Egg Shells

mr_yanNovember 9, 2011

How does everyone handle egg shells for bins? How far do shells need to be pulverized to get incorporated?

Dried and crushed

mortar and pestle

food processor / blender

toss the broken shells into the bin


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I have tried just throwing my shells in, and they never seem to decompose. So I admit I go to a lot of trouble. I save them up in the freezer until I have oodles and oodles. Then a couple of times a year, I throw them in the oven on a cookie sheet lined with waxed paper to sterilize them and get them really brittle. After they cool off, I run them through an old coffee grinder I use to grind spices. This makes them into a very fine grit. A lot of trouble, but it works really great and once they're in the bins, I never seem to see them again, and the worms are happy!

    Bookmark   November 9, 2011 at 10:49PM
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I actually use a mortar and pestle and grind them while watching TV :). I aquired one I think as some gift, one of those things for a kitchen table to make it look rustic I guess heh. It reduces them pretty quickly into small pieces, then I mix them in with big feeds so if things do get nasty in the middle at least it won't go acidic.

    Bookmark   November 11, 2011 at 12:38AM
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I bought a blender from Craigslist for $10

    Bookmark   November 11, 2011 at 1:35PM
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Although worms seem to love cuddling up inside their smooth curves I have a second compost bucket in my kitchen. The first being for all plant material the second being only for egg shells although clam shells too would fit in this catagory. I smash them down when more need to fit in. Then when company is coming and I want to clean up the counter a bit, I pour them into a paper bag and roll over them with a wine bottle. Shake, roll, repeat. Then I just toss them in bag and all.

    Bookmark   November 12, 2011 at 9:54AM
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I take the egg shells and rinse them well and then put them in the basement to dry out.

Then when I go to feed the worms I put the egg shells in a bag and roll a softball on the shells to crush them up then sprinkle them over the bin.

    Bookmark   November 23, 2011 at 11:33AM
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There is no wrong way to do this folks. Everybody does it. All methods are ways make the calcium bio available. Some ways are just quicker about it. So how about it. Are your egg shells doing the Bachata, a belly dance or Cha Chaing into the bin? I'm ready to hold up my 10 Vote!

    Bookmark   November 23, 2011 at 11:51PM
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Like equinoxequinox comments, I have toyed with several ways to incorporate egg shells to the compost bins and blending along with kitchen scraps works best for me. I was curious as to why Worms4Tracy felt the egg shells needed to be sterilized. As Worms4Tracy mentions the pulverized egg shells seem to last for a considerable time before breaking down, or dissolving, or whatever they do. Unlike coffee grounds which have no food value but are readily devoured by worms, I don't think worms actually feed on these pulverized egg shell. Wouldn't mind hearing your opinions on this subject.

    Bookmark   December 19, 2011 at 9:39AM
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I let the shells dry out for a week or so, then grind them up in my coffee grinder. If any shell remnants are left in the grinder, they just end up in the next batch of ground coffee beans...

Here is a link that might be useful: Why do some people put egg shell in coffee grounds?

    Bookmark   December 19, 2011 at 1:03PM
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So morgan_3 sheds the light that egg shells don't really get consumed. That makes sense though. The shells would have to be nearly powder to be ingested buy a worm.

Would I be better off just crushing the shells and tossing them in the hole when I plant my tomatoes? I have been having trouble with BER and already have been diverting the shells from the bins to another bucket.

    Bookmark   December 19, 2011 at 7:35PM
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What is BER?

I include well crushed egg shells in the worm bin because I think they temper acid. They should have microscopic pits and roughness that provides surface area for tiny flora and fauna in the bin.

    Bookmark   December 19, 2011 at 9:03PM
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mr_yan: what is BER?
What I have learned so far, egg shell is supposed to neutralize the bin if it is too acidic. Pulverized eggshells is supposed to act as grit and help the worms digestion system, same reason why it's sometimes mentioned to add a bit of fine sand when you start a bin. My logic says that in both cases it will serve a better purpose when ground rather than big chunks. Just like gardening, this is not a must that you have to follow to the letter. You just do what you feel like doing.
Having said that, I do like to know the reason why somebody does/doesn't do a certain way and I can apply that to my situation.

    Bookmark   December 19, 2011 at 9:10PM
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BER is blossom end rot on tomatoes and, to a lesser extent, cucumbits like melons. It happens when the plant is not getting enough calcium to build healthy cell walls. With weak cell walls the blossom end of the fruit, where it is growing fastest, starts to collapse and turn a rotten brown colour.

If the shells are not of much value to the bin, other than pH control, adding crushed shells right to my garden may be of more use to me.

    Bookmark   December 19, 2011 at 10:09PM
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Cudo's otis, I was wondering if anyone would comment on the egg shells acting as a grit in the worms digestive system, much like birds eating gravel. Water blending, I find does a great job in not only pulverizing food, but egg shells as well. I offer coffee grounds directly to the trenches when feeding the blended point in blending the coffee grounds. Coffee grounds and egg shells in the spent media are excellent additions to your spent media when used in garden projects even if the worms are not getting food value from either one, they still have other benefits to the worms.

    Bookmark   December 21, 2011 at 6:43AM
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emily_ak(z2 AK)

I've read that worms need calcium to help produce their egg cases. And the calcium carbonate in egg shells is a good buffer, and will help to stabilize the pH in your worm bin. Fruit flies and fungus gnats in particular seem to like acidic conditions, so adding some ground egg shells will help to minimize these pests. My household uses a fair amount of eggs (1.5 dozen per week on average). I save about 1/3 for the worms, 1/3 for the outdoor compost bin, and 1/3 for use when transplanting tomatoes and peppers.

Emily in snowy AK

    Bookmark   December 23, 2011 at 4:27PM
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mr_yan: thank you for explaining BER. My neighbour gave me 4 tomato plants and 1 of them had BER. At the time I thought it was caused by too much rain we have been getting. Now I know better.
I don't understand why some people wash the egg shells. IMO, whatever eggwhite is left on the shells will make a welcome food source for worms.

    Bookmark   December 23, 2011 at 5:37PM
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Sounds like I will add some shells to my bin. Probably go with the 1/3 1/3 1/3 route that emily_ak mentioned.

I don't think I will wash the egg shells prior to grinding them but I will bake them (hmm roasting a chicken and some egg shells at the same time). My thinking is I will grind them in my coffee grinder. Currently I don't use the grinder as I get coffee at work but I do want to be able to use it for coffee again.

    Bookmark   December 23, 2011 at 9:22PM
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"How far do shells need to be pulverized to get incorporated?" I do not think it matters soil science wise, only if you do not want to see the shells.

Please what ever way you crush, pulverize, blend, grind your shells moisten them so you are not breathing the dust.

I am not on the "add egg shells to the vermicompost bin because worms need grit for their digestion" bandwagon. It is a great story, but sorry, I am not on that road.

Egg shells are good because they need to be incorporated into a good use. They help with surface area and magic electrical things happening in the soil.

However far they are broken down, nature will finish the job. Maybe in a million years.

"in the oven on a cookie sheet lined with waxed paper to sterilize them" Please purchase a large fire extinguisher.

What ever way you do it, crusing shells for the bin is great fun!

    Bookmark   December 24, 2011 at 2:49AM
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Just wanted to put my 0.02 USD,

Calcium Carbonate (CaCO3) is the primary compound of use for use in egg shells. There are some protean found in the membrane that clings to the shell, but I will address those at the end.

The 2 uses for us as vermiculturists are as "grit" to aid in digestion, or as an alkaline PH buffer.

As grit, the shell needs to be small enough to be ingested, but large enough to provide some abrasion in their "gizzard" (I'm sure there is a better term for the worm version of this)

As a ph buffer, you need to consider how rapidly you want it to be able to buffer the ph. It provides this benefit by being almost completely insoluble in near nutral ph water (given strange coaxing in a lab, you can use it to get water, starting at ph7, up to 8.3, but this is only likely under the strangest of circumstances.) As ph lowers, the solubility of Calcium Carbonate increases, neutralizing the acid (and producing some CO2 and salt). The rate it can prodive this buffer is proportional to its available surface area. Thus for slow buffering, say in the garden to counteract local acidic soil, crushed by hand may be ideal. For the worm bin (mine is of a scale to only support 1.5Cubic feet of living space at a time) I want that ph neutralized as fast as it can without being harmful.

I came on here today to see what ideas people had for pulverizing shells smaller than I can get with a rolling pin, but larger than I tend to make with a mortar and pestle (to many years of mindlessly hand grinding spices and various crystals).

Back to the protean. Protean provides a great food source for several types of bacteria, which in turn provide a more varied diet to our worms. However eggs, dairy and meat are at the top of the list of foods that can easily be contaminated with bacteria that can be harmful to us digestive fragile humans. Internal contamination of salmonella of eggs sold in the US is down to about 1:20,000, and even those are typically only dangerous if mishandled. however, if you seed an open egg with any salmonella (a little from raw meat, or even just leaving the egg uncovered on the counter for 4-6 hours) It will be able to produce a colony that can make you very sic, even if you later refrigerate it (that only slows down the reproduction.) Baking the shells to 180 should kill most pathogens, and 250 for 10-15 min should kill anything alive. This would have the additional benefit of partially decomposing (through the maillard reaction aka protean browning) and producing a wide range of compounds, and more importantly for our worms, more surface area for microbes to grow.

Given all that, I will be setting aside my eggs in a bag until I have enough, then baking them, then running them through a yet to be purchased coffee mill (unless I find that the burs in some other mill such as a salt or pepper mill would work better)

Thanks for all your input and ideas, I find this forum extremely helpful!

EDIT: upon further reading, boiling egg shells helps break down any connective tissue in the shell itself (I have yet to verify this through experimentation or well sited sources) but the theory is similar to what happens to bones when you produce a good stock (you can crush those bones to powder very easily.) I will try some boiled then dried vs raw vs baked to see what works best in my newly ordered mill.

This post was edited by TwinHerder on Mon, Apr 21, 14 at 10:59

    Bookmark   April 21, 2014 at 10:24AM
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From what I understood in my readings, the calcium is leeched out into the compost pile. The egg shell itself doesn't not necessarily break down into minute components in 6 or 12 months. If we don't see it, it's because it did have additional breakage and is now small enough and mixed in with clumps of the compost (or as some have said, however it dissolves or divides etc, it is broken down).

It's the same reason that adding egg shell to a tomato planting (or putting shells on top, in case one forgot to do it at planting time) may not necessarily help in that growing season. It still takes a while for the calcium to leech out.

However, that's not to say that the benefits of egg shells should be ignored for compost bins. Go ahead and put some in. Even if you don't totally pulverize it, you will indeed see that when you're ready to use the compost bin, you don't see as much of egg shell material any more, so it somehow did get incorporated into your compost.

    Bookmark   April 21, 2014 at 10:37AM
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Absolutely. The larger the pieces the longer for them to dissolve. Well processed egg shell is EXTREMELY similar to garden lime. If you have large shell pieces that have been "composting" for a long time, you should notice that they are more brittle and pitted. The shell doesn't decompose, it dissolves, like any other crystal. the easiest thing you could do to increase surface area in this case would be to bake / roast the heck out of the shells, removing any organic compounds (membrane etc.) If larger pieces are being used as slow release ph buffer and bio-available calcium. in this case I would put them in a pie pan out on the grill when it is heating up, or once it is done and cooling. Or in the oven during baking a pizza, if the burning egg smell isn't too strong (aka if you wash them out well.)

    Bookmark   April 21, 2014 at 11:07AM
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I also collect eggshells, both for use as grit (sorry EQ2) and as a substitute for agricultural lime. I dry/bake them in the oven, in a large, disposable, aluminum foil pan. I then grind them to powder in MY blender (which I got, together with a food processor from the local Freecycle list). This way, I avoid arguments with my spouse about using her appliances for stuff she considers to be trash (although she does save eggshells for me). I store it in a large shaker, near to my bins and add it from time to time. It seems to disappear quickly enough.


    Bookmark   April 21, 2014 at 1:16PM
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Mortar and pestle.


    Bookmark   April 22, 2014 at 12:19AM
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I put mine in a food chopper but first I microwave them for about 5min. so they are good a dried out.

    Bookmark   April 22, 2014 at 1:05AM
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I too use powdered egg shells in my worm bins. First I give the inside of the shells a bit of a rinse in the sink then place them(concave up) in the oven when cooking something. Then I let them cool and pulverize in a small coffee grinder. Store in a small plastic container and sprinkle a bit on when feeding the workers. Like others, I
use it to reduce any chance of low pH and to provide some grit for the worms.
One question I have is whether the shells ingested by the worms make the calcium in the castings more readily absorbed by plants fed some of the castings.

    Bookmark   January 6, 2015 at 9:29PM
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harry: Why do you rinse the eggshells?

    Bookmark   January 6, 2015 at 10:18PM
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nexev - Zone 8b

With you Otis and I see you have been here for awhile on this one. Good stuff being rinsed away.

Ours get tossed in, no special processing beyond cracking to get the insides out.

Seeing some eggshells in the compost pile doesnt seem to bother me or the worms.

    Bookmark   January 7, 2015 at 12:22AM
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.02 USD more:

I put the shells of two eggs, daily, in a pyrex cup and boil it in the microwave. Drain & add to a bag with a divider : egg shells and coffee grounds and filters . From time to time I powder the egg shells in the processor, & store them in a jar. Powdered shell, & coffee grinds are added to kitchen waste slurry in relatively small ratio for worm bins. Filters go to Earth Machine for precomposting unless needed for a worm bin.

Considerations: Salmonella, tho rare, is still possible so it's worth the nuisance (to me) to sterilize the shells. Egg is an incubator for whatever bacteria is or may be present while the shells sit unused. If I accumulate too much powdered shell,
I sprinkle it on the soil surface. (This is a city and there are lots of walkers past the garden). All the "literature" refers to the worms' gizzard needing grit.

In the tomato test the only tomatoes that got Blossom End Rot were those fertilized with Miracle Gro. A Complete Organic Fertilizer ( a la Steve Solomon ) has a measured balance of minerals. Some minerals "leach out" with rain. Topic in soil forum ?

    Bookmark   January 7, 2015 at 10:43AM
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Besides first drying them out, then cool down, then they go thru two food choppers and by then they are pulverized enough for the worms. But I also sometimes add corn meal to the mix and when I sprinkle this on the bedding and by the next day I always find worms on top gobbling up the mix.

    Bookmark   January 7, 2015 at 12:50PM
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re your question as to why I rinse my shells before drying and grinding, I have read enough posts about the possibility of salmonella so just do it as a precaution. Still would like to hear from anyone who knows if the calcium in the shells is more easily taken up by plants once it has been incorporated into the worm castings? Last season I put powdered eggshells into my tomato pots but still had some cases of blossom end rot ......wondering why??

    Bookmark   January 7, 2015 at 12:59PM
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I've only been worming for a couple of weeks. But, i've been saving egg shells for years. We even have a small eatery in town that saves egg shells for me. I pick them up twice a week.

What i've been using them for is tomato plants. I put about a cup of pulverized egg shells and two tbs of epsom salts in each hole when i plant. I don't think i've ever had blossom end rot since i've been doing this. I plant 90 or more plants per season.

    Bookmark   January 7, 2015 at 4:22PM
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I added some epsom salt and crushed eggshells when I planted toms. last year but still had those BER problems. I only added ~2tbs of the eggshells and I don't think I was grinding up as fine back then. I'll try your idea of 1/2c this year to see if that helps. Thanks for the info.
P.S. Were you growing indet. or determ. toms. and how large a pot do you find works best for you?

This post was edited by harry57 on Wed, Jan 7, 15 at 17:42

    Bookmark   January 7, 2015 at 5:38PM
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there is a high amount of contamination of salmonella (I have found figures of 1:20 up to 1:10) on the outside of eggs, this comes from the birds less than sterile opening. In the US, internal contamination is estimated between 1:20,000 and 1:60,000 eggs. Based on the information on the fact sheet + a little understanding, your options are a sanitizing solution (dehydration or active denaturing of the bacteria's structures) or heat. You could just let is get really dry, but even then it may just go dormant. The problem here is your soil is probably already mildly contaminated. If you are immune compromised, WASH EVERYTHING, and then COOK IT. But the rinsing out the inside is probably not doing anything.

blossom end rot:
to the best of my understanding this is caused by too much acid taken up by the plant.

Calcium availability:
Surface area and Diffusion. Water is going to help break down and dissolve the calcium (95% calcium carbonate, and some calcium phosphate and magnesium carbonate). If the water is not moving, then only the water very close to the egg shell can dissolve the calcium. The more surface area the water is in contact with the solids the faster the water will saturate. So spreading them around will maximize how much water is in contact with the calcium, and breaking up the shells will speed up the rate that that water can saturate with the calcium.

Once the calcium carbonate dissolves it will help hold the waters ph pretty constant. As acids are added they will combine with the calcium, frequently precipitating out as salts, and allowing the water to dissolve more calcium. In salt water aquariums the ph is frequently buffered by LARGE stores of calcium carbonate (shells, and coral)

This is getting into the edge of my chemical understanding and into more grey area, but as far as I understand, the worms do very little digesting of anything going through them other than the bacteria (estimated they digest 50-90% of the bacteria, distributing the rest) What they do is stir the decomposing stuff around, aerate it(making aerobic decomposition easier), and grind it... this will grind the "grit" even smaller, making it more available to the water.
I have NO IDEA what makes the calcium, once dissolved in water, more available to plants. In animals a lot of compounds can only be absorbed when presented in pairs or groups.

    Bookmark   January 7, 2015 at 5:41PM
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thanks for the great info. re the calcium(eggshells) and the plants ability to uptake that calcium input.

    Bookmark   January 7, 2015 at 5:51PM
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This is why I come here... it leads to more research. The following was gained mostly from this amazing article:

it is a little heavy, but was well worth the read.

Bloom rot comes from the spike need of calcium that plants have with rapid or new growth. Even if you normally have enough in the soil, the rapid draw and high need can lead to levels just not being adequate (the water hasn't had time to dissolve it at the rate the plant is demanding it.)

Plants do not need a second mineral / compound to absorb the Ca2 that they need from CaCO3 dissolved in the water.

The maximum total hardness of water can prevent water from holding enough calcium for your plants needs, overly salty soil could cause problems.

Happy worming / gardening :-D

    Bookmark   January 7, 2015 at 6:03PM
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Harry57. I have a regular garden 70x40. I only grow Celeberty and Rutgers. Mostly for canning and to give away.

    Bookmark   January 7, 2015 at 7:12PM
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Last year was really my first serious attempt at growing tomatoes so I guess a little BER isn't the end of the world. I grew in 3-5gal. plastic pots. All 15 of them were either Early Girl and some kind of cherry tomato (both indeterminate).
To try to control the growth they were all pruned down to only one or two main stems and supported using jute twine tied to a support about 8' above the pots. Even then they grew past the top and produced quite well(I guess). I was especially happy since I started them from seed in early April. Any varieties you might recommend for my area - Pac.N.W. zone8?

    Bookmark   January 7, 2015 at 10:04PM
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I have an interest in info on tomatoes to, but I would love to keep this thread to worms and egg shells, I could not find a way to rout tomato posts to a new thread.

I have been considering a similar set up. For my own information;
did you do strait up or at an angle?
did you do 1 row or 2 (2 like a tent shape)
how far apart did you put your containers
What did the roots look like in your pot at the end of the season (heavy root lock? amount of the total volume that was root? etc)

Diagnosis questions:
Do you plan on reusing the same soil next year?
Do you know the ph of your soil and your water sources?
Is egg shell the only Calcium you plan on adding?
Did you notice any patterens with the BER, such as plant, type of plant, height of fruit with BER, or time of growth season of the BER?

    Bookmark   January 8, 2015 at 10:03AM
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Guess I've inadvertently veered off the vermicomposting subject. Go to the tomato forum and I'll try to remember to answer your questions.
c-ya there

    Bookmark   January 9, 2015 at 1:35AM
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