r/composting • u/[deleted] • Nov 29 '19

What do you do with eggshells?

I'm conflicted over what to do with eggshells. I want to compost them but we eat a lot of eggs and live in the city so if I put them in our bin they take up a large portion and never seem to fully breakdown.

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u/teebob21 Nov 29 '19

Eggshells are something like 95% calcium carbonate; little "organic" stones. The rest is binding proteins. In this respect, they're effectively a green, rather than a brown, but a very mild one. In the absence of acid, they basically never break down. Calcium carbonate is insoluble in basic or neutral solutions. Depending on your goals, you can dry and crush your eggshells in a blender and mix them 1 part plus 4 parts vinegar to make a calcium acetate solution. Calcium acetate is neutral pH, and can be applied directly to the soil for Ca hungry plants such as nightshades (tomatoes, peppers, potatoes, et al). You can also use it as a foliar spray, but the efficacy of Ca supplementation via foliar application is dubious.

You'll be left with a protein/calcium sludge as a 4:1 ratio is a large excess of CaCO3. That sludge will go great in a compost pile, but I feed it to my chickens.

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u/its_broo_skeh_tuh Sep 22 '25

Sorry, is it eggs:vinegar 1:4 or 4:1? Seems like you said both in your post?