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Eggshells and coffee grounds

May 24, 2012

Hello there, I generate a lot of both of these and so would like to combine them to use them as a stand-alone fertilizer (I give my other kitchen waste to a local pig owner). However, I haven't seen an exact "recipe".

Can anyone tell me how much powdered eggshell I should mix into my grounds to generate a PH neutral fertilizer?

Anything else I should beware of, in terms of balance?

Thanks so much

Comments (25)

  • Karchita

    Coffee grounds are nearly neutral ph, 6.9.

  • adriennepratt

    Thanks karchita, that's good but surprising news! I had read all over the place that they were most suitable for acid-loving plants?

  • Kimmsr

    Because the coffee you drink is acidic many people simply assume the grounds will also be. Some reports list the pH of coffee grounds as being 3.0 to 5.0 something without citing where that came from, while other sources, citing testing from various universities, as being in the 6.5 to 6.9 rnge which is slightly acidic but nearly neutral, 7.0.
    To know the answer to your question you would need to know what available nutrients your egg shells had.

  • toxcrusadr

    Second the info about coffee grounds. Most of the acid leaches out into your cup of coffee!

    Eggshells are high in Ca (stating the obvious I guess). I'm not sure if that's CaCO3 which would raise pH but that's the general consensus. Depending on how much of this mix you're using, it could alter not only pH but Ca levels. How's your Ca and Ca:Mg ratio now?

    Not surprised there are no recipes readily available. If this is a high volume thing, pounds per day, and you have access to an Extension or University soil lab, you could make several different mixes and have them test the pH.

  • adriennepratt

    Well that's very good news indeed. I guess I can forget about the eggshells then.

    We're not talking high volume, no, and I don't have a very large garden or anything. But should I be concerned about using only coffee grounds? As I say, all pig-edible kitchen waste is given away, plus I don't currently have any composting facilities. It seemed to me on the basis of what I read that the coffee grounds would be a net positive if I just added them to the watering can. Grateful to know if I'm not taking anything into account, though.


  • billums_ms_7b

    Coffee grounds, with the paper coffee filters included, are a wonderful addition all on their own.

    Instead of just leaving them on the surface of the soil, dig them in an inch or so. I tend to put mine near plants that are struggling and soon thereafter the earthworms just swarm that area.

    Worm poop is a great fertilizer, and the worms do a good job of aerating the soil and distributing the coffee grounds deeper.

    I just dug up some Japanese painted ferns that had received a lot of coffee grounds in years past and was amazed at just how many huge worms were still swarming about under those ferns.

  • luckygal

    I wouldn't forget about the eggshells as they are beneficial also. If you have slugs (and almost everyone does except me!) you can use crushed eggshells mulched around plants to deter them.

    I also wouldn't use the coffee grounds in a watering can but just lightly spread them on the surface of the soil (they also are said to deter slugs) or rake/hoe in between plants.

    How much is "a lot" of eggshells and UCG?

  • Kimmsr

    Every gardener should be concerned about adding only one thing to the soil they have. Does Ma Nature add only one thing to the soils she tends, or is it a variety of materials?
    Add many different types of vegetative waste to your soil as compost, or buried waste, or shredded leaves, or the waste plant material your garden generates. The greater the variety the more, different, nutrients you will be putting back.

  • jolj

    Coffee grounds are acidic here in S.C., but I get mine from the processing plant, so that may make a different.
    I will post the soil test on coffee waste if & when I find it again.
    It was enough to chance the color my Hydrangea: coffee grounds on one side & lime on the other of a 20 inch bush.
    By the way someone ask me about pine straw being acidic this week & I told them, when it is composted it is near, if not

  • Laurel Zito

    I find eggs to be a good thing. I compost them. But, I don't eat that many eggs. If you eat only a few eggs a week and they get distributed all around the garden. I don't think it will hurt, but if you had massive amounts of eggs shells, that would be an over load and not a good thing.

    I think the coffee will work if you dig it in a little bit at least. If you let it sit on top of the soil it will form a crust and attract flies. The crust will be white. If you mix the coffee with the egg shells and dig it in a little bit, this would be a positive thing. I don't know what kind of fertilizer you would get more it, but over all it will help your soil, provided you don't use massive amounts. The coffee will help the egg shells break down faster.

  • oliveoyl3

    Eggshells compost even faster if you dry & crush 1st.

    When I don't I see bits of eggshell even in the almost finished coarse compost from my bin.

    We keep a foil lined pan in the oven for the eggshells and when the oven preheats and as it cools off it's great for drying the shells. About once a week I empty the pan into an empty paper bag from sugar or flour to crush. I slip that bag into a plastic bag as double protection that I don't make a huge eggshell mess in the kitchen when crushing.

    Takes just a few minutes to do it & once a habit you don't even notice that extra step of putting the eggshells into the pan.

    When the bag is a little over 1/2 full I take it out to the garden shed or empty into the compost bin.

    I use the egg shell powder in tomato planting holes as well as mulch around cabbage family plants that love the calcium. I have acidic soil and heavy rains, so can't get too much calcium here.

    We raise chickens, so eat a lot of eggs. Sometimes, I give the crushed dried shells back to the same chickens in their feeder and it gives them more calcium, too.

  • pinks

    I take the same approach as corrine1--I dry my eggshells, pulverize them in an old coffee mill, then add the powder when I transplant tomato and pepper plants. I also mix a bit into the soil of those plants every few months. But I'm an amateur, so I have no idea if it really does any good or not.

    Slugs aren't that common on my balcony, but when they arrive they eat my sage. So I try to keep a ring of egg shells around that plant.

    Coffee grounds from starbucks and extra crushed egg shells go into my patio compost bin.

  • jolj

    There has been an on going debate on how long it takes to break down egg shells to be used by a plant. I say that it does not matter, the shells are not in the land fill.
    Someone posted to grind up shells & add a little vinegar to dissolve the shell, so the plant can use now.
    Do not remember who or where it was posted.

  • adriennepratt

    Hello everyone and thanks for the absolute wealth of information you have provided. I was about to say I'd just carry on as I have been doing, with the exception of digging in rather than adding to the watering can, as I had seen suggested elsewhere, but I just came across this article:



    "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

    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."


    Now I'm a little confused. What do we mean here by soil amendment rather than fertilizer? Okay, I see the grounds providing good aeration to my very dense volcanic soils (btw, I'm no longer in DC but in Ecuador!), but surely everything I have read until now suggests the grounds are a great fertilizer??

    Also, this suggestion to side dress is in marked contrast to all the advice regarding digging in.

    Total amateur here - your opinions appreciated!

  • Karchita

    I would disagree with just about everything Dr. Hepperly says.

    "He explained that once the coffee grounds are added to the soil, they start to decompose, and in turn, their acidity neutralizes."

    Yes, they will decompose in soil. No, their acidity will not neutralize because, as discussed upthread, they are nearly neutral to start. (There is also info on this in our FAQs, which I would highly recommend everyone take a look at.)

    "Ultimately, they are only adding nitrogen to the soil."

    No, they are adding a lot of things to the soil. For an excellent analysis see:


    "His suggestion was to side dress the plant with no more than one inch at a time."

    An inch is way too much. It will form a crust that water will not penetrate. The consensus around here seems to be less than a 1/4" for side dressing.

    "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."

    Ok, I also would not recommend piling more UCGs on top of old ones before they have broken down. That's just common sense. I apply once a year in the spring and the old ones are long gone. UCGs +are+ a mild organic fertilizer and it is not a good idea to apply any ferts late in the growing season, so I stop with all of them after mid summer, except for my winter veggies. As for what he means about soil amendment v. fertilizer, I have no idea. Coffee grounds are both. See the Sunset link for much better info than this guy's.

  • Karchita

    jolj, if you are talking about +unused+ coffee grounds then, yes, they are going to be acidic. The coffee brewing process removes the acidity and it ends up in the coffee cup. +Used+ coffee grounds have usually been found to be about 6.9.

  • jolj

    You are new so I will start with what coffee waste is.
    Whole green coffee beans,whole roasted coffee beans, unused ground coffee, Used ground coffee & Mostly coffee chaff.
    Everyone is reading papers, books & site on PHD's.
    I do not know what these people have tested or how, but coffee waste compost keep snails,slugs & weeds out of my garden very will. My Blue berries,raspberries,vegetables love it. I am at the point where I use straw,grass clipping & leaves as mulch on the compost. So I do not care what is in the coffee waste compost or it's pH, because I have had good growth from it's use.{{gwi:289776}}
    I am very please with this compost after using it for over 5 years.

  • Karchita

    Hi jolj,
    If you were talking to me, I have been a member here since 2004, so most people wouldn't consider me new, though I haven't been active a lot lately. I was responding to this comment that you made earlier:

    "Coffee grounds are acidic here in S.C., but I get mine from the processing plant, so that may make a different."

    Coffee grounds are acidic if they unused, as they may be if they are waste from a processing plant. Used coffee grounds are found to be pretty near to neutral consistently. And, by the way, all finished compost is also always neutral or nearly neutral pH; it's one of its defining traits.

    I agree with you that I don't really care too much about the particulars of my homemade compost. I get great results in my garden and that is all that matters.

    It sounds like you've got a great resource for organic material for your garden that is a balanced and rich mix of materials. Lucky you! I wish I had access to something like that.

    Happy composting!

  • toxcrusadr

    +1, I have compost envy!

  • jolj

    Sorry, maybe I should say new to me.
    It was not meant as a insult, I try not to repeat the same thing word for word in every thread. I think it makes me sound preachy & it must be boring to the persons who read every thread.See how I missed up with just assuming you where new, may have read your post some other forum, my mind is slipping now that I am 50 something.
    I know the coffee waste is acidic, because it has been tested & if I find the paper work I will post it. I believe what I read, when it sounds likely. I saw the test, so someone is wrong or they had a different test.
    No matter, like you, as long as my plants & the plants of friends who have gotten my compost do well, I am happy.

  • Karchita

    No insult taken and I have no doubt that your coffee waste could very well be acidic. I was just trying to make clear that coffee +waste+ is not the same stuff as +used coffee grounds+.

    Nice to meet you!

  • toxcrusadr

    Organic acids like those in roasted coffee will have a buffering effect, which means that more added will not change the pH by much. At the same time, a relatively small amount of acid added to distilled water (which is how solids are pH-tested, as you probably know) will show almost the same pH. What I've just described is *total acidity* which does not always directly parallel simple pH.

    So, if you were to titrate both a fresh brewed coffee and a sample of the used grounds extracted again with an equal amount of water, you might see 10 times as much acid in the brew, even though they both start out at an acidic pH.

    This may be what is going on with coffee. I haven't tried this experiment. If I was still in the lab, I'd do this stuff in a heartbeat just out of curiousity.

  • ma_guy

    If Dr. Paul Hepperly was quoted accurately then he is simply wrong.

    UCG are not acidic, end of story. If you like, use a ph test on a batch. I get 30 lb. bags of UCG from Starbucks and test regularly - always close to neutral.

    One thing I didn't see mentioned here is that too much UCG can create problems for plants not because of acidity but because of too much nitrogen. Put UCG around your tomatoes and you'll get lots of leaves, very few fruit due to the amount of nitrogen.

  • jolj

    Anything less then 7 on the pH scale is acidic.
    How do you defined acidic?

    Here is a link that might be useful: less then 7 on the pH scale is acidic.

  • toxcrusadr

    Yes, of course. OTOH the optimal range for vegetable gardening is 6 to 7 or thereabouts. So slightly acidic (pH 6) isn't going to be a problem. It's all a matter of degree.

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