🛠️ Monotub Maintenance

1. Reading Surface Conditions

The surface of your substrate tells you everything. You want thousands of tiny droplets sitting on the mycelium, but NO pooling water.

The "morning dew" pattern — that sparkling scatter of fine water droplets across the mycelium surface — represents humidity equilibrium. It means the substrate is releasing moisture at approximately the same rate it is absorbing it from the ambient air, and the surface relative humidity at the substrate level is in the 90–95% range where pin initiation and development occur reliably. Dew forms preferentially on cooler surfaces, which is why you will often see heavier condensation on the walls and lid of the tub than directly on the substrate: the plastic is typically a degree or two cooler than the metabolically active mycelium. This wall condensation is normal and healthy; pooling water collecting at the bottom of the tub is not.

2. Daily Routine (The Schedule)

Consistency is key. Try to check your tub at least twice a day.

• Morning
  Check & Fan: Open the lid. Fan vigorously with the lid for 30 seconds to displace CO2. Check surface conditions. If dry, mist lightly above the tub (let it fall).
• Evening
  Repeat: Fan again to remove built-up CO2. Verify moisture.
• Note
  Modified Tubs: If you have a dialled-in modified tub (with holes and filters), you might not need to fan or mist at all. Just check visual cues once or twice daily.
• Troubleshoot
  Diagnostic Check: During each visit, actively scan for early warning signs beyond humidity. Look for pins that have stalled at the same size for more than 24 hours (pin abort, usually from CO2 or low humidity), any yellowing or browning of mycelium patches (bacterial activity or desiccation), an unusual sour or foul smell when the lid is lifted (bacterial contamination, act immediately), and any green or black discolouration on the tub walls or substrate surface (Trichoderma mold or bacterial blotch). Early detection of any of these signs allows intervention before a problem becomes a full contamination event.

3. Dealing with Side Pins

Mushrooms growing squished against the plastic wall are annoying to harvest and prone to rot.

Side pins form because of a micro-climate differential that develops between the bulk of the substrate and the narrow gap between the substrate edge and the tub wall. This gap has slightly different humidity, slightly different gas dynamics, and often slightly different temperature than the open top surface — and pin primordia form wherever conditions cross the threshold for initiation, including along this gap. The mycelium has no preference for the top surface versus the side; it simply pins where the environment is right. Once a side pin begins developing against the plastic, it cannot be moved without damaging both the pin and the underlying mycelium.

Prevention

Use a Liner: A black plastic liner (cut from a standard kitchen bin bag and shaped to fit the interior of the tub) is the single most effective prevention method. The liner sits between the substrate and the tub wall, eliminating the micro-climate gap. As the substrate shrinks slightly between flushes, the liner shrinks with it, maintaining contact and preventing the gap from reopening. No amount of post-hoc intervention is as effective as this simple mechanical barrier. Fit the liner before adding substrate — retrofitting it after colonisation is usually not feasible without disturbing the cake.

Management

If you already have them:

• Don't dig them out early: You'll damage the cake and create open wounds in the substrate that invite contamination.
• Wait for harvest: When harvesting the top, float the cake in water (fill the tub) to raise it up, then gently pick the side pins.

4. Rehydration (The Dunk)

After your first harvest, the cake will be dry and light. It needs water to produce again.

1. Clean the surface first: Before adding water, remove all harvested stumps, aborted pins, and any dead mycelium from the surface using a sterilised spoon or gloved fingers. These remnants will not fruit and serve only as contamination substrates once wet. A thorough surface clean now dramatically reduces between-flush contamination.
2. Fill the tub: Pour tap water gently down the inside wall until the substrate block is submerged or nearly so. Room-temperature water is ideal — very cold tap water can shock the mycelium, and very warm water risks heat stress.
3. Soak: Let it soak for 6–12 hours. A good baseline is roughly 1 hour per centimetre of substrate depth. Weigh down the block with a clean zip-lock bag filled with water if it floats. Do not exceed 12 hours — prolonged saturation begins to deprive the deeper mycelium of oxygen, effectively drowning the substrate. Beyond this point, anaerobic conditions favour bacterial growth over mycelial recovery.
4. Drain thoroughly: Drain ALL water and tilt the tub to allow any residual water to run off. Standing water pooling under or around the substrate block is the single most reliable way to trigger a bacterial contamination event between flushes.
5. Optional cold shock: After draining, place the substrate in a refrigerator at 4°C (39°F) for 12 hours. This temperature drop mimics an autumn cool-down and strongly stimulates pin initiation. This step is optional but worth doing for substrates that were slow to initiate their first flush.
6. Rest period: After draining (and cold shock if used), return the tub to normal fruiting conditions and allow 24–48 hours for the substrate to equilibrate before expecting pinning activity to restart. The mycelium needs time to re-establish moisture balance and recover metabolically before initiating new primordia. Do not disturb the tub during this rest period.

5. Between-Flush Contamination Check

The period between harvest and the appearance of the next flush is the window of highest contamination risk. The substrate surface has multiple harvest wounds, the mycelium is temporarily stressed from depletion, and the dunking process introduces ambient microorganisms. Knowing what to look for — and what to do about it — determines whether a contamination event ends your grow or remains a minor setback.

What to look for:

• Green patches (Trichoderma): The most common mold contaminant in mushroom cultivation. Appears first as white fluffy growth that rapidly transitions to a distinctive blue-green or olive-green colour as spores are produced. It spreads aggressively and produces compounds that inhibit mycelial growth.
• Black spots: May indicate cobweb mold (a less aggressive competitor that can sometimes be outcompeted by healthy mycelium with increased FAE) or bacterial blotch in darker forms. Bacterial black patches are typically wet and slimy; mold patches are dry and powdery.
• Pink or orange tints on the substrate surface: A strong indicator of bacterial blotch (wet rot). These colours are produced by specific bacterial species and are accompanied by a sour or foul odour. Act immediately.
• White fluffy growth at harvest sites: This is frequently healthy mycelium re-colonising the harvested area and should not cause alarm. Healthy regrowth mycelium is bright white, has a consistent cottony texture, and does not discolour. Contamination is distinguished by irregular texture, unusual colour, and smell.

Decision tree:

• Isolated green spot on tub wall, not touching substrate: Wipe with a dry paper towel, slightly reduce humidity and increase FAE. Monitor closely. This often originates from a spore that landed on the plastic and can be managed without losing the grow.
• Green on a discrete section of the substrate surface: Using a sterilised spoon, scoop out the contaminated section and a margin of surrounding material. Place the tub in a zip-lock bag to contain spores and transfer the removed material directly to an outside bin. Increase FAE and reduce humidity slightly. The remaining healthy mycelium may still produce another flush.
• Widespread green across multiple substrate areas, or any bacterial blotch with foul odour: The grow is no longer recoverable. Seal the entire tub in a plastic bag without opening it (to prevent spreading Trichoderma spores throughout your grow space), discard, and deep-clean the tub before any further use.

Proper harvest-site cleanup — removing all stumps and dead material promptly after each harvest — is the single most effective contamination prevention measure between flushes. Decomposing organic material on the substrate surface is the primary entry point for both bacterial and fungal contamination.

6. When to Retire a Monotub

Every substrate has a finite nutrient budget, and knowing when that budget is exhausted saves time and grow space that would be better directed toward a fresh tub.

Signs the substrate is exhausted:

• Flush yield has dropped more than 70% compared to Flush 1, even after thorough dunking and optimal conditions.
• Pins initiate but abort before reaching harvest size — the substrate can no longer provide enough nutrients to complete fruiting body development.
• The substrate block has shrunk dramatically, turned a tan or medium brown colour throughout, and feels significantly lighter than when fresh. This colour shift indicates the bulk of available cellulose and lignin has been metabolised.
• Colonisation of new surface growth after dunking is slow or fails to establish — the mycelium itself is depleted.

Disposal of spent substrate: Outdoor composting is the standard and most ecologically sound disposal method. Spent myceliated substrate is rich in fungal biomass, partially broken-down organic material, and chitin — all beneficial to soil structure and microbial communities. Simply incorporate it into an outdoor compost pile or spread it over garden beds. Do not compost substrate that showed signs of contamination; bag and bin it instead to avoid introducing Trichoderma or bacterial pathogens to your garden.

Tub sterilisation before reuse: A used tub requires thorough sterilisation before it can serve another grow. Soak the empty tub in a 10% bleach solution (roughly 100ml bleach per litre of water) for 30 minutes, ensuring all interior surfaces are in contact with the solution. Rinse thoroughly with hot water and allow to air dry fully before use. Alternatively, run the tub through a dishwasher cycle with standard dishwasher detergent. Inspect the interior for scratches or cracks in the plastic where residual contamination can harbour; if the tub is heavily scratched, discard and replace it.