Have you been wanting to grow mushrooms but didn’t know where to start? In this post, I’ll show you a simple way to experience the joy of mushroom cultivation using a free ingredient found in almost every American household — spent coffee grounds! That’s right. Instead of tossing those grounds in the garbage, you could be growing mushrooms using common household items. The only thing you will need to purchase is the mushroom spawn to inoculate the grounds.
Tools, Supplies, and Equipment
- Clean jar with lid (I use a quart mason jar)
- Spent coffee grounds (with or without paper filter)
- Paper towel, clean cloth, or other breathable material
- Isopropyl alcohol 70%
- Spray bottle with water
- Oyster mushroom spawn
Instructions
- Sanitize the jar by wiping with isopropyl alcohol. Allow the alcohol to evaporate.
- Sprinkle a small amount (1/2 – 1 tsp) of spawn into the bottom of the jar.
- Add a layer of coffee grounds (with or without the paper filter) and press down to minimize air pockets without creating a compacted brick.
- Sprinkle another small amount of spawn.
- Cover with a paper towel, clean cloth, or other material that will keep out gnats while allowing the mushrooms to breath.
- Repeat this process until the jar is filled to the base of the rim. You can build the layers over time, each day adding a new layer of grounds and spawn.
- Now for the hard part…waiting. But be patient and enjoy watching the process of the white mycelium spreading throughout the coffee. At this stage, the mushroom is digesting the coffee, extracting the nutrients it will need to form that delicious fruiting body.
- Once the mycelium has spread throughout the entire jar and a thick marshmallow like substance has formed on the top, the mushroom will begin to work on fruiting. As soon as you see pins begin to form (spikey-cauliflower-like formations at the top of the jar) begin misting the mushrooms with water. Be careful to not spray too much. There should be no pooling of water. The goal is to keep the mushrooms hydrated. Keeping the paper towel or cloth lid on can help to retain moisture.
- Once the mushrooms have grown to the top of the jar, remove the lid and continue misting throughout the day. Allow the mushrooms to have indirect lighting, which will stimulate the pigments creating the vibrant colors oyster mushrooms are known for.
- The mushrooms should double in size each day and are ready to harvest just before the edges of the caps begin to flatten out. Timing the harvest can be tricky and takes practice. Harvesting too soon reduces the yield while harvesting too late reduces the quality. Be patient with yourself as you learn to find the sweet spot.
That’s it! Contratulations. You have grown your very own mushrooms at home using a free and otherwise wasted resource. Don’t waste waste, we like to say. Enjoy your delicious harvest!
FAQ
- How much spawn should I use?
- There is no rule to the amount of spawn to use. More spawn will colonize faster and reduce risk of contamination; less spawn will be slower and increase risk of contamination. But less spawn is cheaper. Experiment to find your ideal balance. You might start with a teaspoon between layers and see how that goes.
- How fresh should the coffee grounds be?
- Coffee grounds should be no older than 24 hours. The longer the grounds sit without being inoculated the greater the risk of contamination. However, make sure the grounds have cooled and are not dripping wet before adding to the jar. You should not see liquid pooling at the base of the jar.
- How large of a container can I use?
- In amounts greater than 2 pounds, coffee grounds have a tendency to compact, creating an anaerobic environment favoring other contaminating organisms. Quart jars are a convenient and reliable size, but feel free to experiment with other shapes and sizes. Compare yields from different containers.
- How many harvests (a.k.a. flushes) can I expect from my coffee jar?
- Mushrooms can flush as many as 4 times, but each flush will be smaller than the previous one. I typically keep my batches around for 2 flushes before tossing out the substrate into our garden.
- Where can I find spawn?
- Reach out to me at contact@bucketeerfarm.com for my updated list of recommended spawn suppliers. If you live in the Mission Valley, Montana, I may even be able to supply you some of my own. Hit me up!