Mushroom Growing Troubleshooting Guide (Contamination, No Growth, Fruiting Problems)

Quick Reference

Expected Colonisation Times

Before troubleshooting, know what's normal:

If you see no growth after these timeframes, investigate further. Growing Cordyceps? Check our complete Cordyceps militaris cultivation guide for species-specific troubleshooting, temperature requirements, and harvest timing.

Contamination Issues

Contamination is the most common problem in mushroom cultivation, affecting oyster mushrooms, Lion's Mane, and Cordyceps growers alike. Early identification and response is crucial.

Green Mould (Trichoderma)

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Appearance: Bright green patches, often starting white then turning green within 24–48 hours

Causes:

• Poor sterile technique during inoculation
• Substrate not fully sterilised (requires 90 minutes at 15 PSI)
• Contaminated culture source
• Working in unclean environment

Solutions:

• Discard contaminated containers immediately (outside, sealed)
• Review your sterile technique
• Ensure pressure cooker reaches and maintains 15 PSI for full duration
• Clean and sanitise your workspace thoroughly

⚠️ Beginner Mistake: Opening contaminated jars indoors spreads millions of Trichoderma spores throughout your home. Always dispose of contaminated containers outside, sealed in a bag.

Using a still air box dramatically reduces contamination risk during inoculation.

Cobweb Mould

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Appearance: Wispy, grey, fast-spreading growth that looks like spider webs. Spreads visibly within hours.

Cobweb mould is particularly common with oyster mushroom grows due to the high humidity requirements (85–95%).

Causes:

• High humidity with poor air circulation
• Contaminated casing layer
• Spores present in growing environment

Solutions:

• Increase fresh air exchange
• Reduce humidity slightly (try 80–85%)
• Can sometimes be treated with hydrogen peroxide spray (3%) if caught within the first 24 hours

⚠️ Beginner Mistake: Misting directly onto the substrate instead of the walls. This creates wet spots where cobweb thrives.

Bacterial Contamination

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Appearance: Wet, slimy patches, often with sour or fermented smell

Causes:

• Excess moisture in substrate (over 65% hydration)
• Unsterilised water for misting
• Dirty equipment

Solutions:

• Ensure substrate is at proper moisture content (60–65% for most species)
• Use only sterilised or distilled water
• Clean all equipment between uses

Growth Problems

No Growth After Inoculation

Possible causes and solutions:

1. Dead culture

   • Check if culture was stored properly (refrigerated, not frozen)
   • Consider using fresh liquid culture syringes for reliable results
   • Contact supplier for replacement

2. Temperature too low

   • Oyster and Lion's Mane colonise fastest between 21–24°C
   • Below 18°C, colonisation slows dramatically
   • Below 15°C, most species stop growing entirely
   • Use a heating mat if needed

3. Temperature too high

   • Temperatures above 30°C can kill mycelium within hours
   • Cordyceps is particularly sensitive - keep below 26°C
   • Move to cooler location immediately

4. Insufficient moisture

   • Grain may have dried during sterilisation
   • Properly hydrated grain should feel moist but not wet
   • Next batch, check moisture content before loading

⚠️ Beginner Mistake: Placing grain jars near a window or heat source. Temperature fluctuations of more than 5°C stress mycelium and invite contamination.

Slow Colonisation

Blue oyster mushrooms colonise quickly and often show visible white growth within 3–5 days. Lion's Mane takes 5–7 days to show first signs. If you're not seeing growth within these timeframes, consider these factors:

Possible causes and solutions:

1. Sub-optimal temperature

   • Check and adjust incubation temperature to 21–24°C
   • Consider insulated incubation chamber
   • Avoid temperature swings of more than 3°C

2. Old or weak culture

   • Fresh cultures colonise 2–3x faster than old ones
   • Use cultures within their viability window (typically 2–3 months refrigerated)
   • Learn to make your own liquid culture for a constant supply

3. Too few inoculation points

   • Multiple injection points speed colonisation by 30–50%
   • Aim for 4+ points per jar, evenly distributed
   • More points = faster full colonisation

4. Grain too dry

   • Properly hydrated grain colonises faster
   • Ensure grains are plump and glistening before sterilisation
   • See our pressure cooker sterilisation guide for proper technique

Stalled Colonisation

When mycelium stops growing before full colonisation (typically at 50–80%):

1. Check for hidden contamination - Sometimes contam isn't visible until it sporulates
2. Verify temperature is consistent (21–24°C)
3. Ensure gas exchange - CO2 buildup above 5% can stall growth
4. Check substrate moisture - May have dried out through filter patches

King oyster mushrooms are particularly prone to stalling if conditions aren't optimal - they require more precise temperature control than other oysters.

Fruiting Problems

No Pins Forming

Possible causes:

1. Not fully colonised - Wait for 100% colonisation (white throughout)
2. No fruiting trigger - Introduce cold shock (drop to 10–15°C for 12–24 hours), light, or fresh air
3. Wrong conditions - Check temperature (15–21°C for fruiting) and humidity (85–95%)
4. Substrate too wet - Reduce misting frequency

Lion's Mane requires high humidity (90–95%) but excellent air flow to initiate pinning. Without adequate FAE, it produces malformed "coral-like" growth instead of proper lions mane teeth.

Solutions:

• Ensure substrate is fully colonised before fruiting
• Introduce 12h light cycle (indirect daylight or 6500K LED)
• Lower temperature 5–10°C for cold shock
• Increase fresh air exchange to 4–6 times daily
• Mist walls, not substrate directly

Aborted Pins (Aborts)

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Appearance: Small pins (under 1cm) that stop growing and turn dark/brown

Causes:

• Humidity fluctuations (drops below 80%)
• Temperature swings (more than 5°C variation)
• Contamination stress
• Genetic factors (some strains abort more than others)

Pink oyster mushrooms are particularly sensitive to humidity drops - even 30 minutes below 80% humidity can trigger mass aborts.

Solutions:

• Maintain stable humidity (85–95%)
• Keep temperature consistent within 2–3°C
• Remove aborts to prevent rot
• Some aborts are normal (5–10%) - focus on healthy pins

Fuzzy Feet

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Appearance: Fluffy white mycelium growth at base of stems, sometimes climbing 1–2cm up the stem

This is extremely common with oyster mushroom varieties including blue oyster, pink oyster, and phoenix oyster. The mushrooms are still perfectly edible.

Causes:

• Insufficient fresh air exchange
• CO2 buildup above 1000ppm at substrate level

Solutions:

• Increase FAE frequency (fan 4–6 times daily)
• Raise humidity while increasing air flow
• Position fan to gently circulate air without drying out pins

⚠️ Beginner Mistake: Sealing the growing chamber too tightly to maintain humidity. This causes CO2 buildup and fuzzy feet. You need air exchange even at the cost of some humidity.

Small or Deformed Fruits

Possible causes:

1. Low humidity (below 80%) - Causes dry, cracked caps and stunted growth
2. Poor genetics - Some cultures produce smaller fruits after multiple transfers
3. Insufficient nutrients - Depleted substrate on 2nd/3rd flush
4. Overcrowding - Too many pins competing for nutrients

King oyster mushrooms require more substrate nutrition than other oyster varieties - supplement with wheat bran (10–15%) for larger fruits.

Environmental Issues

Humidity Too Low

Signs: Cracked caps, aborts, pins drying out, stems with dry fibrous texture

For most gourmet species, humidity should stay between 85–95% during fruiting.

Solutions:

• Add additional misting (3–4 times daily)
• Seal growing chamber better
• Add water reservoir (perlite tray maintains 90%+ humidity)
• Use humidifier if needed

Humidity Too High

Signs: Pooling water, bacterial growth, overlay (thick mat of mycelium on surface)

Humidity consistently above 98% creates problems.

Solutions:

• Increase fresh air exchange
• Wipe excess water from surfaces
• Improve drainage
• Crack lid slightly for air exchange

Temperature Fluctuations

Signs: Aborts, stalled growth, increased contamination risk

Temperature swings of more than 5°C stress mycelium and invite contamination. Cordyceps is especially sensitive to temperature swings and prefers stable conditions (22–24°C ± 1°C).

Solutions:

• Use thermostat-controlled heating
• Insulate growing space
• Avoid placing near windows or external walls
• Monitor with min/max thermometer

When to Start Over

Sometimes the best solution is to start fresh. Consider discarding and restarting when:

• Contamination has spread beyond a single spot
• Growth has stalled for more than 2 weeks with no improvement
• Multiple problems occurring simultaneously
• Strange smells (sour, fermented, chemical) appearing
• You're spending more time troubleshooting than growing

Starting fresh with clean technique is often faster than trying to save a compromised grow.

Prevention is Best

Review our guides on sterile technique and still air box basics to prevent problems before they occur.

Keep detailed notes of each grow to identify patterns and improve your technique over time.

Related Guides

Build your knowledge with these complementary resources:

• Liquid Culture Guide - Create and maintain healthy cultures
• Sterile Technique - Master contamination prevention
• Still Air Box Basics - Essential equipment for clean inoculation
• Blue Oyster Cultivation Guide - Complete growing guide for beginners
• Phoenix Oyster Cultivation Guide - Hardy and forgiving species
• Cordyceps Cultivation Guide - Advanced cultivation techniques
• Pressure Cooker Sterilisation - Proper substrate preparation

Frequently Asked Questions

How do I know if my mushroom grow is contaminated?

Look for any colours that aren't white mycelium - green, black, pink, or orange patches indicate mould contamination. Wet, slimy areas with a sour smell suggest bacterial contamination. Healthy mycelium for oyster mushrooms, Lion's Mane, and most gourmet species should be bright white and have a pleasant, mushroomy smell.

Can you save a contaminated mushroom jar?

No. Once contamination is visible, it has already spread microscopic spores throughout the container. Discard contaminated jars immediately - sealed and outside - to prevent spreading spores to your other grows. It's not worth risking your entire growing area.

Why is my grain spawn not colonising?

The most common reasons are temperature issues (below 18°C or above 28°C), a dead or weak culture, or improper moisture content in the grain. Check that your incubation area is 21–24°C, verify your culture source is reliable, and ensure grains were properly hydrated before sterilisation.

What causes fuzzy feet on mushrooms?

Fuzzy feet are caused by low fresh air exchange (FAE), resulting in CO₂ buildup at the substrate level. This is especially common with oyster mushrooms. Increase ventilation and air circulation to resolve the issue - the mushrooms are still perfectly edible.

How long should colonisation take?

This varies by species. Blue oyster mushrooms colonise quickly, often showing visible growth within 3–5 days and full colonisation in 2–3 weeks. Lion's Mane is slower, typically taking 5–7 days for first signs and 3–4 weeks for full colonisation. Cordyceps can take 7–10 days for first signs and 4–6 weeks for full colonisation. If you see no growth after 7–10 days, there may be an issue with temperature or culture viability.