Putting Coffee Grounds to Good Use

Billions of people around the world drink coffee every single day. Agriculture and Agri-food Canada estimates that 14 BILLION cups of coffee are consumed each year in Canada! Assuming that each cup takes about 25 grams (1 heaping tablespoon) of ground coffee to make, it takes 350 million kilos of coffee to fuel our days (and nights!). Most people just throw out the used grounds, which contributes a significant amount of waste to our ever-increasing landfills. However, used coffee grounds are actually a highly productive ingredient for plants and gardens.

Photo from blogto.com
Photo from blogto.com

Here are some useful characteristics of used coffee grounds. They are:

  • High in nitrogen (a very valuable nutrient for plants). Grounds have a C/N (carbon:nitrogen) ratio of 20/1.
  • Almost neutral (although coffee is highly acidic, the pH level of the grounds are diminished significantly when brewed)
  • Digestible by worms
  • Good for improving soil tilth (structure)
  • A natural pesticide (great for repelling slugs, flies, and other critters!)
  • An agent for bacterial control. The natural mold and fungus on coffee can suppress pathogenic fungi, including fusarium, pythium, and sclerotinia species.
  • Weed killers

Considering all these properties, used coffee grounds are perfect for your gardening practices! What better way to recycle consumption “waste” than to use it as a growing agent :)



When added to a compost pile, used coffee grounds injects a healthy dosage of nitrogen into the equation, a nutrient that is absolutely essential for plant growth. They improve the quality of the soil and foster the growth of certain microorganisms, which help to break down substances in the soil into elemental forms that can be absorbed by plants.

If you add used coffee grounds to your compost pile, make sure to add an equal amount of some carbon source, such as shredded paper (unbleached and unprinted) or dry leaves. Doing so helps balance the pH levels, since coffee grounds are slightly more acidic than neutral. Mix well!



Photo from rajputagro.com
Photo from rajputagro.com

Coffee grounds are also great to throw into worm bins! Vermiposting is an excellent way to turn compost and organic matter into nutrient-rich food for plants. For some reason, worms are very attracted to coffee grounds and can break them down well. Remember that there should also be an equal amount of shredded paper or leaves (newspaper is also okay for vermiposting).



Photo from ficksupply.com

In addition to adding coffee grounds to your compost pile, you can add them directly on or into the soil for added benefits. Used in this way, coffee grounds can act as a natural slug and bug repellent (crawlers don’t seem to like the abrasiveness or the caffeine in the grounds).

The microscopic world is filled with organisms constantly competing for space and food. Since coffee grounds breed specific types of fungi and bacteria, they also prevent the growth of pathogenic fungi that can harm your plants.

You can spread the coffee grounds directly onto the soil as sheet mulch and cover with leaves and compost. All you need is a half-inch layer in any one area.

You can also make a liquid fertilizer by steeping 2 cups of used grounds in 5 gallons of water for 6-12 hours. Use it to water or foliar feed your plants.

*Important to note: the slight acidity of coffee can actually inhibit the growth of certain plants, such as alfalfa, white and red clovers, Chinese mustard, komatsuna, geranium, and asparagus fern. However, it’s fantastic for the growth of leafy greens, fruiting vegetables, fruit trees/bushes and sugar beets. Remember to first look up the properties of the plants in your garden!


Growing mushrooms

Photo taken by Ron Mahan
Photo taken by Ron Mahan

Best of all, coffee grounds are the PERFECT substrate for growing mushrooms (most notably oyster and shiitake mushrooms)!

Typically, growing mushrooms takes a long time and a lot of trial and error. It relies on significant equipment for pasteurization and climate control (or an ideal outside growing environment). The most common growing mediums are freshly cut logs (can be quite unreliable and unpredictable) and pasteurized grains, such as straw, millet, and rye. Grains have to be pasteurized so as to kill off resident microorganisms that will compete with your chosen fungi.

Conveniently, used coffee grounds are already “pasteurized” by the brewing process so you can go straight to inoculation! (Inoculation = reproduction of an organism in a substrate material)

Different species of mushrooms take different lengths of time to grow. The easiest and quickest one to grow is the oyster mushroom.


So what do you do?

Photo by Simone Schoutens
Photo by Simone Schoutens

You will need:

– 2.5 kg of used coffee grounds and 0.5 kg of spawn (oyster mushrooms) to produce about 1.25 kg of mushrooms
– A plastic bag, container, or ideally a filter patch grow bag (at least 2L)
– A clean mixing bowl
– A warm and dark place to store your bag/container

If you are NOT using a filter patch grow bag, cut 4 x 5mm holes in the sides of your bag/container.

Mix the spawn and coffee grounds well in the mixing bowl. Make sure that spawn is broken up and distributed evenly among the coffee grounds. Then, put the mixture into your cultivation bag/container.

Place in a warm and dark space (64-77 degrees Fahrenheit, 18-25 degrees Celsius).

During the next three weeks, you will see the spawn grow white fibers everywhere. These white fibers are called mycelium; they will spread throughout the coffee mixture and break it down the grounds to use as food.

If there are spots of green, that means there is a competitor mold. You can kill off small patches of mold by adding a pinch of salt to the infected area. If the entire bag is green though, it’s a lost cause. You just have to start all over again.

After three weeks, the entire bag/container should be completely white! Now, place it in a spot with plenty of fresh air and some light. Cut a 5cm x 5cm hole in your bag/container. Spray TWICE daily with water, making sure not to let it dry out. Why? Mushrooms LOVE damp, dank, but not too wet, spaces.

In another week, little mushrooms will start bursting out of the hole. They will double in size almost every day until they fully ripen, which is when the edge of the caps start turning upwards. At the end of 5 weeks, you should have about 1.25 kg of mushrooms that are ready to be harvested!

Note: Coffee grounds do NOT go bad! You can keep them in a container for long periods of time. Additionally, mycelium stay nicely in a closed container and do not bloom until you start watering it, so you can leave one sitting around for months.



If you don’t drink coffee, just ask your local coffee for their used grounds! Most would be more than happy to give them to you, since they already pay high premiums to waste disposal services and companies. Using coffee grounds to grow mushrooms or to add to your compost/garden are effective ways to minimize waste; plus there are the additional benefits of growing your food more productively. There is no “waste” in nature – one organism’s byproduct is another’s food or it can be broken down to provide key nutrients. Although our coffee consumption has helped fuel an industry that creates an unimaginable amount of waste, we can help alleviate the problem by acting as much as possible in line with the laws of nature.

Recent start-ups such as Back to the Roots (https://www.backtotheroots.com/), and Fungi Futures (http://www.fungi-futures.co.uk/) are setting a great example for taking this kind of initiative. Based in Oakland, California, Back to the Roots collects the used grounds from coffee shops and packages the coffee/spawn mixture into a neat little box for people to buy and grow mushrooms at home. Fungi Futures does the same thing in the UK. Creating the right proportion of grounds and spawn (or spore) can be a tricky process, so these ready-made kits are a greater introduction to doing it yourself.

Photo from backtotheroots.com
Photo from backtotheroots.com

Now, a burgeoning initiative called Champignons Maison is raising money to do be able to do the same in Montreal! Check out their campaign at http://www.indiegogo.com/projects/champignons-maison-offres-de-lancement and consider donating to this project. The reward levels are extremely reasonable and you’ll receive your own mushroom growing kit!

Try growing your own mushrooms! It’s easy to start eating locally, one mushroom at a time. Maybe it’ll inspire you to start recycling coffee grounds from not only your own home but also the rest of your city. Let’s take those 350 million kilos of grounds used every year in Canada to grow our food!


Sources and recommended reading








http://live.wsj.com/video/grow-your-own-mushrooms-in-used-coffee-grounds/866C279A-1CFF-41CC-B73A-7798C6761C67.html#!866C279A-1CFF-41CC-B73A-7798C6761C67 (Video)

http://www.youtube.com/watch?v=29_QsMAdZCM (Video)

http://www.youtube.com/watch?v=42Imc1KTgXc (Video)

5 thoughts on “Putting Coffee Grounds to Good Use”

  1. We always composted when I was a kid. Everything from old coffee ground, vegetable peelings, eggshells, ect. We kept a pile by the back door step and transferred it to a larger area and added horse manure. It is rather a lost art here in the US. If you build a shelter around it, it will actually give off heat. We used an old metal barrel.

  2. Genius, all of it, all of you! As a Vermonter now stuck in RI being stale, I am seeking land/communal friends to join in with to build a home and community ASAP. Homeless by economic debacle forces me and my multi talented building skills to join with others in sustaiing some sembelance of balance and quality of life! Carry on New World Warriors!

  3. Perhaps regular brown 1 inch slugs are repelled by coffee grinds, but while in British Columbia we found their jumbo 2-3 inch lime green slugs came running when we put the grounds near our site before carrying them to the bin. The filter would be crawling with 3-4 slugs within minutes!

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