I am addicted to using coffee grounds in the garden. Every week, I am a regular at the coffee ground bin at Starbucks. I feel like I am at Cheers and everyone knows my name. (Oh, come on, you remember Norm.)
Just to give you some background, my sickly roses miraculous perked up after a round of coffee grounds. And the love affair began. But, I began to worry that my new found obsession may not be the best idea for my plants. Sometimes a good thing can be too much. (How many of you saw Fatal Attraction?)
I was afraid I would have to quit cold turkey after my friend told me to be careful. She said I should not give the plants too much coffee grounds. What happens if she was right? (*Gasp*) How much is too much?
Searching for the Coffee Grounds Guidelines
I started to dig (sorry about the pun) to find if there was a university study on the effects of coffee grounds on plants. At first blush, I only found articles written from gardeners or DIY’er reporting the same things I knew. No one seemed to answer the question of “how much.” The research was quite frustrating.
All, I wanted to know could I use coffee grounds in the garden. Is that too much to ask?
Gardens Alive Takes on Coffee Grounds and Plants
I stumbled upon an article on Gardens Alive answering a question from someone in New Jersey asking the effects of coffee grounds on plants. (And no, this wasn’t my question.)
Gardens Alive had coffee grounds tested by Will Brinton, founder and Director of the Wood’s End Research Laboratoryin Maine. He found the grounds were too acidic, even for acidic loving plants. He also cautioned the grounds should not be added to the soil in raw form. However, he did like them for compost.
“Will liked my [Garden’s Alive] suggestion of four parts shredded leaves to one part grounds by weight, but adds that even having grounds make up 10% of a pile of otherwise shredded leaves would create great compost.”
Well, that article definitely was a downer for me. (Okay, it was a kill joy.) It seemed that I can only use the grounds for composting.
To add to the confusion, another gardening article I read called coffee grounds “brown matter.” Boy was I confused. So, if I followed Gardens Alive’s advice to add leaves to my coffee grounds, would I have to supplement with more “green” material for my compost?
This can’t be this complicated.
Rodale Institutes’ Respond to the Coffee Grounds Dilemma
I reached out for Rodale Institute since it was more likely they would have an answer for me. (If the name, Rodale Institute, sounds familiar to you, it is because many of you may know the name through the magazine, Organic Gardening, one of my favorite gardening magazines.)
Luckily I connected with Dr. Paul Hepperly, the research and training manager at the Institute, who is a well known authority in organic agriculture. Surely, he would know. (Fingers crossed.) He explained that once the coffee grounds are added to the soil, they start to decompose, and in turn, their acidity neutralizes. Ultimately, they are only adding nitrogen to the soil.
Best Practices for the Use of Coffee Grounds in the Garden
His suggestion was to side dress the plant with no more than one inch at a time. He further caution to not add more grounds until the original grounds had decomposed. Coffee grounds are solely a soil amendment and not a fertilizer.
He further explained that soil should have an organic matter of five to eight percent. At some point, there is a diminishing return if you keep adding coffee grounds, and you soil has already reached the eight percent threshold of organic material. It will not hurt the soil, but may not help much at that point. It is best to take a soil sample during the year to see what your soil needs.
As for compost, he suggested one volume green material to three volumes of brown. Coffee grounds are viewed as “green” material. (Whew. I was relieved that this matter was settled.)
What about using coffee grounds for composting? Read on my final segment on using coffee grounds for compost.
Don’t forget to check out all of my other gardening posts! If you are here reading about coffee for your plants, you must love to garden.
Join the Conversation:
- Have you used coffee grounds in your garden? If so, what was the result?
- Have you put coffee grounds in your composter? If so, what was the result?
- Do you think the grounds are too acidic and don’t use the grounds in your garden?
- What common household item do you use in your garden?
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