This summer I kept more than 1,000 lbs. of “garbage” from getting hauled dozens of miles away in a 3 mpg vehicle to an incinerator. I also saved money and got great compost.
Spurred by a question from JP Greenhouse, I decided to see how quickly I could make ‘urban compost’ with nothing but coffee grinds and newspaper.
For about eight weeks:
- 80-120 lbs. of coffee grinds/week, and
- almost every newspaper we got,
went into a town-discounted ‘New Age Composter’ compost unit. The compost turned out great, with near-perfect pH (6.9), nitrogen within norms, and very high potassium. If you don’t care about the details, you can skip to the test results below.
More details:
Trash bag with 30 lbs. of coffee grinds
Coffee grinds are easy and plentiful. The local Starbucks, instead of giving me the little bags of used coffee grinds, would give me a trash bag-full at a time. In return I’d bring them various items from the garden.
Each bag was 20-30 lbs. and I retrieved several per week, sometimes two per day.
Some of you, like I did initially, might be saying “Your compost will be too acidic!” Turns out, as studies have shown, the acid gets washed off during the brewing process, so your coffee may be acidic but the grinds aren’t.
Shredded newspaper. Image courtesy of David Bleasdale, some rights reserved.
Compost needs both nitrogen (which the coffee grinds supply) and carbon. Carbon typically comes from adding leaves but I didn’t have any in the middle of the summer.
Our house is, however, one of the last faithful subscribers to several newspapers, which, as a tree product, is high in carbon. (Just make sure you’re using newsprint, not the inserts or magazines. Also, a friend who is an editor of a “wicked local” paper says they don’t always use soy inks, so check your source.) We used mostly the New York Times, Boston Globe and Wall Street Journal.
Update: Newspaper is as safe to use in the compost as any carbon-rich source. See this post.
I used a shredder to rip the newspaper into small pieces so they would compost faster. (One of my original concerns was the time it would take for that much coffee grinds to decompose – smaller items decompose faster.) There were some days I’d spend an hour shredding newspaper with my son in a shredder that would only do a few pages at a time.
In addition, food scraps from feeding a vegetarian family of three went into the compost, but that didn’t amount to much volume compared to the other items.
All of this went into a “New Age Composter” BIN-24 compost unit I got for $40 from my
This is the type of composter used, available from the town for $40.
town (Arlington, MA) DPW. It is subsidized through the MA DEP. I like the unit, which can be set to a number of sizes – I had it at its largest – almost a full cubic yard.
For most of the approximately eight weeks, the compost had been cooking very well, hovering between 120-140 degrees farenheit. I turned it at least two-three times each week to allow air in. Several times I had to add water because the pile was so hot it became dry.
The UMass Soil lab analyzed a sample of the compost and here’s the good news:
- pH was 6.9 (the goal is to be at 7.0)
- Nitrogen was high, as expected, but not out of the norms.
- Potassium was very high – I didn’t know until after receiving the test that coffee has lots of potassium.
- Phosphorus was between high-very high.
- Soluble salts were right where they should be at 1.79 ds/M (It should be less than 2 for multiple use options.)
The other news:
- All compost is typically short on calcium, and mine was no exception. So despite adding at least two eggs/day to the compost, calcium levels were still low-to-medium (7345 ppm).
- The “Coarse Fragments” were 56.4% – less than 20% is preferred. This was due to not-completely composted newspaper bits. After the compost had already started to cool down I added more newspaper, which never did decompose.
- At one point it did start to stink. This was because at the start I wasn’t adding enough carbon or newspaper at the start of the experiment.
- Lead showed up at 2.2 mg/kg, or 2.2 ppm. This freaked me out until I learned that background concentrations of lead show up an average of 10 ppm. (Update 4/28/2018 – UMass now says background concentrations average 15-40 ppm.)
- The finished Carbon to Nitrogen ratio was 11.7:1 – it should be around 15 or 20:1. Likely, because I didn’t add enough newspaper at the start of the experiment, there was insufficient carbon in the compost. Note that this is different from total nitrogen, above, which was within the normal range.
Conclusions:
I got almost a cubic yard worth of good quality compost for free, and I got it fast. I also kept a LOT of garbage from the waste stream, as well as paper from having to be transported to a recycling facility. It was a great way to get compost quickly, free, while reducing emissions from transporting “garbage.”
Please remember, be kind to the coffee shop that supplies your grinds!
*Thank you Robin V. for help with some of the science!
UPDATE: 1/25/2015
Here are some references that document used coffee grounds are not acidic:
Oregon State University Extension
Sunset test of Starbucks coffee
what about using coffee grounds that have not been brewed, straight from the can they came from? also, what about using coffee, along with the grounds that they were brewed from? would the ph be more acidic? i am growing strawberries, which love acid. thanks in advance.
The answer is along the lines of “everything in moderation.” Fresh coffee grounds still have the acid in them, so if you drop those into the compost they may increase the acidity (lower the pH) of the compost. However, the reality of that is going to depend on how large your compost is and how many fresh coffee grounds you’re adding. If you add a 5 lb bag of fresh coffee to a 5 gallon bucket of compost, it will affect pH. If you add it to a cubic yard sized container of compost, it isn’t likely to make much difference.
Same for using brewed coffee – a little bit is fine, but if you’re dumping gallons of coffee from the local cafe, that will be different.
As far as growing strawberries, they like a soil that is only very slightly acidic. According to Nourse Farm (an excellent vendor of berry plants and more), the optimum pH is 6.5–6.8. Neutral pH is 7. Best bet is to test your soil to find its current pH and work from there. Good luck and enjoy!
Just wanted to know your thought of compost pile on top of soil and added paper coffee grounds etc to top and keep it turned.
That’s fine. Keeping it all in a container, preferably with hardware cloth on the bottom to keep out intruders, is usually a good idea.
“Studies have found those three herbicides survive the compost process and will kill of various garden favorites”
We surmise that it was compost that the vegetable-killing studiers applied,
but the statement does not say that.
Regardless, thanks for informing us about those herbicides.
I think my statement makes it pretty clear that it is the herbicides that survived within the compost that caused the problem but if not, I apologize and thank you for making it clearer.
Do not use oak leaves in composting. They are alliopathic and will kill or retard gardens
That is not at all accurate and is not supported by science. Oak leaves are high in lignin and may be slow to break down but they are most definitely NOT allelopathic.
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Jeremy 1st of all what a great read, very informative. Could I use a plastic Rubbermaid trash can as my composted? I already have picked up bags of Starbucks coffee grounds which I used in my vegetable and flower garden all summer. I liked the idea in one of the comments about using a shredder to shred the newspaper. I would normally have used shredded office paper so was glad I read your response to using shredded office paper. Once again thank you so much for your time and efforts in the article and responding back to us all. I am sure we can all admit that we have all benefited from this article!
Thanks Jennene, I appreciate the kind words.
I imagine the rubbermaid trash can work , but it may not last as long as some other options available, and it will (typically-sized units) only hold around 30 or so gallons of material, so it may fill up very fast. I also wonder whether it is strong enough to handle all of that material as you attempt to turn it. So I guess I’d say that if you have the ability to get a larger, stronger unit, you might want to take advantage of that. In MA, many municipalities sell the New Age Composter, of which I am a big fan.
Regarding the newspaper (and I should probably link to this in the piece above), I was moved to do some significant research on the safety of newspaper in compost, and wrote about it here. It is long, but the spoiler is at the top, if you’re short on time.
Thanks Jeremy,
I appreciate all the info, if I may, I was just curious if maple leaves & chopped up corn stalk’s be to much nitrogen mixed in with my coffee grounds & news papers?
a novice at composting…thanking you again….
To be clear, what I did was a fun experiment, but you should use food scraps in addition to used coffee grounds, if possible.
Leaves are great, even better if chopped with a leaf shredder or lawn mower. Corn stalks are more difficult to break down, but certainly usable. These and newspapers are carbon-rich materials. Foods scraps and used coffee grounds are nitrogen rich. For every container of nitrogen-rich material, add two or three containers of carbon-rich material. Good luck!
Jeremy,
Attempting composting……
I have never made any “home made compost”…..a few questions if I may.
Can a 50 gallon steel drum be used for making compost & could recycled office paper be used in place of new papers with coffee grounds? at years end I always throw the leave in the garden, should I throw them in the com-poster instead?
Thanks,
Good questions.
A steel drum should be okay, if perhaps too small*, until it rusts, as long as it hasn’t had unsafe material inside. However, I think that preparing that drum for use might be more work than it is worth. You’d want to poke holes around the side for air, perhaps remove the bottom so soil bacteria have easy access, and to keep it from tipping you’d probably want to sink it in the ground several inches, unless you plan to cap it and roll it along the ground. None of that is necessary, of course, but those would be commonly accepted “best practices.” There’s a decent chance you can buy a compost unit (or salvage other materials) for little money and/or less work.
As for the office paper, I don’t recommend using it. The paper itself likely has some amount of dioxin in it and unless you can source the inks, there’s a decent chance they have chemicals in them that you don’t want in your garden. The safety of composting office paper is a common discussion in composting circles, and I stand by my commonly-held position, as it is backed by science. Put the office paper in the recycling bin, put shredded newspaper in the compost.
Good luck!
* – A cubic yard is a standard size for compost units. There are 200 gallons in a cubic yard.
Not only is this a great idea for individuals but also businesses. Most offices have an abundance of coffee grounds and shredded paper. Our company, Whitaker Brothers has recently started its own composting experiment using nothing but coffee grounds and shredded paper (www.shredgarden.com). We’re looking forward to seeing the results come springtime, but based on your results it looks like we’re on the right track.
thank you very much for this helpful article – will the filters that i use in my coffee pot be a problem? i used to just toss them into my pile – but for this particular experiment would they affect the balance? thanks!
Coffee filters are fine to add to the compost – they are carbon-rich material, just like leaves or newspaper. Let us know how it goes!
Hello this great info as I now have unlimited access to coffee grounds & chopped leaves & have been adding them 50/50 to my compost been & it’s heating up fast.
I always like reading about a scientific study & I experiment on my own to some degree
You said most compost is lacking calcium so what can be added to it or the soil when using it?
I do add egg shells but I think they take years to break down.
Thanks for sharing your experiment
My wife makes coffee just about every morning in a reusable filter. She gets the coffee from the farmer’s market where she works. I am pretty sure that it is organic. I am not a coffee drinker so I don’t read the label. Each morning I clean out the filter after she goes to work. After doing this for awhile, I started feeling guilty about throwing it in the garbage. We have two pots on our deck that contain Dahlias. They were dormant during the winter months, so I forgot what was in them. I chose to dump the daily grounds in one of the pots, but for some reason not the other. It became an accidental experiment. Now I don’t know what the difference was in the soil before the grounds were added, but the dahlias have been growing for the past couple of months. The pot with the grounds in it is very much more healthy looking than the other pot. I did not even dig them into the soil. I just dumped them on top and kind of smoothed them out just to make them look more tidy.
I live in the Arizona desert and wonder what combination of coffee grounds, etc. would be best. Lots of calcium in our soil here!
Judy, the combination to make compost is always the same (approx. 1 part nitrogen to 3 parts carbon) no matter where you live. That is the recipe for compost. You can, of course, change the ingredients so they include more calcium (eg-egg shells) or less calcium (eg-most vegetable matter) so that the end product contains varying amounts of different nutrients, but I wouldn’t worry about it too much. Good compost is good compost, no matter where you live.
Just curious about the pesticides used on coffee beans. I know that starbucks has one or two organic brews but the majority of their gounds would be from heavily sprayed beans. Still a great article, and thanks for sharing!
Hi Jody. There’s little doubt in my mind that herbicides were used on the coffee beans. Studies have shown that most pesticides will degrade with composting. This is NOT true for the pesticides picloram, clopyralid or aminopyralid. Studies have found those three herbicides survive the compost process and will kill of various garden favorites like tomatoes, potatoes, cucumbers, peas and more.
My understanding of those three herbicides is that they would not be used in a coffee plantation situation, but rather in cattle grazing areas, so I feel safe using the coffee grounds making compost.
Thanks!
Really informative, thank you. Love having real data, and some surprising results.
By no means do I want to discourage your efforts, but I did have to wonder how multiple trips to Starbucks each week were any better than hauling trash or buying one cubic yard of compost from a reliable source.. Sure I get the overall goal of composting and we have a worm bin, but unless the source of your materials is already on hand or within your existing travel routes, I don’t see a reduction in the carbon footprint. Perhaps your Starbucks was located in the same mall as your groceries or other planned destinations.
I typically went to that Starbucks each morning, and it is within walking distance of several stores I frequent. I’m not suggesting everybody make daily trips to their local coffee shop for large bags of used coffee grounds, but if a lot of people do it every few days, then we’re working together to reduce the load.
If a garbage truck can now make X additional pickups before driving 30 miles to the incinerator, isn’t that a good thing? I would be surprised to learn that wet coffee grounds somehow ignite and burn in the incinerator faster than other wet items. This Starbucks very close to my home (though at the bottom of a hill – I’m not about to hike 30 lbs. of coffee grounds uphill daily.)
Finally, there is no “reliable source” of compost in my area that I am aware of, and it isn’t for lack of looking. They all make use of yard waste which may or may not contain various pesticides, including from the pyralid family of herbicides, which are known to kill various vegetables even after going through the compost process.
I use shredded paper and coffee grounds in my vermicomposting. The combination works fine with the red wigglers also. The bacteria that the worms eat seems to flourish on the coffee grounds.
Vermicomposting is a good option for those that do not have the room for composting bins.
Thanks Jeremy. Some great information there.
I have recently been given access to fresh coffee grounds from a very busy machine at a garage where my partner works, and as I like to walk up there to pick her up after her shift, I am bringing home a few pounds of free compost gold most days of the week. 🙂 It will all go to the allotment where it will live its ‘second life’ nurturing plants half a world away from where it was produced.
That’s great, and while there’s not much we can do to reduce the carbon footprint of growing/shipping the coffee, at least we can reduce the carbon footprint on the tail end. Enjoy!
Jeremy, thanks for such an interesting, informative article and so good to see an analysis of the end product. That’s proof of success! You’ve restored my faith in coffee grounds!
Just a comment on shredding news-paper: if you’re lucky enough to have a garden mulcher that can chip branches (ours does up to 65 mm diameter) you can produce a beautiful fluffy pile of moist shredded news-paper. The trick is to soak the news-papers, ,roll them up like a tight Swiss-roll, then feed these rolls into the branch chipper section of the machine. My wife also loves this stuff to use in her worm farms.
Happy composting and thanks for such good info.
Jeremy,
This was a pleasure to read. Very well done and incredibly informative. I didn’t know that about the acidity washing off of the grounds during the brewing process. So what do you think about the calcium deficit, did you do anything to address it? Add some calcium carbonate, maybe? My property is on a bed of limestone so adding calcium is not my issue, magnesium is (I want that 7:1 ratio – Ca:Mg). Nonetheless, there are several rock dusts on the market that do a great job of adding calcium to composts along with a wide array of other trace minerals.
Again, thanks for the great read.
Thanks Dave, I appreciate the kind words.
Like I said in the post, compost typically lacks calcium. I think that’s a good lesson for all of us that even if we add lots of compost to our gardens, calcium may not be replenished at the levels we want. I prefer to avoid lime for a number of reasons, perhaps most importantly that if the pH of the compost is excellent, I don’t want to mess it up by adding lime. Instead I use bone meal, and I’d use it after mixing the compost with the soil first (or simultaneously) – not adding it to the compost.
Thanks again!
Jeremy
An hour at a time shredding paper… How many hours did you spend total in paper-shredding?
I’m a huge advocate of cold composting, I simply don’t have the time to spend hurrying a natural process.
Some people use that paper in their concrete mixes…
Appreciated the article… I’ve noticed that dumping grounds out on the ground didn’t create lush growth, interesting to hear an explanation for that.
Stone, I spent more time than any rational person would want to shredding paper, but it was as an experiment. Even in urban areas where people might not have access to shredded leaves, or anywhere that someone might have forgotten to collect leaves in the fall, it is still possible to get good quality compost with readily available free items. (I should also note that my shredder doesn’t like more than 4 sheets of paper at a time, which contributed to the time spent shredding.)
For me, I still prefer using shredded leaves when possible. However, if I run out of leaves (as often happens in spring and summer, before leaves have fallen) then I know I’ve got a readily available source of carbon to help the compost along and keep the stink down.
Thanks!
Jeremy
I’ve read that ALL finished compost is pH 7.0, regardless of what goes into it. 6.9 being pretty darned close to that. Though your point about coffee grinds losing their acidity once used still stands. However, it may be the composting process and not the loss of acidity in the grinds that caused the near-perfect pH (maybe the compost was a touch under-done?). Great work, nonetheless! We are losing great stuff to the trash landfills and incinerators that could be used to nourish soil.
Thanks Deborah. I’ve also heard that finished compost goes pH neutral almost regardless what is added, and it may be true. However, I used a pH meter on a few of the big bags of coffee grounds and it always registered somewhere around 6.9. I’ve now read several studies saying that the acid from coffee is washed away in the brewing process and into our cup o’ joe. The end product (used coffee grounds) are now pH neutral and great for gardeners.
Thanks again!
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Excellent post and experiment Jeremy. Just goes to show, you don’t need to get fancy with making compost. But I must say, I was surprised and pleased to know that even with only two ingredients, you were able to make such a well balanced result. Thanks for posting your experiment. Well done!
Excellent breakdown of your breakdown, chemically speaking. Delighted to learn more about your efforts; thanks for sharing.