feel like a damp sponge), and ensure a stable temp of 70–75°F. If no growth at all, your spawn may be dead or contaminated.
3. Fuzzy Stems or Tall, Thin Mushrooms
Symptoms: Mushrooms are “leggy” with fuzzy feet.
Cause: Lack of fresh air exchange (FAE).
Fix: Loosen polyfill more or fan the tub gently a couple of times per day. Be careful not to dry out the substrate—balance is key.
4. Fully Colonized but No Pinning
Symptoms: The substrate is fully white, but no mushrooms are forming.
Cause: Fruiting conditions not properly triggered—low light, low humidity, or no airflow.
Fix: Introduce indirect light, mist the tub walls, and increase airflow. Pins should appear within several days.
5. Overlay (Thick Mat of Mycelium)
Symptoms: A dense white crust forms on the surface, preventing pins.
Cause: Delayed fruiting or CO₂ buildup.
Fix: Lightly scratch the surface with a sterile fork to break the crust, then improve airflow and introduce light.
6. Standing Water or Soggy Substrate
Symptoms: Water pools on the substrate surface.
Fix: Use a paper towel to wick it away and avoid misting the substrate directly. Mist tub walls instead to retain high humidity without waterlogging.
Tips for Success
- Label your tub with the inoculation date to track progress.
- Keep a grow journal to log substrate recipes, flush yields, temperature, and humidity.
- Don’t over-fan—this dries out the tub and stresses the mycelium.
- Work cleanly—even minor contamination can ruin an entire batch.
- Be patient! Mushroom cultivation is a natural process. Don’t rush it.
Conclusion
Growing mushrooms using the monotub method is an efficient and rewarding way to dive into the world of home mycology. With a simple setup, a bit of patience, and attention to cleanliness and environmental conditions, you can produce multiple flushes of delicious mushrooms from one tub.
Whether you’re doing this as a fun hobby, a way to grow functional fungi like lion’s mane or oyster mushrooms, or even as a small business experiment—this method gives you consistent results at low cost.