Mushroom kit contamination identifier
Three questions about color, smell and species, with seller guidance on what to do next. It is a guide, not a diagnosis.
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Answer three questions to see what North Spore's guidance says.
How the questions map to the guidance
The three questions follow what North Spore says about telling mycelium from mold. The first looks at color, because white or off-white growth is usually mycelium, amber beads are harmless exudate, and black, green or orange patches may be transit damage or mold. The second asks about smell, because a healthy block smells earthy and a foul smell is a warning sign. The third adds the species, because oyster, lion's mane and shiitake blocks look different when they are healthy.
What it cannot do
It cannot see your kit, so it is not a diagnosis, and it never tells you to throw a kit out. It also leaves out any color the sources do not describe, and says so. If the result is a warning, the steps North Spore gives are the same every time: photograph it, keep the packaging and the batch sticker, and contact the seller before you open the kit. Our guide to mycelium vs mold has the longer explanation, and mushroom grow kit troubleshooting covers kits that look fine but are not growing.
Related pages
Common questions
Is this a diagnosis of my kit?
No. It reads back what North Spore and Field & Forest say about color and smell. Your seller can see photos of your kit, and a photo to them is always the better step.
What if my kit has white fuzz?
North Spore says white growth is usually mycelium, the mushroom itself. A healthy block has white or off-white mycelium through brown substrate and smells earthy.
What should I do if I see green mold on shiitake?
North Spore suggests spraying affected areas with 3% hydrogen peroxide, and Field & Forest suggests bleach in the soak water. Follow the sheet that came with your block, and contact the seller if it spreads.
Should I open the bag if I am not sure?
North Spore says to contact it with photos before you open the kit if you see green or black discoloration or smell something foul, and to keep the packaging and batch sticker.
Sources
- Is my kit growing mold?, North Spore help center. Checked November 11, 2026.
- Spray & Grow Kit FAQ, North Spore. Checked November 11, 2026.
- 3 pc. Organic Shiitake Fruiting Block Kit Bundle, North Spore. Checked November 11, 2026.
- Shiitake Ready-To-Fruit Blocks, instruction sheet, Field & Forest. Checked November 11, 2026.
How this page is checked
Cedrick Reese built this question flow from North Spore's help-center article on mold and its FAQ, with the shiitake green-mold advice from North Spore and Field & Forest. Every answer on the result screen is a statement one of those sellers makes, and where they differ the page says so. We have not diagnosed any kits ourselves, and the result always points to the seller for the final call.