Coffee Grounds and Mould
Mould on coffee grounds is one of the most common things I get asked about, and up until a recent weekend experiment I had a shed floor covered in used coffee grounds to find out exactly what happens. Another lot was sitting in a cardboard box. The idea was simply to see what happens in a cold and dry environment.
Yes these are the sorts of things that I find interesting. Let’s not dwell on it too long 🙂
Here we have some 4 month old grounds, covered over with fungi. I have seen this happen without fail to damp grounds regardless of whether they are in a plastic bag, a bucket, or piled in a heap on the garden or around plants. As you can see from the photos, it has spread through the entire pile. So to answer one of the questions I’m asked about all the time: will mold grow on used coffee grounds? The answer is yes (if they are kept damp).
Coffee Cake anyone?
Inside the cake, more coffee!
Even older: the box of 5 month old coffee grounds.
It seems that much of the fungi (which we also refer to as mould) drops off once the grounds are handled. Not having done an analysis of the type of fungus, I turned to the Internet, just like I do when I need to have a medical condition diagnosed.
Is there a Problem with Mould on Coffee Grounds?
The general consensus among the gardening community is that no harm will come to you when handling the type of fungi that make use of coffee grounds, and that it is just a natural step in the process of decomposition. There are many discussions online about fungus on coffee grounds confirming this view, and the general advice is consistent: it is a normal part of the breakdown cycle.
What I find works is by using the grounds before they visibly mould, avoiding keeping them in a pile when damp, or letting them dry out and then using them at a more appropriate time. It is not always easy getting hold of freshly made used coffee grounds, and I have had my fair share of collecting bags of mouldy coffee grounds. I’m not overly fussed what they look like, because they will end up the same, breaking down into the garden one way or another. If you want to avoid the issue entirely, read up on how to dry and store used coffee grounds properly.
If mouldy grounds are an issue for you, see if you can strike a deal to collect coffee grounds with a local coffee shop when they are fresh (same day or day after). Once you have a good supply of fresh grounds, the next step is putting them to work, and the best introduction to that is seeing how coffee grounds compost and soil building actually works in practice.
Like with anything else in the garden, take some simple precautions with gloves and a mask if things are dry and dusty. And wash your hands afterwards. There are billions of little creatures swimming around in those coffee grounds, like any other organic material.
If you have had an experience with coffee ground fungi growth, let us know in the comments below.
2011 Summer Update: Some more photos of mould on coffee grounds
This series of photos are from coffee pucks taken out of the worm farm, sitting in there for several weeks. See the variety of green to blueish to white mold growing on them?
It is as it should be.
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