Coffee Grounds, Garden Friend or Foe?

I was having problems with my roses. They were getting rust from getting their leaves wet from my sprinkler system. Last summer, they looked terrible so I cut them back and thought they would never grow back. I am new to growing roses…well growing anything so most of my planting experience is through trial and error and a lot of error. One day, my friend came over whose mom was a garden maven. After looking at my roses (or what was left of them), she said “sprinkle coffee grounds around them and they will flourish.” I was desperate because my roses looked so pathetic. I started taking my husband’s left over coffee grounds and sprinkling them around the roses and sure enough they started to grow. I was amazed!

This year, Starbucks moved into a neighboring town. Since my husband was my family’s only coffee drinker, I did not have enough grounds to give my other plants. Figuring that Starbucks had coffee grounds and probably would not mind giving them away, I went into their store. Well, they beat me to the punch and there in a wastebasket next to the door was a little sign “Grounds for your Garden”. I took their package and left home with my garden treasure.

I had no idea how much coffee grounds to give both rose plants. So I gave it a lot. Probably enough if it was a human to stay up for a week. The roses continue to flourish. Was it the coffee grounds or the weather?

I went and got another bag thinking my hydrangeas which are pink and should be blue. I figured that the coffee grounds were acidic and the hydrangeas needed more acidity in the soil to become blue. However, another friend told me to be careful and not to give the plant too much. So how much is enough?

I started to look for any university that did a study on coffee grounds. Mostly, I found articles written from gardeners or DIY’er reporting the same things I knew. No one seemed to answer how much. I ran across a question from someone in NJ asking about coffee grounds in the garden from Gardens Alive. Click on the link and read the entire article.

Gardens Alive had coffee grounds tested by Will Brinton, founder and Director of the Wood’s End Research Laboratory in Maine. He found the grounds to be very acidic, and some he felt were too acidic for even acidic loving plants. The article continues on his thought about adding them to your soil. And he certainly doesn’t think grounds should be used in their raw form. First, he explains, they are so acidic and so Nitrogen rich that you risk creating a ‘mold bloom’ where you spread them.”

Brinton favored using the coffee grounds for your compost. He recommended that you add a cup of lime or high quality hardwood ashes, which was preferred, to every ten pounds of coffee ground to neutralize their acidity in your compost pile.
As for composting,

“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 caused a damper for me. It seemed that I can only use the grounds for composting provided I add brown material such as leaves. To make matters worse, another gardening article I read called coffee grounds brown matter. Boy was I confused. So, I decided to dig a little deeper and called the Cooperative Extensions of Rutgers and Cornell to see if they agreed with Mr. Binker’s opinion. When I finally reached a Professor at Rutgers, he told me that he really did not have a lot of experience with coffee grounds and suggested I call the Rodale Institute. As for Cornell, an assistant at the Extension told me she would try to find me someone who could assist me.

Many of you may know the Rodale Institute through Organic Gardening, one of my favorite magazines. I thought it is worth a shot and called Dr. Paul Hepperly, the research and training manager at the Rodale Institute. He is well known as an authority in organic agriculture.

I told Dr. Hepperly what I had read on the internet and asked him his opinion if he thought coffee grounds were too acidic for the garden. His opinion was that once the coffee grounds started to decompose, their acidity was neutralized so that they are only adding nitrogen into the soil. His suggestion was to side dress the plant with no more than one inch at a time, and 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.

A couple of weeks later I received a surprising email for Adam Michaelides, the Compost Education Program Manager at the Cornell Cooperative Extension, asking if I had gotten my answers to my coffee dilemma. His advice was limited to coffee in compost because he did not have any experience with coffee grounds and soil.

“Coffee grounds are very acidic. So if someone (like a coffee shop) was composting mostly coffee grounds with some sort of bulking (brown) material, they might experience slower composting. This is because certain decomposers need certain pH ranges to live and if the pH is too low, some won’t be able to live there to break down the grounds. But, in general, backyard composters who have some coffee, and some leaves, and some other food scraps, and maybe some wood ash, etc. are going to be fine. When a diversity of materials are used, a diversity of decomposers will work to break them all down. As the material that is composting changes form, the pH will go way down, then way up, and then level off around neutral. Some composts are more acidic or alkaline than others, but some of this has to do with the way that they were composted, not necessarily the inputs.”

As for composting, I was still a little confused about what Dr. Hepperly meant about one part green to three parts brown. I asked what Mr. Michaelides’ opinion was about coffee grounds and composting. He replied,

“A more useful rule of thumb is 2 or 3 parts “brown” to 1 part “green.” This is by volume, so if you have one 5-gallon bucket of food scraps, you will need 2 or 3 buckets of dry leaves. As it applies to lasagna layering, one part brown will be on the bottom of a layer, the other on the sides and the third on the top. And you will have one layer of greens sandwiched in between. Hard to describe, but look at the diagram on that fact sheet.” See their online fact sheet.

The other day I dropped some green scraps in my compost to find a ton of small worms just lounging in the coffee, I never had this many worms before and I thank the coffee for my new visitors. So, I decided as I picked up another bag of coffee, that a little coffee will do my garden good.

For other uses of coffee grounds see DIY Maven’s post on Curbly.com:

Personally I like “the getting rid of cellulite” idea. If anyone tries this, let us know…

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Tagged as: coffee grounds, Gardening, Starbucks and free coffee grounds