can you compost eggshells?
Yes, and grind them first — whole shells are often still recognizable when everything around them has become finished compost.
breaks down in Weeks ground to powder, a year or more left whole
which bins can take it?
- hot pile yes
- cold pile yes
- worm bin yes
- bokashi caution
- tumbler yes
- curbside yes
- worm bin: Ground shell doubles as gizzard grit and keeps bin pH from sliding acidic.
- bokashi: Nothing about mineral shell ferments — it rides through the bucket unchanged and still has to be buried afterward.
why?
An eggshell is about 95% calcium carbonate, and no microbe has an enzyme for mineral, so shells only shrink as pile acids etch their surfaces. That makes it a surface-area game: powdered shell disappears in a season, halves can outlast two or three batches. The thin membrane inside is the only part that decomposes biologically.
how to prep it
- Rinse out the white so the collector doesn't smell
- Dry the shells on a rack or in a cooling oven
- Crush to a coarse powder in a blender or under a rolling pin
watch out for
- Eggshell calcium releases far too slowly to rescue a tomato from blossom-end rot mid-season — that problem is usually uneven watering, not soil calcium.
- Rinsed shells are safe, but unrinsed raw shells can carry Salmonella; a pile holding 131°F for three days clears it, a cold bin may not.
often confused with
- Oyster Shells — Same chemistry, different armor — oyster shell takes years where eggshell takes months.
quick answers
Do I have to bake eggshells before composting them?
No — baking mainly dries them so they crush cleanly and don't stink on the counter, and a rinse plus a windowsill does that for free. The one reason to bake: ten minutes at 250°F also kills any Salmonella riding on the shell, which matters if your bin never heats up or you sprinkle ground shell straight onto beds.
Do eggshells keep slugs out of the garden?
Barely. Extension trials have repeatedly found crushed-shell rings a poor barrier — slugs cross them on damp nights without much trouble. Compost the shells for the calcium and use bait or copper for slugs.