Today I am super excited to share with you my latest adventures: how to grow mushrooms in used coffee grounds and cardboard! It’s a very simple technique of growing mushrooms that requires no sterilization or special tools. And it can be done at home indoors or outdoors in any season.
I learned this method of growing mushrooms from an expert ( see more in resources at the end ). I love the simplicity of it, and how it allows everyone to grow delicious mushrooms at home using easily accessible and mostly free materials.
Below is a video of how fast these Oyster mushrooms grew in just 4 days! Ready to come down the rabbit hole with me?
*Some resources in article are affiliate links. Full disclosure here.
Materials and tools to grow mushrooms at home:
- coffee grounds and cardboard: a match made in mushroom heaven. Coffee grounds are rich in nutrients, but can contaminate easily. Corrugated cardboard is not as rich and delicious to competing molds and bacteria, and the corrugation allows room for air and for the mycelium (mushroom roots) to run.
- mushroom spawn: think of them as seedlings for you to grow mushrooms. This beautiful box of Elm Oyster spawn ( Not all kits are spawn! See tips at the end!) came from 100th Monkey Mushroom , a wonderful family run business with many great products and tutorials. Eventually you can learn to grow your own mushroom spawn from mushroom stem base! But you do need great quality spawn to get started! (more on that at the end)
- 13 gallon clear medium size trash bags like these will come in handy throughout the process
- 70% to 99% rubbing alcohol to keep everything clean and reduce contamination
Step 1: prepare cardboard and container to grow mushrooms
When you have all the materials you need to grow mushrooms, ask for a bag of hot-off-the-press coffee grounds from the fabulous people at Starbucks, and soak some cardboard in water 1-2 days prior. The coffee grounds should be used on the same day, and the long soaking of the cardboard helps to hydrate the material for growing mushrooms.
Take a one-gallon plastic container, cut 3 sides of the lid. Poke and cut 4 to 6 small 1/4″ size holes to allow air exchange and drainage on the bottom. Wipe the inside and outside of the container with 70% to 99% rubbing alcohol.
When you try to grow mushrooms at home, the biggest challenge is contamination. So keep the working area as clean as possible, and work fast!
Another fun growing project you may love – How to create a strawberry tower planter with built-in reservoir!
Step 2: layering mushroom spawn, coffee grounds, and cardboard
Break up 20% to 25% of the oyster mushroom spawn for each 1 gallon container.
Keep some paper towel dipped in alcohol handy, and wipe your work surface, hands, and anything that would come in contact with the spawn.
First put down 2-3 layers of cardboard. I put the Starbucks mermaid bag in there for fun, but it’s not required!
Sprinkle some spawn, then cover with a thin layer of coffee grounds. The coffee grounds can be warm or cool, but should not be too hot or freezing cold to the touch.
When in doubt, always use more spawn, because it will give competing fungus and bacteria less chance to establish.
Repeat the layers till the container is filled. Top with a layer of cardboard, and close the lid. Small air gaps are fine.
Loosely drape a plastic bag over the container to allow for air exchange, but keep in moisture. The saucer on the bottom is to catch excess liquid, if any, and to pour them out so the growing medium won’t get soggy on the bottom.
Put the container in a dark place for 2 weeks. Check every few days to make sure it’s not drying out. (OK, I checked many times a day, well, too excited! ) Spray water inside the bag or lid of the container if needed.
Within just 4 days, the mycelium (mushroom roots) started to grow happily! See photo above. Isn’t it exciting to grow mushrooms?!?
Then the magical day came in about 20 days, when the first baby mushrooms ( primordia ) were spotted!!!
Dr. Seuss little forest!! Can you see them?
And a cluster popped out on the side too!
Just like on a fruit tree not all little fruits will ripen, the mushroom will decide to abandon some clusters and concentrate energy on other clusters.
Eventually, those on the top took over in this batch.
As soon as you see very dense white areas with little budding mushrooms, usually in about 2 to 4 weeks from the start, it’s time to move the container into a growing environment.
The keys are fresh air, bright light (enough to read in is good, which makes it possible to grow them indoors easily!) but no direct sun, and humidity in the air. Just like how it is after a rain in the forest, where we would see mushrooms coming up.
A clear large plastic trash bag with 10-20 small holes all around, propped over the container can be a simple and effective humidity tent for the mushrooms to mature.
If you are crazy in love with growing mushrooms, like I am, you can make a mushroom terrarium which works great indoors and out: drill 1/4″ holes on all sides and lid of alarge clear plastic storage bin, cover with the lid or drape a sheet of clear plastic if the bin is standing on the side like in the case.
Either way, mist the inside of the humidity tent with water 2 times a day in a dry environment, so there are water droplets visible most of the time. Placing some trays of moist Horticultural Perlite can reduce the need for daily misting since it will add moisture in the air.
Mushrooms can also be fruited under the shade of a tree, or in a greenhouse.
Did you see in the video how fast these mushrooms grow? That was over a 4 day period! In 3-5 days mushrooms can grow from 1/2″ tall to over 6″ tall! And yes they were delicious!
After a harvest, put the container in the dark room again to rest for 1-2 weeks, then move it to the fruiting environment for another flush of mushrooms. This process can be repeated 3 times. Some say 5 times! By the time I am publishing this, a second flush already started. Wow!
The spent growing medium can also be broken up and used outdoors in a garden for a chance of more mushrooms! Elm Oyster and cabbage family plants have a beneficial relationship. I will update you on this in future! ( Elm Oyster mushroom is actually a different species from Oyster mushroom, although tastes and looks similar. Both works great with this coffee grounds method. )
But our mushroom adventure does not end here!
Save the mushroom stem base with some white mycelium still attached, add them to some pre-soaked cardboard in a bag or container. Keep layering as you harvest more mushrooms. With a little patience, practice and good luck, you can grow your own mushroom spawn in a low-tech way.
In his inspirational book Mycelium Running – How Mushrooms Can Help Save the World, Paul Stamets gives lots of details on growing mushroom spawn from mushrooms in simple ways.
I am just starting to experimenting with this, looking good so far! I will give an update in a few months and add a link here.
Helpful Tips and resources on how to grow mushrooms at home:
- A big thank-you to James Wieser whose video inspired me to try this method!
- My favorite book on how to grow mushrooms for the home / hobby grower is Mycelium Running – How Mushrooms Can Help Save the World by Paul Stamets. His passion and knowledge is contagious! He shares lots of fun and low tech ways to growing many kinds of gourmet mushrooms which I just can’t wait to try!
- ready to grow mushroom “kits” are actually spawn with growing medium already gone through the work we did here, and ready to fruit. By starting with spawn (although it might be called “kits”), we get lots more mushrooms and more fun in the learning process!
- if you see contamination such as black or green mold, remove the moldy spots, and spray the area with hydrogen peroxide, which comes as 3%, diluted with 10 times water, which will be 0.3%.
Want more growing ideas?
Happy growing! =)