Egg shells contain calcium.
Plants need calcium.
Lack of calcium causes blossom end rot.
Therefore, adding egg shells to the garden will prevent blossom end rot and feed my plants, and snails won’t cross a line of broken egg shells, right?
The nature of egg shells
When a chicken lays an egg, the shell provides protection. That shell is made up of calcium, magnesium, potassium, sodium, and sulfur, which are all important plant nutrients. The thin, inner lining also contain organic matter, equally important to healthy soil structure. Plus, if you don’t wash your egg shells, they will also contain nitrogen, which is an important plant food.
All of these nutrients would be a great addition to the garden, if the egg shells actually broke down into small enough particles - but they don’t.
Egg shells and decomposition
As stated above, egg shells are designed to provide protection. Unless you are dropping them off the roof of the gym for a high school physics class, egg shells are surprisingly tough. So tough, in fact, that they don’t break down in boiling water. The moisture and microorganisms normally responsible for decomposition do not have a ghost of a chance at breaking down an egg shell in your lifetime.
For example, 170 years ago, Thomas Jefferson raised chickens and ducks. An archeological excavation of the site found that egg shells from those birds were still intact in the soil. This tells us that, no matter how many times you flip that compost pile, those egg shells 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 breakdown enough to be useful to your plants. Unless you have very acidic soil (<6.8 pH) and the egg shells are ground up into a very fine powder, they will add nothing to your soil.
Egg shells and blossom end rot
Blossom end rot is a condition that occurs when plants are unable to move calcium around to where it is needed. This is rarely the result of insufficient calcium in the soil. Most soils have plenty (or too much) calcium already. More often, it is a case of irregular or insufficient watering. Before adding calcium, in any form, to treat blossom end rot, get a soil test from a reputable lab and check your irrigation schedule.
Egg shells as a pest deterrent
Crushed egg shells are also touted as 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 egg-laying season, and some rats, looking for a snack.
Personally, I crush my egg shells and feed them back to my chickens. I don’t know if they actually eat them or not, but I think they do. Just in case, I offer oyster shell, as well.
You can grow a surprising amount of food in your own yard. Ask me how!