Eggshells

Eggshells contain calcium. Plants need calcium. Lack of calcium causes blossom end rot. Therefore, adding eggshells to the garden will prevent blossom end rot and feed my plants, and snails won’t cross a line of broken eggshells, right?

​Wrong.

The nature of eggshells

When a chicken lays an egg, the shell provides protection. That shell consists of calcium, magnesium, potassium, sodium, and sulfur,. All of those are valuable plant nutrients. The thin inner lining contains organic matter that contributes to healthy soil structure. Also, if you don’t wash your eggshells, they will contain nitrogen, another valuable plant food. 

These nutrients would be a great addition to the garden if the eggshells broke down into small enough particles - but they don’t.

An egg in the hand...

Eggshells and decomposition

As stated above, eggshells evolved to provide protection. Unless you are dropping eggs off the gym roof for a high school physics class or cracking them against your kitchen counter, shells are tough. They don’t even break down in boiling water. The moisture and microorganisms responsible for decomposition do not have a ghost of a chance of breaking down an eggshell in your lifetime.

For example, 170 years ago, Thomas Jefferson raised chickens and ducks. An archeological excavation of the site found that eggshells from those birds were still intact in the soil. So, no matter how often you flip that compost pile, those eggshells will never significantly improve anything in the garden.

Even if you let them dry and crush them into smaller bits, those bits are very unlikely to break down enough to be usable by your plants. Unless you have very acidic soil (<6.8 pH) and the eggshells are ground into a fine powder, they will add nothing to your soil.

Eggshells and blossom end rot

Blossom end rot is a condition that occurs when plants cannot move calcium to where it is needed. Calcium is an immobile nutrient because it takes a lot of water to move it around inside a plant. Calcium shortages can be due to low calcium levels in the soil [generally east of the Rocky Mountains] or irregular irrigation habits [generally west of the Rockies]. Get an inexpensive lab-based soil test from your local university or soil test lab to learn exactly what your plants are dealing with.

Eggshells as a pest deterrent

Crushed eggshells are said to be a barrier against slugs and snails, cutworms, and even deer. Those claims are false. The only thing you might find is some birds will be attracted to the shells, either through natural curiosity or as a calcium source during the egg-laying season, and some rats looking for a snack.

I crush my eggshells and feed them back to my chickens. I don’t know if they eat them, but I think they do. Just in case, I offer oyster shells, as well, and water my tomatoes regularly.