Composting Coffee Grounds


Of Mice and Mountain MenI drink a lot of coffee; probably too much coffee, but that’s another issue. As a result of my coffee habit we have a steady supply of coffee grounds to dispose of. Coffee beans are a plant, why not compost them along with the rest of my kitchen waste? And that’s what I do.

Advantages of Composting Coffee?

  • Since the beans were harvested live, even though they have been roasted and ground up they are considered a “green” element of compost and a nitrogen source: C/N ratio about 20:1.

  • Worms love coffee, probably for reasons similar to our own. Coffee is related to the cocoa bean and contains many of the same nutrients, most of which are not leached away to the brew we drink. Those nutrients are retained in the grounds, for the most part, and worms love them. Some vermicomposters use a coffee-rich mix with their worm beds.

  • Unlike purchased manure, coffee grounds do not contain pathogens or weed seeds. If you use manure from your own animals you know what went in one end so you have a better idea what’s coming out the other. With most commercial manure, you don’t. Weed control chemicals and fertilizers used on a pasture can create problems in your compost. Even feed grain that has been tinkered with can hold residuals that will mess with your crops.

  • Their pH buffering effect (discussed below) helps prevent pH spikes in either direction due to variable compost components.

Coffee Grounds to Compost

Are Coffee Grounds Acidic?

One of the issues I’ve seen bantered around is the question of pH acidity in coffee grounds. Some folks claim they are quite acidic and should be used only with acid-loving plants like asparagus and berries. Others dispute that. Who is right? One of the forum regulars with a scientific background did some controlled chemistry experiments on the acidity question and this is what he had to say:

"Roasted coffee is fairly acidic, but it appears that almost all of the acid is water soluble and is extracted during brewing. Used grounds have essentially neutral pH, although the coffee beverage produced is rather acidic. The measured pH of used coffee grounds was 6.9, with a significant amount of buffer capacity – adding the coffee to either acidic or basic solutions drove both towards neutral pH. The exact pH of used grounds will depend on the pH and alkalinity of the water used in brewing, but with any potable water, used grounds will be close to neutral pH."

4/29/2016 8:37:06 AM

Hi, Mary from Old Dog New Tricks. I posted about coffee grounds from Starbucks some time ago, but your post is far more in depth. Good job. I have an idea about pouring on liquid coffee. Do you remember how years ago, people just added more grounds to the old each day. I tried it and it is terrible! However, maybe you could use the old in your maker to get the liquid you need! If it made me cringe, maybe it would also make the critters cringe! Just a thought! I put the used grounds around the base of my fruit trees when the fruit is on to keep the ants from crawling up. Also at the base of the bee hive for the same reason. Didn't keep the bees from returning.

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