The Truth About Coffee Grounds in Your Garden

by Michael Nolan on 16 February 2012 · 22 comments

in Articles

My Earth Garden: Coffee Grounds
Even among garden authorities, there are commonly-held misconceptions about coffee grounds and their use in the garden, but their origins are easily understood.  Coffee is an acidic drink, so it makes sense that the coffee grounds would likewise be acidic.

Only it isn’t true.

In fact, coffee grounds are generally close to pH neutral (between 6.5 and 6.8).  As it turns out, the acid that is contained in coffee is water-soluble, so the acid is essentially washed out of the grounds when coffee is made, which is why you need an acid reducer but your coffee grounds don’t.

Coffee grounds are still an excellent addition to your gardening routines. By volume they are about 2% nitrogen and they are noted as a good source of nitrogen for composting, given that they have the same basic carbon to nitrogen ratio as manure (20:1). The addition of coffee grounds to compost helps to raise and maintain a higher temperature in the compost pile for a longer period of time, which aids in killing pathogens that may be present.

Contrary to what some garden experts say, you might want to resist the urge to add the grounds directly to your garden though, unless you are using a nitrogen-rich fertilizer as well. In short, you can add coffee grounds to your compost to increase the nitrogen content, but when adding grounds directly to the soil, a nitrogen-rich fertilizer must also be added. This is because the grounds encourage microbial growth in the soil, and those tiny microbes are nitrogen-hungry wee beasties that will deplete the existing nitrogen.

Here’s what you need to know:  The truth is that many experts have been mistaken for years about the use of coffee grounds in the garden. Coffee grounds are not terribly acidic and they are not a good direct soil additive without additional fertilizers. Coffee grounds are however a great addition to compost, where their nitrogen content can be fully realized and used.

So by all means, save and use your coffee grounds, but do so with the benefit of science behind you. Talk to local coffee shops and ask about collecting some of their spent grounds for your use. Your compost will love it and so will your garden – eventually.

EDIT: I wanted to add a link to this story in which the author created compost using nothing more than coffee grounds and shredded newspaper. The chemical analysis of the finished product might surprise you.

Source:
Oregon State University Extension Service, “Coffee Grounds and Composting” [PDF]

{ 18 comments… read them below or add one }

Corner Garden Sue February 16, 2012 at 5:37 pm

I enjoyed this post. Thanks for the information.

Velva February 16, 2012 at 8:03 pm

This was a great article. I have a habit of sprinkling coffee grounds directly in my garden. After reading this article, I will be placing my coffee grounds right into the compost pile.

Velva

Tony February 20, 2012 at 6:50 am

I’ve always known this to be true,coffee grinds do in fact lose their acidity when brewed. Adding the grinds to the compost pile does in fact seem to help with the decomposing of your compost pile.

Emmon February 21, 2012 at 9:19 pm

This is a wonderful article that really dives a bit deeper than anything I’ve read before on coffee grounds as plant fertilizer. (I’d always figured you could just dump grounds round your plants! Maybe not!)

Catherine February 22, 2012 at 3:48 pm

Good info. I placed a link on our FB page – https://www.facebook.com/pages/Plumes-et-jardins/136647976354101 – And, as offered a while back during the food stamp challenge, if you would like to organize a draw among your readers, I would be happy to offer seed packets for edibles to the winner or winners. With spring just around the corner, this might be a good time. We can offer up to 20 packets of heirloom / open pollinated seeds.

Michael Nolan February 22, 2012 at 3:58 pm

Thanks, Catherine. Email me and we’ll work out the details. michael nolan at gmail.

Kathy Stanford February 24, 2012 at 5:28 pm

I put them in my compost and my worm bin. The worms love them!

sower February 25, 2012 at 8:28 am

I tried it on my roses but they couldn’t sleep well at night..switched to decaf..

Michael Nolan February 25, 2012 at 9:49 am

step away from the espresso!

Michael Nolan February 25, 2012 at 9:50 am

I’ll be doing that soon as well. Will be talking about worms and vermiculture on the site.

Kasey February 28, 2012 at 8:22 pm

Good to know! I had been adding them to my blueberry plant hoping it was adding acid at the same time as mulch. I’ll stop doing this now.

Arkady March 30, 2012 at 2:03 pm

Slugs and snails really don’t like coffee grounds; makes a great, natural, eco-friendly slug deterrant for strawberry plants!

Joan Weytze July 8, 2012 at 11:53 am

I’d heard that the smell of coffee grounds confuses and repels some insect pests. My zucchini leaves had many holes in them this year, which stopped after I applied a small amount of the grounds. I’ve also noticed that the rabbits stopped visiting my garden! Perhaps the trick is to top-dress in moderation. The rest of the coffee grounds go into my compost pile.

Steph W July 16, 2012 at 8:45 pm

I’m still confused because I’ve heard those pH tests are neutral only if you compost w/ the grounds and have a blend of other stuff in there, otherwise the grounds are way too acidic for the soil.

Michael Nolan July 16, 2012 at 8:46 pm

That is incorrect.

Beverly Anderson August 15, 2012 at 5:03 pm

Love what your doing here, nice photos and great info….Keep up the good work.

Leah November 15, 2012 at 10:43 am

I added the coffee grounds (without the added fertilizer) to my avocado plants and they took off growing. However, I now also have gnats breeding like they are going extinct! Great article and thanks for the info!

Barbara Votrobeck May 29, 2014 at 11:02 am

I’m glad we read this. I’ve been putting the grounds on our potted plants outdoors for the past two weeks; one 12-cup basket per pot. Noticed this morning that the leaves on our petunia are turning light green. Thus, I’ll need to add nitrogen-rich fertilizer to those pots.

Now to get this on Pinterest where I posted another article about the benefits of adding coffee grounds to the soil.

Thanks!

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