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From the Rotline: How should I prepare eggshells to add to my compost?

Rotline Question:  How should I prepare eggshells to add to my compost?

Answer: Eggshells are a great addition to any compost bin, adding calcium to your finished product and keeping yet another resource out of the landfill.

If you are looking to add eggshells to your traditional compost bin, you can determine how much, or how little, work you want to put into preparing the shells. You do not need to crush the eggshells before adding them to your compost pile, but doing so will speed up the breakdown of the shells in the pile. Simply crush them with whatever garden tool is convenient and make sure to cover with a layer of browns to deter pests.

If you plan to add your eggshells to a vermicompost bin, I suggest ensuring the shells are not just crushed -- but ground -- in order to properly serve as a source of grit for your worms. To get a ground consistency, you will need to ensure the shells are very dry. The first step is to rinse the shells and place them in a bowl or on a baking sheet for a few days to dry, or you can avoid rinsing and speed up the process by baking them at 200° F for 20-30 minutes. Once the eggshells are dry, you can grind them using a coffee grinder, blender, food processor or mortar and pestle until you have a powder with particles no larger than grains of sand. Simply sprinkle the ground eggshells in your worm bed for your wigglers to enjoy. 


Written by 2019 (City of San Diego) Master Composter Grad Kim-Ashleigh Mostert-Freiberg