How to Grow Mushrooms in Coffee Grounds

With the arrival of fall, temperatures are dropping, that cool familiar breeze is rolling in and for some, frost is starting to cover the ground. Whether this means that you’re in the homestretch of gardening outdoors or you’re just spending more time inside, food growing adventures do not have to end. 

From hydroponics to herb pots, there are lots of ways to grow things inside your home. But for those who want to get a little more experimental and expand your horizons past fruits and vegetables, growing your own oyster mushrooms can be a fairly low-budget and simple avenue to pursue. 

One cultivating method used by a number of urban farmers and “do-it-yourself” growers involves taking freshly used coffee grounds and a little bit of boiled straw as substrate (the soil) and mixing it with spawns of the mushrooms to grow into a new batch. With six million tonnes of spent coffee grounds being sent to landfills each year, it’s also an eco-friendly way to repurpose something that would otherwise be wasted. 

So if you want to dabble in basic mushroom cultivation, we’ve got the steps to take you through the process below. 

What You’ll Need: 

• Straw (pre-cut into four inch pieces) 
• Oyster mushroom spawns (you can buy online or from a local mushroom producer) *store in the fridge until use * 
• Freshly used coffee grounds 
• Isopropyl alcohol (at least 70 percent)
• Cooking pot 
• Clear plastic garbage bags or food storage bags
• Twist tie or elastic bands
• Kitchen Scale 
• Thermometer
• Strainer
• Salad spinner
• Gloves
• Spray bottle 
• Exacto knife 

Your mixture should roughly be 70 percent coffee grounds, 20 percent straw and 10 percent mushroom spawns. You can get precise measurements by weighing each item with your kitchen scale.

Use as much as you want, but here is an example of measurements to scale and how to make calculations: 

• 5 lbs of coffee grounds
• 0.5 lbs of mushroom spawns (weight of coffee x 0.10)
• 1 pound of straw (weight of coffee x 0.20)

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1. Wipe down all of your materials with rubbing alcohol. *Note: It is important to disinfect everything during this entire process to prevent the spread of unwanted bacteria.
   
   
2. Before you mix your spawns, coffee and straw together you’re going to want to pasteurize your straw. Do this by immersing your straw in boiled water at 170 degrees for an hour and fifteen minutes. You can determine the exact temperature of the water using your thermometer. 
3. Dump your straw into a strainer and then into a salad spinner to drain out excess water that is weighing down your straw. 
4. Take your freshly used coffee grounds and mix them with your straw in a container. Pull any clumps from the coffee apart with either sanitized utensils or your hands if you are using gloves. *Note: It’s important to use coffee that has been freshly brewed. This ensures that no mould has accumulated in the coffee.
   
   
5. Add your mushroom spawns and break them up if they’re in clumps. 
6. Dump this mixture into a clear plastic bag. You may want to use more than one bag depending on how much material you are working with. Reminder: This bag should be wiped down with alcohol. 
7. Seal them tightly using a twist tie or an elastic band. Make sure that there’s no air caught in the bag. 
8. Tip the bag upside down and using your X-acto knife poke two to three small holes, no more than half an inch in diameter, in the bottom (the part that you didn’t seal). Also poke two small ones on the front and two small ones on the back of the bag. 
9. Place your bags in a dark, ideally humid, environment (65-75 °F is ideal) and keep them there for about two to three weeks. You can check on it periodically for mycelium growth. Mycelium is the vegetative part of fungi, like a root or a stem that develops in a plant, before the final product is in full bloom. This stuff grows from the initial spores in your bag and you’ll know you have growth when you see a fluffy white substance start to make up the majority of your bag. Mycelium growth is a good sign and means you are on your way to producing baby mushrooms. 
10.  After the mycelium has taken over your coffee and straw mixture and you start to see little mushroom “pinheads” forming (at the two to three week mark), make your holes slightly larger. These can be two inches at most. 
11.  Move your bags into a lighter area with indirect sunlight, like a windowsill. At this point you can start to spray the bags with a light coating of water each day. Do this once in the morning and once in the evening. When the tops of the caps start to flatten, that’s when it’s time to harvest. This is usually within 10 days. Enjoy!