Can I Put Coffee Grounds in My Composting Bin?

Every day you throw away used coffee grounds in the trash and wonder if there’s a better way of disposing of them, such as composting. You know other kitchen scraps can be used to help your garden’s soil be rich in nutrients, but can you add coffee grounds to your composting bin?

Coffee grounds are an excellent addition to any compost bin and add many great nutrients to your bin and soil. Because they are finely ground, they can easily break down at a fast rate. 

Let’s look a bit deeper into why coffee grounds are so great for composting and if other coffee-related materials can be composted as well.

Why Are Coffee Grounds Good For Composting?

Compost is designed by nature to release many nutrients slowly over time, making it highly beneficial to all sorts of plants. Although any pile of kitchen and yard waste will decompose over time, adding the right materials in the right proportions will speed up this process tremendously.

Every successful compost bin or pile contains green material and brown material. The combination of the two materials help the compost break down and nutrient rich.

Coffee grounds are high in Nitrogen, so they are considered the green material in your compost bin. In addition to Nitrogen, they contain other minerals including potassium, phosphorus, and small amounts of calcium, copper and magnesium.Composting is great for our environment. You’re taking material headed to the landfill and turning it into rich nutrient soil.

Think of all the coffee grounds thrown away each day in homes and coffee shops. I knew someone who would pick up used coffee grounds from a nearby coffee shop and use them in their compost bin on a fairly massive scale.

Below, is a table of some items that are considered “green” and what is considered “brown.” Both are essential to the composting process.

Coffee Grounds are the green material in a composting bin. Table compares green and material used in composting. Green material is good for nitrogen and includes coffee grounds, vegetable and fruit peelings, and yard clippings.
Brown material is good for carbon and includes cardboard, sawdust, paper shredding's, and dried leaves and twigs.
Table of Composting Material

How to Use Coffee Grounds in a Composting Bin and Garden?

Whether you are wanting to boost the growth in your garden of carrots and radishes or beautiful hydrangeas, adding rich soil will act as a fertilizer.

You may already have your compost started in a pile in the backyard or a bin. If so, then great! You’re on your way to rich nutrient soil. If not, let’s go through a quick and easy-to-follow tutorial on how to get started.

First, decide where and how you wish to compost. I started by simply clearing a large area at the far end of my yard. I prefer digging a wide shallow hole to start and begin layering my green and brown material in it.

If you wish to keep your compost in a bin, you can either use an old trashcan or purchase a simple one from Amazon. A friend of mine uses this one and recommends it to people just starting out composting. It’s inexpensive, 100 gallons, and is designed with ventilation holes.

If you can spend a bit more money, around $100, I recommend an Outdoor Tumbling Composter Dual Rotating Batch Compost Bin. These tumblers take much of the work out of typical compositing and prevent wildlife from destroying your piles.

I also recommend purchasing a pitchfork for turning and aerating if you don’t already have one.

How to Compost Coffee Grounds

Once you’ve decided how you are going to compost, go through the steps below to add your coffee grounds to the compost.

  1. Layer your coffee grounds (green material) with your brown material (dead leaves, shredded cardboard, sawdust). A good brown, green balance is the ratio of green and brown material necessary for good decomposition. Microbes do their best with a carbon to nitrogen ratio of 30:1.
  2. Spray a bit of water between layers to maintain good moisture levels in your compost bin.
  3. Once all your materials are layered in the bin, depending on what you use to compost will determine your next steps.
  4. IF USING A PILE or BIN: Thoroughly mix all material. If the pile is looking too dry, add more water. Add some brown material if the pile seems too wet and soggy.
  5. IF USING A TUMBLER: Close the lid and give a few spins. Let sit for a few days and spin again. Add more water if it starts to look dry.
  6. You can always add additional coffee grounds once the compost pile has started. Just be sure to add enough brown material to prevent soil that is too rich in Nitrogen.
  7. Continue to check and mix your compost bin every week until your compost materials are disintegrated, and you have nice earthly-smelling dirt.
  8. This process usually takes anywhere from three to six months.
  9. Sprinkle around your flowers, vegetable gardens, plants, and trees.
  10. Watch your flowers, vegetables, and plants grow!

Composting can take a fast as two weeks or up to two years to be full completed. To learn more about how to start a compost, click here.

TIP: Try to add equal amounts (in volume) of coffee grounds/green material and your brown material. But remember, once your compost pile begins the process of decomposing the material, you can be the judge and determine if you are low or high on either green or brown material.

Can You Put Too Much Coffee Grounds in a Composting Bin?

Yes, you can put too many coffee grounds in your compost bin. The result of too much coffee grounds is high levels of Nitrogen in your compost. These high levels cause the release of ammonium gas and create a foul odor.

To be more precise, coffee grounds should only make up between 10 and 20 percent of the total volume of the compost.

In addition to high nitrogen levels, adding too many coffee grounds to your compost can decrease the number of earthworms in your pile or bin. These worms are very beneficial to your compost and can assist in the process.

To remedy high nitrogen levels, add some brown material, such as shredded cardboard, dead leaves, or sawdust. This will balance and dilute the strong chemicals in the grounds and lessen the effect on the worms.

Signs Your Compost Needs More Brown Compost Material (Carbon)

  • Overheating: The optimal temperature for a compost bin is between 135 and 160 degrees Fahrenheit. If it gets above 160 degrees, the organisms and bacteria needed in decomposition are not able to do their job; thus, leaving you with a pile that is doing nothing. In addition, if it heats up too much, your compost can catch fire! If you find your compost bin above this temp, turning or aerating will help release the heat. Then add some more brown material and water to the bin.
  • Smells of Rotten Egg or Sulfur: This is a byproduct of hydrogen sulfide due to insufficient air circulation and oxygen. To fix, aerate regularly and add some brown material like small sticks to help create air pockets.
  • Smells like Ammonia: Ammonia smells result from too much Nitrogen (coffee grounds or other green material). By adding additional brown material, you are adding extra carbon to balance out the excess Nitrogen. Continue to aerate and turn to help release the excess Nitrogen.
  • Slimy in Appearance: If your compost pile looks too wet and slimy, you need more carbon materials (brown materials).

How to Know if More Green Material its needed in the Compost

Now that we’ve discussed the problems that arise when your nitrogen levels are too high let’s look at when your carbon levels (brown material) are too high.

When your compost bin contains too much brown material and not enough green, you’ll notice the temperature inside the pile is not high enough for microbes and bacteria to do their work. Thus, creating an environment where decomposing cannot effectively take place.

Remember, the Nitrogen rich material, like coffee grounds, is what will increase the temperature of your pile. To counteract the carbon-rich materials, you’ll need to add nitrogen-rich materials.

Signs Your Compost Needs More Green Compost Material (Nitrogen)

  1. Pile temperature too low: As mentioned earlier, the optimal temperature for decomposing is 130 to 160 degrees Fahrenheit. The temperature is too low if your thermometer reads below this range and you don’t see some steam coming from your compost bin. Add some coffee grounds or other green material to the pile and mix.
  2. Material isn’t decomposing: The only reason to do a compost pile in the first place is to decompose kitchen and yard scraps to make nutrient-rich soil. So if the materials are not decomposing, there is definitely an issue. If, after a week, you don’t see any change in your pile, add some more green material to it.

Do All Plants Like Used Coffee Grounds?

Adding coffee grounds straight to the soil should only be done with research and caution. Since coffee grounds are more acidic, they can alter the ph of the soil. Some plants will not do well if the soil ph rises.

Acid-loving plants include blueberries, azaleas, and hollies. On the other end, the growth of asparagus fern and geraniums will be stunted if coffee grounds are directly added to the soil. 

Although, once the grounds break down and decompose with the compost, they become less acidic and eventually closer to a neutral ph. 

Should You Add Worms to the Compost?

You may have heard that adding worms to your compost will help it decompose faster. Adding worms, primarily red wigglers, to your pile can be beneficial but isn’t necessary. Some people maintain a worm bin just for this. Either way, your compost will decompose over time. 

If you have a pile in your backyard, worms and other insects will find their way to it without any help. As the worms eat the items, it goes through their digestive tract and out the other end, known as casts. The digested compost typically is higher in nitrogen, bacterial and organic matter. 

Do Coffee Grounds Keep Insects Away?

Coffee’s natural acidic properties make it a great natural pesticide, repelling all sorts of bugs, including slugs. Slugs hate these acidic properties. If you ever have an issue with these insects, put coffee grounds down to make a barrier. 

The Environmental Protection Agency suggests burning the coffee grounds before using them as a repellant to increase potency. Place on a flat surface outside and burn as you would incense.

Besides slugs, other bugs, including wasps, bees, mosquitoes, ants, and flees, are also turned off by the smell of coffee grounds. You can toss out those toxic bug sprays and use your old coffee grounds to keep the bugs away!

For more uses of used coffee grounds, click here.

Can Other Coffee Items be Added to Your Composting Bin?

Another coffee item that can be added to your composting bin is paper coffee filters. If you are going to add these to your bins, I recommend buying the unbleached filters. While many speculate that the bleach in the white filters dissipates by the time the compost is ready for use, some still worry it poses a threat.

So, I aire on the side of caution and use the unbleached filters.

Also, check out our other article, “Can You Reuse Coffee Filters?”

Can Coffee Grounds be put on Your Lawn?

Used coffee grounds can be used as fertilizer for your lawn. The nitrogen, phosphorus, and other minerals are slowly released into the ground to help your grass grow thicker and greener. 

Placing coffee grounds on your lawn also makes the earthworms happy. They enjoy eating the grounds, digesting it, and excreting it, known as casting. The casting improves ground aeration and stimulates impressive lawn growth and health. 

Final Thoughts

To summarize, used coffee grounds are excellent for your composting bin, as they are rich in nitrogen. Ensure that your brown or carbon material is added in adequate proportions to prevent over or underheating and smells.

Now, get to composting!

For more great alternatives to using coffee grounds, check out our other article, “8 Things to do with Coffee Grounds.”

8 Things to do With Coffee Grounds

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