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Growing Mushrooms in Coffee Grounds: Complete Guide

oyster mushrooms in a bottle

Mushroom growing is increasing in popularity, especially with the major boom of home gardening and homesteading. With hundreds of recipes and sauces that contain them, growing your own oyster or shitake mushrooms is a great alternative to buying them from the grocery store. Not only do they grow within days, but they are also not difficult to grow, even if you have a brown thumb. With some coffee grounds from your morning coffee and a lot of moisture, you’ll have oyster mushrooms growing in no time. Here’s a quick guide on growing mushrooms in used coffee grounds:

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What are Mushrooms and How Do They Grow?

Mushrooms are a major source of nutrients, so it’s no surprise that many people enjoy eating and growing them. They’re packed with protein and have an umami flavor, a Japanese term to describe their unique earthy base flavor. Mushrooms are fungi, so they’re not exactly plants or animals. They grow similar to plants and “flower”, creating the classic stem and umbrella that everyone recognizes. But before flowering, the spores will turn into white clusters where the mushrooms will form.

Mushrooms produce spores to reproduce and root themselves in the ground with mycelium, which is stringy roots that remain underground. Mushrooms thrive in warmth, moisture, and swamp-like conditions, so growing them requires that type of environment. Though they’re not difficult to grow and will easily form on their own, especially with houseplants that prefer damp soil, it does take a little work to get them to grow when you want them.

oyster mushrooms on wooden background
Image Credit: kellyclampitt, Pixabay

Why Should I Use Coffee Grounds to Grow Mushrooms?

Coffee is great gardening and composting ingredient, a carbon-producing product that can help balance out soil and compost piles. But coffee is also a great substrate for mushrooms for one reason: it’s already pasteurized. When growing mushrooms, pasteurized soil is essential to prevent competing bacteria, fungi, and insects from growing inside.

Because used coffee grounds are already pasteurized, there are fewer steps to successfully growing mushrooms. The important thing to remember is to use same-day coffee grounds, which means you’ll have to use what’s in your coffee maker from today. If you use older coffee grounds, it’ll be too dry and may have mold spores forming without you knowing. The used coffee grounds also can’t be piping hot, so you’ll have to cool them down a bit before using them.

Coffee Grounds on Coffee Filter
Image Credit: Tyler Nix, Unsplash

Tips on How to Grow Mushrooms in Coffee Grounds

There are quite a few methods of growing mushrooms in coffee grounds, but the idea is consistent: same-day used coffee grounds, a substance or item that makes the coffee grounds breathable, and a lot of moisture. You will need a lot of coffee grounds, so try going to your local coffee shop and asking for their coffee grounds. Since they usually throw spent grounds out, they will probably give them to you without hesitation.

If you use sawdust to help the coffee grounds breathe, it must be pasteurized to prevent other fungi and bacteria from forming. Aerated cardboard is a great alternative to sawdust and doesn’t have to be pasteurized. Lastly, make sure you have enough spores to grow mushrooms. If there aren’t enough spores, you may not get enough clusters (the stage before the mushrooms form) to form mushrooms.

Quick Tips:
  • Used coffee grounds from same day
  • Choose a good drying substrate (cardboard, pasteurized sawdust)
  • Keep the mixture damp but not soaking wet
  • Use lots of spores (at least 10% of the entire mixture)

oyster mushrooms in a bottle
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Cardboard Method of Growing Mushrooms

One of the easiest and best ways to grow mushrooms is using the coffee-cardboard method. It doesn’t require pasteurization, so there aren’t extra steps in addition to the directions on growing.
Prep Time20 mins
Active Time10 mins
Waiting Time19 d
Total Time19 d 30 mins
Keyword: cardboard method, coffee grounds, growing mushrooms

Equipment

  • Clean Juice Container or Tall Plastic Food Container
  • Scissors
  • Cardboard
  • Plastic Bag
  • Mixing Container

Materials

  • Rubbing alcohol
  • Oyster mushroom spores
  • Freshly used coffee grounds

Instructions

  • Rip up cardboard in small pieces (about the size of a quarter), then soak it in filtered water for at least 20 minutes. Although the cardboard may have bacteria in it, the spores should take over if there are enough spores in the mixture.
  • Sterilize everything, including the juice bottle/container and mixing container. This will help prevent stronger bacteria from forming, which will steal the nutrients in the substrate.
  • Cut the top of the juice bottle where the cap is—skip this if you are using a plastic food lid. Then poke 3 to 4 holes at the bottom of the bottle or container for humidity and airflow. DO NOT THROW OUT THE TOP.
  • Add a few chunks of cardboard to the bottom of the bottle/container, then create the mushroom substrate by adding the cardboard with the used coffee grounds in a separate container. The coffee grounds should be warm, damp, and moist, but not soaking wet.
  • Add some spores to the mixture but keep some on the side as well. You want around 8-10% of the entire mixture to be the mushroom spores. But, if you’re unsure, add a little more.
  • Put a small 1-inch layer of the mixture on the bottom of the juice bottle/food container, then place a layer of spores. Repeat this step with the last layer being coffee and cardboard.
  • Put the juice bottle top/container lid back on. This traps the moisture - it’s okay if there are gaps from where you cut. If you used a plastic food container, place the lid back on.
  • Put a grocery bag or big freezer bag over it. If there is too much moisture and everything is wet and not damp, cut a few holes in the bag.
  • Place the container in a dark, cool place, but NOT the refrigerator. Mushrooms love wet, dark places, so think about that as you grow them. Try to replicate exactly how they grow in the wild.
  • Wait- in one to two weeks, the mushroom roots will start to form (mycelium) Check every other day to make sure there is moisture. Add moisture by spraying the lid or juice bottle top, as well as the plastic bag. Check for mold or any bacteria—throw it away and start over if there is any mold!
  • Once mycelium forms, clusters will start to grow. Cut holes in the plastic food container to allow the mushrooms to grow through, or remove it if you can successfully control the moisture. For juice bottles, take off the top.
  • Put the container in warm, indirect sunlight. Punch around 25 holes in a plastic bag and mist it, creating a mini humidity bubble around it. The holes help aerate the bag without losing moisture.
  • In around 4 to 5 days, you’ll have oyster mushrooms! Once you understand the growing process, you can grow them in virtually any container.
  • Sanitize every single place that the mushroom spores have touched, just in case.

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Conclusion

Mushroom growing is a great way to produce your food, while also learning a little science and cultivation. Using spent coffee grounds is a great way to recycle, while also skipping the pasteurization step for your mushroom substrate. You can even get creative with growing mushrooms and grow them in a terrarium, so it can turn into a mini hobby as well. As long as you have some same-day used coffee grounds and a little patience, you can start growing mushrooms with ease.


Featured Image Credit: thanhlocpham, Pixabay

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Jaimie Wisniowski

Jaimie is a freelance writer fueled by coffee, whether it’s hot, iced, or made from a local coffee shop. She enjoys writing all things coffee, especially if it means trying the latest coffee shop trends (hello cold foam!). After spending years writing poems, college essays, and short stories, it only a matter of time to turn writing into a career. Writing about coffee simply combined two of her favorite things! When she’s not drinking coffee by the minute and writing at her laptop, Jaimie spends time hiking, exercising, and living an active life. She also loves to snuggle up with a good book and her dog, Margo. If you catch her without a cup of coffee, she’s probably on her way to the coffee maker now.

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