Using coffee grounds for plants has advantages and disadvantages.
Many plant lovers who drink coffee are using coffee grounds as a fertilizer and to add to compost. But there’s confusion on when, where, how — and whether — to use coffee grounds for best results.
If you don’t drink coffee, there are options for easy access to lots of used coffee grounds via local coffee shops and restaurants. If we consider the widespread habit of drinking coffee, we can imagine the huge amount of available coffee ground resources.
Making Good Use of Spent Coffee Grounds (SCG)
Most gardeners love to recycle, upcycle and compost as much as possible, and coffee grounds are one of those items with fringe benefits. Even if it’s just one or two people in your home consuming two cups of coffee a day from fresh coffee grounds, the refuse of spent coffee grounds (SCG) can really add up over time.
We’re coffee fans and have added organic coffee grounds to our compost pile along with other organic matter for years now. We love how the coffee beans that create our favorite brew can go onto benefit our plants too! But we wanted to know more on using coffee grounds for plants and gardening.
So we started researching things like what plants like coffee grounds in the soil as fertilizer, and which plants don’t? And should we put the coffee grounds directly around the plants that like coffee, or should we continue putting the coffee grounds into the compost?
That’s what we wanted to know for sure. However, as we studied this topic of using coffee grounds for plants, we were surprised at what we found.
The deeper we dug into the info and research, the more we discovered the complexity of the subject. The more we learned, the more questions we developed.
It’s not as simple as a list of what plants like coffee grounds, and what plants don’t. When it comes to plants and plant ecosystems such as in the garden, what’s seemingly good for one thing could be compromised by another.
It’s a Complicated Relationship
It turns out that some of the research on using coffee grounds for plants runs contrary to urban legend. The relationship between coffee and plants is complicated, but we’re going to try to keep it as simple as possible.
So grab your cup of joe and let’s go!
Confusion and Misinformation
In researching this article, we found a LOT of content that was basically copying the same content over from other websites. Okay, so everyone’s saying it… it must be true, right? Haha… you know better too, don’t you!?
Yep, proliferation of content, doesn’t necessarily mean that it’s true, especially if it’s repeating the same misinformation.
We began our journey down the rabbit hole on using coffee grounds for plants because we kept finding conflicting information.
Some articles say never to use coffee grounds in the garden. Others say that coffee grounds are wonderful for plants.
Some lists of what plants like coffee grounds had exact opposite recommendations to others. In other words, one plant might show up on the “likes” list of one website and the “does not like” list on another. In addition, there was conflicting information on the acidity of coffee grounds, nitrogen benefits, caffeine detriments, and whether coffee grounds are a fertilizer, amongst other details.
Hmm… okay, this isn’t going to be a quick and easy article to write after all.
Time to Dig Into Scientific Studies on Using Coffee Grounds for Plants
Time to roll up the sleeves and cut through the noise and confusion. We like to go to scientific research studies whenever possible, and that’s where we found the most interesting, informative, and relevant information on this subject. Even though there was some conflicting information on some of the extension service articles, overall, we were able to glean the bigger picture to share with you here in this article.
In doing all that research, we also discovered several reasons for the confusion and misinformation on using coffee grounds for plants. We’ll list that shortly, at the end of this section or so.
So now that we’ve got it all sorted out, hopefully it will be much easier for you to read and heed for the best results for your plants.
But in gardening, as in life, learning isn’t a one-and-done. It’s an ongoing daily process, so if you have additional facts or personal experience to share, send it on, we’d love to learn from you too!
First, we wanted to know:
Are Coffee Grounds Acidic?
No, not really. Spent coffee grounds are NOT highly acidic.
Apparently, while coffee is an acidic beverage, used coffee grounds are not considered to be acidic. Many articles will say that coffee grounds are acidic, and some will say that they’re highly acidic.
However, that’s not true.
Research on pH levels of coffee grounds for plants and in the soil over time is they they are either mildly acidic or mildly alkaline, and any acidity declines to neutral over time and never affects the entire soil pH.
The reason coffee grounds are not acidic is because the acid in coffee is water soluble, which means that most of the acid in coffee ends up in your cup of coffee and not the grounds, and therefore not in your soil either.
The perfect pH balance is 7.0, with a mild mid range on either the acid or alkaline side of 6.5-7.5. Spent coffee grounds, also known as (SCG) in research studies, typically registers between 6.5-6.8 pH, and moves towards mildly alkaline over time.
“The pH of decomposing coffee grounds is not stable and one shouldn’t assume that it will always, or ever, be acidic.”
~Linda Chalker-Scott, Ph.D., MasterGardener WSU editor, Extension Urban Horticulturist[1]http://www.uwyo.edu/barnbackyard/_files/documents/magazine/2017/summer/plantsperk0717.pdf
Why Many Lists on What Plants Like Coffee Grounds Are Not Relevant
If you’re wondering what plants like coffee grounds, well, it turns out that it doesn’t really matter that much, which we will explain as we continue.
Most articles you’ll find on page one of Google listing what plants like coffee grounds and what plants don’t, are based on which plants are acid loving plants, and which ones are not.
It’s seems logical that since coffee is an acidic beverage, the coffee grounds would also be acidic. So the confusion and misinformation is understandable. However, as indicated above, that isn’t the case when it comes to spent coffee grounds.
Soooo… it doesn’t matter which plants do — or do not — like acid, because coffee grounds are essentially pH neutral.[2]https://extension.oregonstate.edu/gardening/soil-compost/coffee-grounds-composting
Now we have some new questions to ask and answer, which is what we’ll do next. Are coffee grounds good for plants, how and which plants? Let’s take these questions one at a time.
3 Easy Ways to Test Your Soil
If you need to test your soil, here’s three simple ways:
- Your weeds will reveal your soil health!
- Perform a simple soil sample test
- Ask the county extension service to test it for you, (that’s usually a free service).
So Are Coffee Grounds Good for Plants?
Yes… and no. We’ll start here with how coffee grounds are good for plants.
Coffee grounds do have nutrients beneficial to plants. But more than that, it’s that coffee grounds are good for the support systems that help plants grow.
Soil tilth is the structure of soil, and includes the consistency, composition, aeration and permeability of soil.
Benefits of Coffee Grounds in the Garden and Farm Crops
- NUTRIENTS:
- Proven to increase iron and zinc levels in the rice crops grown with coffee and tea waste[3]https://pubmed.ncbi.nlm.nih.gov/21547921/
- An organic plant supplement, but does not replace a good organic fertilizer
- WEEDS: Natural weed control for developing crops[4]https://www.tandfonline.com/doi/full/10.1080/1343943X.2021.2007142#
- DISEASE: Disease suppression during decomposition – coffee grounds in soil help suppress common fungal rots and wilts such as Fusarium, Pythium, and Sclerotinia, which typically affect:
- potatoes
- tomatoes
- peppers
- eggplants
- herbaceous plants
- succulents
- SOIL:
- Retain moisture in soil, (but only if applied as a thin mulch so as not to create a water barrier)
- Helps regulate soil temperature
- Improves soil tilth
- PEST DETERRENT:
- Gets rid of ants – based on comments from readers from their direct experience
- May get deter voles, moles or chipmunks (based on the observation of one gardener which you can read more about in this voles article)
- Some believe that coffee grounds may deter slugs and snails*
Coffee grounds help retain soil moisture.
*For mulch, we prefer