Do Worms like Coffee Grounds?

Amy Hyslop
Last Updated On August 7, 2022

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As a newbie worm farmer, I have invested significant time investigating the question ‘do worms like coffee grounds?’

I love coffee and consume copious amounts of it and often feel somewhat guilty about the amount of waste this passion produces. And so, the concept of being able to compost it via the worm farm is highly appealing.

I soon discovered that using coffee grounds for worms is a well-researched area. This article will discuss the important questions for vermiculture around coffee; do worms like coffee grounds? Can worms eat coffee grounds? And what are the effects of coffee grounds on worm farms?

Do Worms Like Coffee Grounds?

The Short Answer

The short answer is yes, worms like coffee grounds.

Just like you, they enjoy the flavor as well as the texture of used coffee grounds. This is amply confirmed by anecdotal evidence from a range of worm farmers and more technical arguments.

As an organic, worms eat used coffee grounds and often have quite the appetite for it.

However, all things in moderation, as it used to be said. Too much ground coffee can negatively impact the growth, maintenance, and effectiveness of your worm farm.

Do Worms Eat Coffee Grounds?

The Long Answer

To understand both why worms like coffee grounds and why moderation is needed, we need to get a little more specific and technical.

Coffee grounds impact your worm farm and population in a range of ways. These effects are both positive and negative.

Positive effects of coffee grounds for worms

Ground coffee holds water well, which can help keep the worm farm moist
Coffee grinds give the worms grit, which helps them better digest their food
Because of their high carbon ratio, coffee helps increase the temperature of a worm farm over winter
Coffee grounds are soft and so are easy for the worms to live in
Coffee grounds are a natural pesticide that can help ward off other insects

Negative effects of coffee grounds for worm farms

The high carbon to nitrogen ratio (20:1) can cause excessive heat, which can kill the worms
Coffee grounds are acidic, and so too much can raise the pH level above optimal
Coffee grounds can dry and form hard crusts or anaerobic clumps
Coffee grounds absorb liquid and so can help dry out a worm farm

As you can see, there is a bit of a love-hate relationship between worm farmers and coffee grounds. On the one hand, worms like coffee grounds and the gritty size and texture is beneficial for the worms.

Similarly, the nutrients in coffee beans are great for the vermicompost produced. In fact, there have even been researched academic studies showing that the addition of coffee grounds enhances the quality of the worm castings produced (1).

However, too much and you can dry out the worm farm, spike the pH level, or cause a detrimental rise in temperature. So do worms like coffee grounds? Yes, absolutely, but too much can be harmful to them.

How much coffee grounds for Worms?

So the question becomes, how much coffee grounds should you add to your worm farm? And the answer depends on a range of factors; how many worms you have, what size your worm bin is, and what other foods you add.

However, as a general rule, make sure that coffee grounds do not form more than 25% of the worms’ diet. So every time I add other foods to the worm farm, I will usually mix them with some coffee grounds for the reasons adduced above.

I would not advocate picking up coffee grounds from your local cafe in a domestic closed system (that is a plastic worm farm). This can work well for midsize to large commercial worm farms but is excessive and more likely to do harm than good in a home setting.

Tips for adding Coffee Grounds for Worms

A few tips are helpful to be aware of if you intend on making coffee grounds a regular part of the worms’ diet.

Always put the coffee grounds in wet, not dry – I used to add my coffee grounds dry, but this soaks up important moisture in the worm farm and makes it more likely to irritate the worm’s skin and cause crusts to form.
Do pocket feeding – Pocket feeding is where you place food in certain parts of the worm farm rather than over the whole thing. This means the worms can go for the coffee grounds or leave them, giving you an indication of how much is too much.
Leave them to go moldy in a bucket – This one might seem counterintuitive but is actually a proven practice among worm farmers. Leave the grounds in some water outside for a few days, and bacteria will grow, which aids the worms.

Do Worms like Coffee Grounds? -The Summary

In summary, yes, worms like coffee grounds and consume them happily.

Positively, the coffee grounds hold water, are a great size and texture for worms, are a natural pesticide, and enhance the quality of the castings produced. Negatively, if used in excess, they can heat the worm farm and kill worms, increase the pH level, and dry out the worm farm.

So should you feed your worms coffee grounds? Yes, absolutely, just do it in moderation, and you will be fine. Mix in with other foods; make sure you put them in wet, not dry, and your worms will love you for it.

Amy Hyslop

I am the designer and content manager of The Coffee Folk. I love going on adventures with the kids, tracking down the best cafes, and coffee at the beach.