Adding Egg Shells to Your Worm Bin

Someone recently asked whether or not it was ok to add egg shells to their vermicomposting systems. The question reminded me that this was something I’ve been meaning to write about for quite some time.

The answer to that question is definitely YES – egg shells are a great addition to your worm and compost bins. They are a great source of slow release calcium and can also act as a buffer, essentially helping to prevent excessively acidic conditions from developing.

I personally prefer to grind my egg shells up as much as possible before adding them – this helps to increase the rate at which the nutrients can be utilized, and also the rate at which the obvious egg shell fragments will disappear from your bin. I also prefer to leave the yolk residues in the shells rather than rinsing them out. This provides a bit of extra nitrogen (and other nutrients I’m sure), which never hurts.

I simply put my fresh shells in old empty egg cartons, making sure not to stack any of the wet ones on top of each other so that they can dry out quickly. Once I’ve amassed a serious collection of shells, I next dump them all in a plastic bucket and grind them with the bottom of a mason jar (any hard object should work fine). You can see in the pictures above what the shells end up looking like.

I’ve read that calcium plays an important role in earthworm reproduction, so you may also see a boost in breeding if you add shells to your bins. If you don’t eat eggs, there are some other options for adding calcium. A lot of worm farmers recommend the use of lime (calcium carbonate – CaCO3) in worm beds. If used in moderation, I agree this can be a useful material, but I recommend against adding it every time you think acidic conditions are developing (as a ‘quick fix’). You may end up throwing the balance of your system off kilter and harming your worms in the process. Composting worms are actually very tolerant of acidic conditions – apparently Red Worms in particular have a pH tolerance range of between 5 and 9, according to Dr. Clive Edwards (renowned vermicomposting researcher).

Rock dust may be a better choice than lime simply because it will likely be a little more slow release (like egg shells), and can contain other beneficial minerals as well.

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    • Alison
    • April 14, 2008

    Thanks Bentley, this is a great help ! I have been drifting the crushed shells over the lawn but I would like to include them in my worm bins.

  1. Great idea… crushing them. I’ve always just crumbled them by hand & tossed them into my veggie can. And they don’t get assimilated that well in the end. I’m going to try crushing them separately next time.

  2. What about some or all of the actual egg? At this time of year we always wind up with many more fresh eggs than we can use. I usually wind up scrambling a bunch of them and feeding them back to the chickens. I have been putting some of the egg shells in the worm bins and will probably try to be more consistent with it, especially if it can help reduce the acidity from too much citrus.


    • Bentley
    • April 15, 2008

    Hey Allen,
    As mentioned, I do leave SOME of the egg yolk in the shell, but if I had lots of extra eggs (that needed to be disposed of) I would likely create a separate composting system (maybe even a hot composting pile) since there is much greater potential for putrification and potentially nasty organisms developing. I definitely wouldn’t recommend adding them to any of your indoor worm bins or outdoor bins you work with a lot.

  3. Does it matter if the eggshells have been cooked or not? Can I put peeled hardboiled egg shells in there? How about hardboiled eggshells that have been dyed for Easter?

    • James
    • August 8, 2010

    I used to like to grind the shells after a day or 2 of drying in an old coffee grinder. Is this ok? My worry was making the shell fragments TOO small and sharp. Is there any chance of harming with worms if they were to ingest the shells after grinding? Would larger be better?

    • Bentley
    • August 10, 2010

    That’s an interesting question, James. I would be inclined to say “don’t worry about it”, but I really have no clue if this is the case or not. I would suggest spreading out the ground up shells really well to at least decrease the likelihood of this happening. I certainly didn’t see any evidence that the worms are being harmed by small fragments when I was grinding up my shells (I’m now lazier about it, opting to simply toss them in as-is for the most part)

  4. James,
    I pulverize the dried out egg shells and sprinkle them in,nothing bad has happened to my worms.
    The reason I pulverize the egg shells in a mini chopper is that the first time I used the Letty’s mini chopper, I ruined it and she got mad. So now I HAVE to use the mini chopper to justify ruining it.

    • Robert
    • August 17, 2010

    The difference between the two comments ” The answer to that
    question is definitely YES – egg shells are a great addition to your
    worm and compost bins. ” and the following question and answer.
    James’ Q. “Is there any chance of harming with worms if they were to
    ingest the shells after grinding? Would larger be better?”
    Bentley’s A. ” That’s an interesting question, James. I would be
    inclined to say “don’t worry about it”,
    ” but I really have no clue if this is the case or not.”
    I find it irisponsible to give advice if there is no proof that the
    answer is correct.
    I believe that it’s probably harmful to the worms to swallow sharp
    broken pieces of egg shells. I am going to locate some one with a
    microscope and see for myself what a ground up piece of egg shell
    looks like, compared to a grain of sand. In the mean time, I will
    reserve my ground up egg shells to spread around plants that I am
    trying to save from slugs.
    If you want to read the other side of this controversy, look up how
    others have written about slugs and how the egg shells deter them
    from going any where near egg shells.
    ” From Bonnie Willie’s site on slugs.
    7. Abrasive materials like ground egg shells, oyster shells or
    diatomaceous earth can be placed at the base of plants. As the
    slug ripples over the abrasive material their bodies become
    lacerated causing the slugs to die from dehydration.

    • Bentley
    • August 17, 2010

    Heya, Robert
    Mr. Irresponsible here
    Thanks for sharing your thoughts. I can assure you that my inclination to say “don’t worry about it” was based on the lack of evidence I have seen (absolutely NONE) that would indicate worms are being harmed during the 10 years I’ve been vermicomposting. It is also based on the numerous accounts of others who have been adding crushed egg shells to their bins. Aside from that, I was simply sharing a personal opinion (not even a recommendation, necessarily) – I always encourage people gather as much information/evidence as they can, and then to come up with their own informed decision.
    Discouraging slugs from attacking your plants and adding egg shells to your worm bed are two different things. When attempting the former, you would probably heap them up in a nice thick layer around the base of your plants, thus requiring the slug to actually cross over the material to reach the plant. When adding them to a worm bin, it’s a good idea – as I suggested above – to spread them out a fair bit (mix them in as well).
    Anyway, I value additional thoughts and discussion, even when people call me irresponsible (haha) and disagree with me – so thanks again for chiming in.

    • Robert
    • August 18, 2010

    Hi Bentley:
    Glad to hear from you. I wondered what got into me for firing off
    what I wrote. Thanks for taking it with LOL., and correcting my
    spelling of the word.
    I’m still interested to see the egg shells under a microscope.
    Have you ever had the opportunity to compare them to grains of
    sand under magnification?
    Thanks again for the response.

    • Bentley
    • August 18, 2010

    Hi Robert,
    Not a problem – no point taking these things too personally, especially when e-communication is involved! Your friendly follow-up certainly serves as an important reminder of this.
    Would be interesting to see how the shells look under the microscope, but have not had the opportunity to do so yet.

    • Roar Irgens
    • November 6, 2011

    I am just starting my worm box. I have previously ground egg shells in an old blendor and added that to my veggie garden. I plan to add it to the worm food. I do have a microscope. Will take a look.
    i have heard that the worms will nest in half egg shells. Any exoerience on that, anybody ?

    • Roar Irgens
    • November 6, 2011

    I find the comments usefull and interesting.

    • Chad
    • December 17, 2012

    We use raw aragonite in our worm bins. All it is is ground up mullusks shell.
    Calcium (CaCO3) 33%

    • Britton Cook
    • January 6, 2013

    Hi all! I started my worm bin august 2012 so I’m new at this but having fun doing it. I heard that adding egg shells was a good thing for the worms so i have saved every egg shell i have had for months (along with empty paper egg cartons), and have been crushing up the shells for them. Calcium aids the worms by helping them to reproduce, and also plays a role in aiding their digestion. While as important as calcium is, in order for any living thing to metabolize calcium, proper amounts of magnesium are needed as well. Which brings me to my question. I have heard of people using dolomitic lime to help in the magnesium area, but has anyone ever tried epsom salt with worms before? I ask only because epsom salt would be a great source of Magnesium without adding any more calcium to the mix. I feel like I have plenty of egg shells and don’t want things to get too far off balance. Thank you!

    • Adam
    • May 13, 2013

    I add a mixture of crushed egg shells, oyster shell flour and rock dust to all of my worm bins. I’ve had zero problems. They won’t swallow an entire chard of the shell. Even crushed, egg shells are still too big for that. And if you ground it up finely into a powder, they would still be fine. Just like when people add DE to their bins. The worms enjoy that too. I find it irresponsible to call someone as experienced as Bentley irresponsible for giving his opinion based on experience. If you don’t want to benefit from his info, fine. He’s helped me a great deal though and I’m not just a hobbyist in vermiculture.

    • Adam
    • May 13, 2013

    I cover my food waste with the above items at every feeding to keep the bins balanced

    • Cindy
    • May 21, 2013

    If you toss in large pieces of broken eggshells the worms won’t benefit from them as much as they will if you grind them into powder, which they can injest and use as grit. I recommend buying a cheap $17-$20 coffee grinder. I use an old Krups grinder, which, by the way, also does an excellent job of grinding spices. It allows me to grind them into a fine sand like consistency, or powder, depending on the length of time I grind. I save eggshells until I have 2-4 dozen or more, then I spread them out onto a sheet of foil and toss them in the oven and bake them at 350 degrees for 30-60 minutes, then let them cool before grinding. The primary reason I bake them is to remove moisture from the shells to make it easier to grind them and keep them from clumping. Baking also kills salmonella, if present, which isn’t harmful to the worms and they can process and eliminate, but could ptentially make me sick.

    II store my powdered eggshells in cheap plastic commercial sized salt & pepper shakers that I picked up at a discount dollar store. I sprinkle eggshell powder and mix it in whenever i make up fresh bedding and I make a habit of dusting the bins every 7-10 days, and I sprinkle a little bit on any food when I add it. This has not only managed to help keep my the pH i my bins balanced for 2 1/2 years, but it also help rovide then with a steady supply of the grit they need.

    Regarding adding whole eggs….. I tried this on several occasions. I added two 1/4″ thick slices of hard boiled egg to one of my bins and the worms devoured the whites, but wouldn’t touch the yolks. In ‘Worms Eat My Garbage’ Mary Applegate said it’s safe to add an egg occasionally. Knowing what I now know, I would limit feeding to an occasional eggwhite, but never any yolks. Eggwhites are very high in calcium and low in fat, and the calcium may very well be what my worms were attracted to. Yolks, on the otherhand, are high in protein and fat, so if there is any correlation, the protein might cause protein poisoning (a.k.a. the dreaded and often fatal, string of pearls, or sour bin syndrome). If you would like to try feeding your worms eggwhites, recommend you start off by adding only 1 or 2 thin slices of boiled eggwhite and that you check your bin after 24 hours and if your worms haven’t been eating them, toss them out. In any event, whether the worms are eating or not eating the eggs, you should remove all remaining egg within 48-72 hours before it begins to putrify and start creating a stench.

    • Adam
    • May 22, 2013

    Cindy… Yeah if you powder the shells, that is good because they consume it much faster. They will still consume larger pieces though. I’ve noticed that crushed shells do last much longer than the fine oyster shell flour. The rock dust usually gets devoured as well. The crushed shells do disappear after awhile though. Regarding larger pieces not benefitting as much, I somewhat disagree. They don’t get consumed as quickly as powder does, but they offer other benefits. One thing I’ve noticed about halves of egg shells is that they love laying cocoons in them. I’m not sure the exact reason for that (protection, membrane, etc..). Any way you do it (coffee grinder, food processor, crushing by hand, leaving whole will help the worms tremendously. One thing I will say is if you are trying to use then to keep the PH neutral, the smaller pieces are better because they’re easier to disperse. If you don’t eat enough eggs or have a restaurant giving their shells to you as I do, rock dust or oyster shell flour alone should be sufficient.

    • Melissa
    • May 26, 2013

    Hi all,

    Helpful comments, thank you. I realize I haven’t been crushing the shells finely enough, so they never get assimilated. One question, how are folks storing the empty egg shells before grinding? In the fridge? The freezer? Thank you!

    • Adam
    • May 28, 2013

    Hello Melissa,

    What I do is rinse and thoroughly air dry my egg shells. I like to use as little energy as possible because that defeats the purpose of going “green” IMO. After that, you can store them wherever. I have a large 55 gallon drum in my garage that I keep them in. I don’t keep any yolks on them because that can get pretty smelly as Bentley stated.

    • Melissa
    • May 28, 2013

    Thanks, Adam.

    • Teresa
    • March 10, 2014

    We just started our first bin. We are a large family who eats up to 5 dozen eggs in a week sometimes. How much egg shell is too much? Thanks.

    • J.L. Lucas
    • March 12, 2014

    a second hand coffee grinder works well to crush the egg shells

    • Adam
    • March 13, 2014

    I used to use a food processor to grind up egg shells. Even using that did not create powder unfortunately. I now use a Vitamix blender. That thing makes a very nice powder. This works very well and let’s the eggs cover things much better than the small chards in order to keep the PH neutral. This also makes it so your castings don’t have un-processed egg shells at the end (even though that isn’t really a big deal). I still also use my special grit mixture.

    • Adam
    • March 14, 2014

    Teresa…I don’t think there really is a “too much” when it comes to egg shells. Obviously you don’t want to “drown” them in the shell powder or over run a bin with whole egg shells. I usually just lightly coat my fresh bedding with my egg shell flour and sprinkle a light layer over any food that I add to the bins. That stuff is valuable to me so I don’t use too much.

    • Teresa
    • March 16, 2014

    Thanks. I may be overdoing it a little. The worms seems to like it, though. I sprinkle it on top and it’s worked in within a few hours. We’ve been using a molcajete to crush our shells. It’s like an oversized mortar and pestle. It’s not powder, persay, but it’s small enough to suit me and the worms. I’m not particular with the end product since it will just go on my outside plants here at home.

    • HarryCK
    • July 20, 2014

    No one has answered the question above about using epsom salt in your worm farm. Epsom salt is supposedly very good for your plants, so I too would be interested in knowing whether you can use it with worms or not.

    • Bentley
    • July 22, 2014

    I would avoid using ANY type of salts, Harry, since worms are VERY sensitive to them. I might add some epsom salts at the base of my tomato plants (even though plenty of worms in close proximity), but only because there is plenty of safe habitat close by.

    • Britton
    • July 25, 2014

    @ HarryCK: I have used epsom salt in my worm bin. first dissolved it into warm water, added cool water, and then poured it into the bin. Epsom Salt isnt “salt” (sodium chloride) so it won’t hurt them at all. I couldn’t tell if it was benefiting them so I don’t really do it anymore. But it certainly didn’t hurt them.

    • Bentley
    • August 2, 2014

    Britton – there are many kinds of salts, and sodium chloride definitely isn’t the only one that will harm worms. That being said, there likely ARE quite a few salts that won’t be harmful.
    Very interesting re: epsom salts – thanks for sharing that!!

    • Martin
    • April 21, 2015

    I have Interesting observation to share. I use ground egg shells regurarly and worms always seem to be doing great, they never try to escape. I don’t believe it can hurt them although I was also worried in my beginnings. I just purchased very powerfull hi-end blender recently (cca 600 eur) for smoothies but also for the worms. After I’m done with the smoothie, I blend the peels and other vegetable leftovers and incorporate it into the compost (plastic indoor stacked bins). Just to speed up everything. Now I also blended the egg shells into powder (broke at least 2 food low cost food processors in past on eggshels) and this time it was super fast and super smooth powder. After I added the worm smoothie and mixed it with the compost I sprinkled a lot of eggshell powder on top to neutralize the acidity (probably should have mixed it in as well). Very soon mass of worms covered the surface (they are stored in the dark) and they seemed to enjoy it a lot. They didn’t try to escape – not a single one was crawling up the wall, and they started hiding as soon as I lit up. Now I don’t know if it was because of the acidity of the worm smoothie (mostly potato peels, no citruses) or the love for the egg shells but it was certainly very interesting and new phenomenon 🙂

    • Martin
    • April 21, 2015

    I don’t rinse or heat the eggshells. I only let them dry out in a cardboard box or paper bag on my balcony and I grind them if they are about one week left to dry and I never had any issues with salmonela or anything yet

    • Janine
    • June 11, 2015

    Hi I am new to this do I add the crushed egg shell to the food area or the home area. Thankyou

    • Kris BL
    • July 24, 2015

    Nice Thread ~ Enjoyed reading about everybody’s experiences.
    I only began my bins a few months ago after discovering thousands of African NightCrawlers living in my clogged roof-gutters. The eggshell Q’s were quite informative.
    Re: EpsonSalts for magnesium > a long time farmer told me that 10g/1Litre water is enough to benefit but not hurt them.
    ~ i’ll start with that soon & if i notice any changes i’ll post an update…

    • jW
    • August 18, 2015

    Can I put raw egg in the worm bin? I always have a few cracked eggs and I wonder if I could put RAW egg in the worm bin Or if i could put raw egg in my regular hot heap compost container? What do you suggest? What would you do with raw eggs?
    My egg cartons always has an egg or two that has cracked inside of it. Should I wash the egg carton out or let it dry before putting it in the worm bin Or before putting it in the regular compost? Thank you!

    • Bill
    • August 8, 2018

    Thanks for the resource!

    Any tips on how to sift out the eggshells if you have been doing it wrong and just throwing them in? I picked up a free bin off Craigslist but the lady didn’t really take care of it very well – riddled with cockroaches, springstails and drenched the first time I picked it up.

    Anyway its been 2 months and things are looking better, finally managed to dry it out and the worms seem happy (breeding and feeding)

    I can finally see the resemblance of the black gold but it’s also riddled with pieces of sharp egg shell. Everytime I turn it, I can feel 1000 worms cry out in pain and confusion – always finding a few cut up ones squirming.

    Any suggestions on how to take out the egg shells so I can crush or dissolve in vinegar?

    Thanks in advance for your time and ideas!

    • Frank
    • December 22, 2020

    I always put my eggshells in a coffee bean grinder, and reduce them to a fine powder. Worms must like it this way as it completely disappears from sight after a week or so. Frank

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