Mycelium Troubleshooting: Differentiating Thriving Growth from Contamination

If you're new to mushroom cultivation, identifying healthy mycelium can feel like a challenge. While most people recognize the look of a fully-grown mushroom, understanding mycelium growth requires a bit more expertise. For first-time growers, it’s common to doubt whether what you're seeing is healthy mycelium or the onset of contamination.

At Spore Sorcery, we know that mycelium can look different depending on the species, the substrate, and even the growing conditions such as moisture levels and air exchange. Similarly, contamination comes in many forms and colors, making it tricky to identify at first. In this guide, we'll help you differentiate healthy mycelium from contamination so you can troubleshoot with confidence.

Not to mention, mycelium can look very diverse depending on the species you're growing or the substrate you're using. Environmental conditions such as moisture or fresh air exchange can also dramatically affect what mycelial growth looks like. Likewise, contamination can also come in many different forms and colors. Sometimes, it’s showy and colorful, but other times, it might not be so obvious.

What Does Healthy Mycelium Look Like?

While healthy mycelium can have distinct appearances, some attributes are consistent across species and environmental conditions.

 

	Healthy Mycelium	Contamination
Color	Mycelium is generally white. Some exceptions, like Pink Oyster and Cordyceps, have colored mycelium.	Gray, off-white, green, black, or other vibrant hues.
Appearance	Typically grows directly on the surface of the substrate. It may appear cottony after freshly inoculating or when mycelium runs out of nutrients.	Very cottony, fuzzy, or hairy. It may be more “aerial” or growing outward from the substrate surface.
Growth Pattern	Clear and visible branching pattern as it spreads. Some species grow mat-like (e.g., Turkey Tail).	Splotchy, irregular, and with no clear branching pattern.
Structure	Forms threads or cords that expand outwards. May form thick strands (rhizomorphs) on lower-nutrient substrates. Lion's Mane is an exception, with very thin mycelium.	It doesn’t usually spread with a thread-like growth but tends to be fuzzy.

Mycelium Appearance By Species

• Magic Mushrooms (Psilocybe cubensis): Forms notable thick thread-like and branching mycelium.

• Common Oyster (Pleurotus ostreatus): This includes many varieties, including white oysters, blue oysters, pearl oysters, and gray oysters. Oyster mushroom mycelium is white in color and notably branching, thread-like and vigorous. King Oyster (Pleurotus eryngii) looks very similar.
  
  
• Pink Oyster (Pleurotus djamor): Like common oysters, but pink in color and thinner. It rarely produces thick strands of mycelium.
  
  
• Yellow Oyster (Pleurotus citrinopileatus): Very similar to common oysters.
  
  
• Lion's Mane (Hericium erinaceus): Lion's Mane produces notably thin mycelium that can be difficult to spot. Occasionally, you may not even be able to see mycelial growth, although it's aggressively spreading on a substrate. As the mycelium matures, it thickens, becoming clearly visible and white. It is prevalent for Lion's Mane to fruit prematurely, forming small dense primordia in the substrate.
  
  
• Turkey Tail (Trametes versicolor): White, dense, and mat-like. The mycelium typically grows slowly and close together, often with no visible branching or strands.
  
  
• Shiitake (Lentinula edodes): White and oftentimes with notable branching and thick threads.
  
  
• Reishi (Ganoderma lucidum): White and slightly mat-like with some branching.
  
  
• Nameko (Pholiota nameko): White with light branching. Chestnut mushrooms (Pholiota adiposa) look very similar.
  
  
• Maitake (Grifola frondosa): White and fluffy, rarely forming thread-like mycelium.
  

What Is Contamination?

Contamination is the term used for a wide array of harmful microorganisms that impede the growth of mycelium and occasionally attack the fruiting bodies. It can originate from a poorly pasteurized/sterilized substrate or be introduced during inoculation, incubation, or fruiting.

 It is important to note that contamination tends to increase when the environmental conditions are ripe for its growth. For example, excessive moisture in a substrate, lack of fresh air exchange, or temperatures outside the ideal range for your mushroom will cause contamination rates to skyrocket. 

Identifying Contamination

Many beginners struggle to identify contamination simply because they do not know what normal mycelium looks like. Fortunately, identifying contamination is straightforward once you know what to look for. Contamination might not always be visible, but the side effects of its presence typically are.

• Green, Blue, Red, and Other Colors: The most apparent form of contamination is the colorful molds that can appear on your mycelium.
  • Green Mold (Trichoderma spp.) is a common and aggressive mold with a distinctive green color. It is the most common of all contaminants.
  • Black Mold (Aspergillus spp.) appears as black and powdery.
  • Blue/Green Mold (Penicillium spp.) is characterized by its blue or green color and fuzzy texture. While it doesn’t attack mycelium directly, it competes with it for resources.
  • Other contaminants can be green, red, yellow, black, or purple.
    
    
• White and Fuzzy: Certain forms of contamination look a bit like your mushroom mycelium and can be difficult to differentiate. These are often Cobweb Mold (Dactylium dendroides) or Cat Hair Fungus (Mucor sp.) which are wispy, light, and cottony compared to mushroom mycelium. These tend to be off-white or gray. They also spread vigorously, notably faster than mycelium.
  
  
• No Growth Zones: Often, contamination presents itself by the lack of growth within the substrate. These “zones of inhibition” are where other fungi or bacteria have been growing and producing compounds that inhibit the growth of mycelium. This is common in parts of the substrate with excess moisture or lack of air exchange. Occasionally, mycelium will colonize these zones.
  
  
• Slow Growth: When mycelium encounters contamination, its growth may slow significantly.
  
  
• Yeasty or Moldy Smells: Sometimes contamination can be identified by its smell. Yeasts have a particular smell reminiscent of fermenting dough or other yeasty foods. Molds typically have a dusty and moist odor reminiscent of a wet attic, basement, or inside a cupboard with a leaky faucet.
  
  
• Unhealthy Fruiting Bodies: Occasionally, contamination is only visible until the end of the life cycle during fruiting. Wet Bubble (Mycogone perniciosa) is a fungal infection that causes deformed, bulbous mushrooms with a wet, slimy appearance. Dry Bubble (Verticillium) is a counterpart that results in dry, brown spots on mushrooms and can stunt mycelium growth. Bacterial blotch causes brown spots on mushrooms and proliferates when there is excessive moisture.

Conclusion: Familiarize Yourself Mycelial Growth

Familiarizing yourself with healthy mycelial growth takes time and experience. Still, all you need is a couple of successful grows to have a good reference for what you should expect from healthy mycelium.

If you’ve been struggling with contamination, don’t lose enthusiasm! This is normal for beginner growers and part of the learning process. Eventually, you’ll develop the technique needed to get the large flushes of mushrooms you’re after

If you haven’t already checked it out, we recommend beginner growers to utilize pre-sterilized grains, substrate mixes, or all-in-one grow kits that can make the cultivation process a lot easier and significantly lower risk of contamination.