Grow problems
Is my mushroom block contaminated?
Updated
Healthy mycelium is white, sometimes with yellow or amber drops. Contamination usually shows as color: green, blue-green, black, pink, or orange patches, or wet, slimy spots that smell sour. If you see colored mold, bag the block, take it outside without opening it, and clean the area. Do not eat mushrooms from a moldy block.
Is it mold or mycelium?
- Mycelium: white, cottony or rope-like, smells earthy or like fresh mushrooms.
- Yellow or amber drops: normal liquid from the mycelium. Not mold.
- Fuzzy white growth on stems: usually mycelium reaching for air. Add fresh air.
- Colored patches or powder: mold.
- Wet, sour, or slimy patches: bacteria.
What does each kind of contamination look like?
| What you see | Likely cause | What to do |
|---|---|---|
| Green or blue-green powdery patches | Green mold, often Trichoderma | Bag and remove the block |
| Black or dark gray fuzz | Black mold | Bag and remove the block |
| Pink or orange powder | Fast molds such as Neurospora | Bag and remove at once, it spreads fast |
| Gray, wispy growth that spreads in a day | Cobweb mold | Spot treat early or remove |
| Wet, slimy, sour-smelling patches | Bacteria | Remove the block |
| Yellow or brown sticky spots on caps | Bacterial blotch from standing water | Harvest, then add fresh air |
What should you do with a contaminated block?
- Do not open it indoors. Mold spores spread when you disturb it.
- Put it in a trash bag, seal it, and take it outside.
- Wipe the tent, tub, or chamber with soap and water, then 70% isopropyl alcohol, and let it dry.
- Wash your hands and anything that touched the block.
A block with green mold will not recover, and mushrooms from it are not worth the risk. Compost it outside, away from other grows, or throw it out.
Can you save a block with cobweb mold?
Sometimes. Cobweb mold is gray and wispy and spreads very fast. Some growers spot treat small patches early with 3% hydrogen peroxide and more fresh air. If it comes back, remove the block.
Why does contamination happen?
Mold spores and bacteria are everywhere, in the air, on hands, and on every surface. A healthy, fully colonized block usually wins because the mycelium has already claimed the food. Contamination wins when it gets in early or when the block is weak:
- The bag was opened or damaged before the mycelium finished.
- The substrate was not sterilized or pasteurized well enough.
- The block sat too warm, which helps green mold and bacteria.
- The air was wet and stale for days.
- The block is old and has given its best flushes.
What if mold shows up after a flush?
A block that has fruited two or three times has less food left and weaker defenses, so mold often shows up late. Small spots of green on a spent block mean it is done. Harvest anything clean that is already growing, then bag the block and remove it. Many growers put spent blocks in an outdoor compost pile or under wood chips, where they sometimes give one last flush on their own.
How do you prevent contamination?
- Buy blocks and cultures from a supplier that sells clean, labeled products.
- Do not open bags before they are fully colonized.
- Clean your hands, tools, and chamber before each grow.
- Keep fresh air flowing. Stale, wet air favors bacteria and mold.
- Pick species that colonize fast. Oysters such as Pearl Oyster outrun most molds.
- Harvest on time and remove old mushrooms. Rotting fruit invites mold.
FAQ
Can you eat mushrooms from a contaminated block?
It is safest not to. Mold can spread into the mushrooms before you can see it. Grow a new block instead.
Is green mold on mushrooms dangerous?
Green mold mainly ruins the grow. Its spores can irritate lungs and allergies, so do not open or shake a moldy block indoors.
Why is there yellow liquid on my mushroom block?
Yellow or amber drops are normal. The mycelium makes them, especially when it is stressed or nearly done colonizing. They are not mold.
Does contamination spread to other blocks?
It can. Spores from an open moldy block drift to nearby blocks and surfaces. Remove it quickly and clean the area before the next grow.
What is the white fuzz on my mushroom stems?
Usually mycelium reaching for fresh air, not mold. It goes away when you add more air changes.