Is the white fuzz on my grow kit mycelium or mould?
Reading White Fuzz
Almost every new grower asks the same question in the first week: is this white fuzz the mushroom, or a mould? Usually, it's mycelium — here's how to tell.
Relevant to: Lion's Mane, Blue Oyster, Pink Oyster, Coral Tooth
Short answer: in the first two weeks, white, cottony growth on your substrate is almost always mycelium — the mushroom itself — rather than a problem. Genuine mould usually shows colour (green, black, pink, or orange) rather than staying white.
What healthy mycelium looks like
- Bright white, slightly fuzzy or cottony in texture
- Spreads evenly across the substrate surface
- Smells earthy or faintly mushroomy, not sour
What to actually be concerned about
- Colour: green, black, blue-grey, pink, or orange patches
- Smell: sour, rotten, or acrid rather than earthy
- Texture: slimy rather than dry and cottony
If you see colour or an off smell, it’s worth photographing the patch and checking it against the troubleshooting guide for a second opinion before deciding what to do next.
A common look-alike: “dog hair”
Sometimes Lion’s Mane and oyster mushrooms produce long, wispy aerial mycelium that looks a little different from the dense fuzz on the substrate itself — often called “dog hair” by growers. This is still mycelium, not mould, and typically settles down once fruiting conditions (fresh air, light, humidity) are introduced.