How long do eggshells take to compost?

QUESTION: How long do eggshells take to compost?

ANSWER: Eggshells typically take a remarkably long time to compost, and though they supposedly add calcium to the soil when they finally do decompose, it is not recommended to add eggshells to your compost pile because they take so long to break down, which can slow the composting process down, and because they are known to attract rodents and other pests to the compost pile.

The one exception, where a study showed that eggshells actually can break down in a reasonable amount of time in certain environments, is when finely ground eggshells were added to an acidic soil base.

In a study in which large eggshell pieces were buried in a balanced soil medium and dug up after one year, examined, reburied, and dug up to examine again after three years, the eggshells showed no signs of decomposition after either one or even three years underground.

So, it’s hard to answer exactly how long it will take for eggshells to compost, but based on the three year study, it seems that eggshells decompose incredibly slowly and possibly even not at all.