You can grow oyster mushrooms indoors with used coffee grounds in the comfort of your own home! True story. I’ll explain how in this article. The methods used are based off of Trad Cotter’s in Chapter 10 of Organic Mushroom Farming and Mycoremediation (2014)*. This is so fun and easy! Anyone can do it.
What You’ll Need
- A clean container with a lid, BPA free. I used a glass jar. You can also drill a plastic container with holes to allow for fruiting on the sides, but you will need to mist these openings.
- Enough coffee grounds to fill your container, with or without paper filters
- Grain- or sawdust- oyster mushroom spawn. I used a 5 lb. bag of sawdust spawn for this adventure. The majority of the spawn from my 5 lb. bag was used to make oyster mushroom straw beds. Then I saved a little to grow them with the methods explained here.
The Recipe to Grow Oyster Mushrooms with Spent Coffee Grounds
Save your spent coffee grounds every day and stick them in a sealed bag or container in the fridge until it’s pretty full (enough to fill a container for growing your mushrooms). Don’t drink coffee? No worries! Me neither. Just ask family or friends to save their coffee grounds, or ask a local coffee shop for their spent coffee grounds. They’re just going to be tossed out, but you’re going to put them to good use! I would say spent coffee grounds stay good in the fridge for two or three weeks. Of course you can freeze them for longer storage if you’d prefer.
With clean hands, grab some coffee grounds and squeeze any excess coffee out until well-drained. They should be moist with a few drops of coffee liquid coming out when squeezed. Now, put a layer of coffee grounds in the bottom of your container, roughly an inch thick. This does not need to be exact. You’ve got this!
They’re ya go! They’re in, right? And just for fun, I boiled some pistachio shells and a few medjool date seeds kickin’ around for a few minutes, drained them, and added some to the spent coffee grounds (super optional). Then, work the outside of your spawn bag to break the grain or sawdust spawn into small bits. Next, sprinkle a thin layer of spawn over the the coffee grounds. A little goes a long way.
Continue alternating layers, adding a layer of coffee grounds followed by another layer of spawn. Stop until you have about an inch of space left at the top of your container. Let the last layer be coffee grounds and coffee filters bags (if present) to protect the final layer of spawn added.
Take a clean and clear plastic baggy and cut or poke small holes in it. Then place it over your jar to serve as a humidity tent. Here is a jar just one day after inoculation. You can already start to see the white mycelium spreading in the layers of spawn.
Watch Your Oyster Mushrooms Grow Indoors
Here is my jar sixteen days after starting it. I inoculated my golden oyster straw beds on the same day I started the coffee ground jar, and they began fruiting only a few days apart. *Tip: If you are growing oyster mushrooms in outdoor straw beds, starting an oyster mushroom coffee jar on the same day as the straw beds can help. They will likely fruit around the same time, serving as a reminder. This way, you don’t miss out on harvesting your oyster mushrooms when they’re at peak ripeness!
Here we have some golden oyster mushrooms twenty-two days after inoculating the coffee grounds.
Finally, these beauties are at full maturity on day twenty-four. Note that each individual mushroom will be a different size in the bunch, but they are all as big as they’re going to get. So better to harvest them all now! A week or two later, the golden oyster fungus produced a second flush in the jar, just a single mushroom. This jar was pint-sized, so a much bigger container could produce more flushes and higher yields. Once your fungus has produced one or two flushes, you can try feeding it more nutrients, perhaps in your garden or a fresh straw bed. It might fruit again. However, if the substrate is spent in nutrients or contaminated with mold, you can use it as compost in your garden.
These golden oyster mushrooms were grown using sawdust spawn from North Spore, and is the same exact spawn I used to make my golden oyster mushroom straw beds.
*Full Reference: Cotter, T. (2014). Organic Mushroom Farming and Mycoremediation: Simple to Advanced and Experimental Techniques for Indoor and Outdoor Cultivation. (1st ed.). Chelsea Green Publishing.