Sometimes I get questions from gardeners about adding eggshells to the compost bin. Yes, eggshells are appropriate compost ingredients, but they break down very slowly. If you plan to add eggshells to the compost bin, you can grind them up with a coffee bean grinder first if you need uniform, crumbly compost for seed starting. Gardeners with a composting worm bin can use eggshells to provide necessary grit and calcium to the red worms.
Eggs and eggshells have other uses in the flower garden. If you prepare boiled eggs, save the cooking water to use in the garden to revive tired plants, as the calcium and other trace elements provide beneficial nutrients.
Use eggshell halves as temporary seed starting containers. Crack the shells at transplant time to help free the roots.
Place broken eggshells in the flower garden to repel pests, from the lowly gastropod to housecats. Neither slugs, snails, nor cats wish to transverse the jagged barrier a few crushed eggshells provide.
Photo © Anthony Rossos