What is mycelium?
Mycelium is the main body of a fungus, and the mushroom is its fruit. In a grow kit it shows up as a white or off-white network through the brown block, with an earthy smell.
The part you do not see
Mycelium is the main body of a fungus. North Spore puts it simply: the mushroom is to the apple what the mycelium is to the tree. In a kit, the mycelium is the white or off-white network through the brown block, and the mushroom is what it grows when conditions are right. See the mushroom life cycle for where mycelium sits among the four stages, and why one spore is rarely enough.
What it looks like in a kit
North Spore says a healthy block has white or off-white mycelium weaving through brown substrate, with an earthy smell. It varies by species. Oyster can form a thick, leathery mat, golden oyster is thick and white, and lion's mane is faint and often looks uncolonized when it is fine.
Amber beads on the surface are harmless mycelial exudate, per North Spore.
Mycelium or mold?
Most white fuzz on a fresh block is mycelium. North Spore says black, green or orange patches may be transit damage or mold. Our guide on mycelium vs mold covers what to do, and the contamination identifier asks a few questions to help you work out the next step. For the full growing method, see how to grow mushrooms at home.
Common questions
What is mycelium?
Mycelium is the main body of a fungus. North Spore compares the mushroom to an apple and the mycelium to the tree.
What does healthy mycelium look like?
North Spore says a healthy block has white or off-white mycelium weaving through brown substrate, with an earthy smell.
Why can't I see any mycelium on my lion's mane block?
North Spore says lion's mane mycelium is faint, and a fine block often looks uncolonized.
Sources
- Is my kit growing mold?, North Spore help center. Checked November 11, 2026.
- Spray & Grow Kit FAQ, North Spore. Checked November 11, 2026.
- Using a Spray & Grow Kit, North Spore. Checked November 11, 2026.
How this page is checked
Cedrick Reese wrote this explainer from North Spore's help-center and kit pages. We kept it to what the kit looks like, because that is what a grower needs to recognize. We have not photographed or tested kits for this page.