I'm growing oyster mushrooms in a plastic bag on sterilized cardboard and coffee grinds. I was quite stringent with cleanliness at set up, and it's been OK for a couple of weeks, but now there are green patches on the surface of the substrate. I scraped them off with a spoon and chucked them, but I might have pushed a bit deeper into the substrate by accident. How bad is this stuff, and does salt really work to get rid of it ? Will the oyster mycelium fight the green, do they coexist, or will the green harm the oyster mycelium ? Thanks.

enter image description here enter image description here

  • Pictures, please?
    – Stephie
    Jan 2, 2018 at 17:07

1 Answer 1


If you're trying to grow mushrooms vs creating a cardboard culture, then you might try and salvage it by burning the contamination out by using a magnifying lens. However, you're introducing billions of presumably trichoderma spores into your environment if that fails.

Another possibility is to try and salvage some clean looking mycellium and start another culture going. Although ostreatus is supposed to be quite aggressive, I've seen green mold take it over.

  • Well, it's only part cardboard, mostly it's a big pile of coffee. I wonder if it's too wet as well, it is quite boggy. The oyster mycelium are growing though. It's grey winter where I am so I can't burn it but thanks for the idea I hope it's useful for someone else. The mold started as white patches but I left them because I wasn't sure if it was oyster mycelium or not. In retrospect I should have scraped them off but I will know the difference in future grows. I think it should be easy to tell the difference between the mold and the rather fluffy oyster mycelium , Jan 3, 2018 at 11:00
  • You can't really grow on 100% coffee grounds. You need to alternate the layers between cardboard and coffee grounds. I also see white patches on coffee grounds and I think it just changes shape when on coffee vs the strandy mycellium on cardboard. Jan 3, 2018 at 17:56
  • Hi thanks, I think there's a mixture. I posted a photo which shows the green but also there is plenty of white fuzz which doesn't really show in the pic. The green is spreading pretty fast all over the sides. I'm wondering if I can dig out the oyster mycelium and use that for spawn or if that's too risky. Jan 4, 2018 at 15:13
  • BTW my grow smells cheesy, is this bad ? Jan 4, 2018 at 20:04
  • You can always try and recover some oyster mycellium to attempt another start on cardboard. Dunno about cheesy smells but cheese is grown with molds. Jan 4, 2018 at 20:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.