How to Grow Mushrooms in a Monotub Fruiting Chamber: A Step-by-Step Guide

 

Materials You'll Need:

  1. Monotub (Plastic tote, around 18–30 gallons, with modified air holes)
  2. Spawn (Grain spawn, colonized with mushroom mycelium)
  3. Bulk substrate (Coco coir and vermiculite, or a pre-made substrate mix)
  4. Micropore tape (or polyfill) for covering air holes
  5. Black trash bag (to line the tub)
  6. Spray bottle for misting
  7. Gloves (for sterility)
  8. Rubbing alcohol (for sterilizing)
  9. A drill and 1.5–2 inch drill bit (to make air holes in the tub)
  10. Aluminum foil (to cover the tub during colonization)

 

Step 1: Prepare Your Monotub

  1. Get your plastic tub: Choose a clear tote around 18–30 gallons in size. You'll need to modify it by adding air holes.
  2. Drill air holes: Using a drill with a 1.5–2 inch drill bit, create 4–6 holes around the sides of the tub (typically 2 holes on each long side, about 4–6 inches up from the bottom). You can also add holes near the top for airflow.
  3. Cover the holes: For now, cover these holes with micropore tape or polyfill to allow for gas exchange but prevent contamination.

 

Step 2: Prepare the Bulk Substrate

  1. Hydrate your substrate: If using coco coir and vermiculite, mix them in a 70:30 ratio (or follow the ratio provided in pre-made substrate kits). You'll need about 650g of dry coir and 2-3 quarts of vermiculite.  
  2. Sterilize the substrate: Though not necessary, pasteurizing your substrate can reduce the risk of contamination. You can do this by heating it at 160-180°F for about an hour.
  • Hydration step: Pour boiling water over the mixture in a clean bucket and cover it. Let it sit for 1-2 hours, then check if it’s properly hydrated. The substrate should feel moist but not soggy (no excess water when squeezed).

 

Step 3: Spawn Your Tub

  1. Sterilize your workspace and tools: Clean your working area and wear gloves. Use rubbing alcohol to wipe down surfaces and your hands.
  2. Mix the spawn with substrate: Line the bottom of your monotub with a black trash bag (this prevents light from reaching the bottom and causing mushrooms to pin there).
  • Pour the hydrated substrate into the monotub, saving some to sprinkle on top.
  • Add the colonized grain spawn (about 3-4 quarts depending on tub size), breaking it apart gently.
  • Mix the spawn and the bulk substrate evenly, ensuring all the grain is thoroughly spread out.
  • Finally, use the remaining substrate to cover the top in a 1-inch layer.

 

Step 4: Let the Tub Colonize

  1. Cover the tub: Place the lid on your monotub and cover the air holes with micropore tape to prevent contamination while allowing gas exchange.
  2. Let it colonize: Store the tub in a dark place at room temperature (65–75°F). It will take about 10–14 days for the substrate to fully colonize (turn white with mycelium). During this phase, avoid disturbing or opening the tub.
  3. Wait for full colonization: Check after a week. When the entire surface is covered in white mycelium, it’s ready for the next phase.

 

Step 5: Induce Fruiting Conditions

  1. Introduce light: After colonization, introduce indirect light (ideally 12 hours of light and 12 hours of dark). Natural daylight or low-intensity grow lights work well.
  2. Adjust humidity: Mushrooms need high humidity to fruit. Remove the micropore tape and replace it with loosely stuffed polyfill or leave the micropore tape if it allows sufficient gas exchange. Mist the inside walls of the tub lightly once a day to maintain moisture.
  3. Fan the tub: To encourage fresh air exchange, fan the tub a few times daily using the tub's lid or a piece of cardboard. This will help trigger pinning (the first tiny mushrooms).

 

Step 6: Maintain Fruiting Conditions

  1. Monitor your tub: Keep the environment humid by misting as needed, but avoid spraying directly on the mycelium or mushrooms. Maintain temperatures between 65–75°F.
  2. Wait for pinning: Tiny mushroom “pins” will start forming, usually within 7–10 days after switching to fruiting conditions. This is the exciting part!

 

Step 7: Harvest the Mushrooms

  1. Harvest at the right time: Your mushrooms are ready to harvest when the caps begin to open, exposing the gills underneath but before the caps fully flatten out.
  2. Twist and pull: Gently twist and pull the mushrooms at the base to harvest them. Try not to damage the substrate while harvesting.

 

Step 8: Second Flush and Beyond

  1. Misting and resting: After the first flush (harvest), continue misting and fanning the tub to maintain the humidity. Let the substrate "rest" for a few days.
  2. Second flush: Mushrooms often produce multiple "flushes" (harvest waves). Within another 1–2 weeks, new pins will form for another round of mushrooms.
  3. Keep harvesting: You can usually get 2–3 flushes from a well-maintained monotub.

 

Step 9: Clean Up and Reuse

  1. Disposal: Once the tub has stopped producing, you can dispose of the spent substrate by composting it.
  2. Cleaning your tub: Wash and sterilize your tub thoroughly if you plan to reuse it for another batch.

 

Tips for Success

  • Maintain cleanliness: Contamination is the biggest threat. Always sterilize your hands, tools, and workspace when working with the spawn or substrate.
  • Monitor humidity: Too little moisture will stop mushrooms from growing; too much can lead to contamination.
  • Patience is key: The entire process can take several weeks, but the reward of fresh mushrooms is well worth it.