- How to Use Egg Shells in the Garden -

Egg shells are a good source of calcium, as they are composed of mostly calcium carbonate. But putting large egg shells in the garden or composter will not provide readily available calcium that plants need. Large egg shells take a LONG time to break down.

Wash the Egg Shells

Always thoroughly wash the egg shells. I like to place them in a colander in the sink, and spray water with my faucet spray nozzle, to remove any liquid egg.

Heat-Dry the Egg Shells

The shells then need to be dried well. You can place them on a metal pan in the oven 275°-300°F (135°-150°C) for about 20 minutes, or place a heat-safe bowl of egg shells on the floor in front of a wood stove while it's running in cool weather. This is my preferred method, as I don't have to heat up the oven. I recommend heating the shells to kill any potential salmonella, as opposed to just letting them dry without heat.

Finely Crush the Egg Shells

Wait until you have a large amount of shells to crush, so that you aren't dirtying dishes often. I find that the quickest way to crush a large amount of egg shells is by using the food processor. It does a great job crushing them and the parts can be easily washed. Some instructions indicate to use a coffee grinder, but I find a coffee grinder is not easy to clean, and only does small amounts at one time. When using a food processor, I pulse the shells a few times first, and then process on high for about one minute, until the shells are crushed finely and starting to form a powder.

You can add vinegar to the crushed shells to facilitate the extraction of calcium, and then dilute with water to add to the soil or compost. Or, simply add the crushed shells to the soil or compost outside, and work into the soil. Over time, decomposition will break down and release the calcium.

To clean the food processor container, I like to rinse it with vinegar and then wash.