What to Know About Composting Eggshells

 What to Know About Composting Eggshells

Eggs are an amazing work of nature, produced ideally in the oviducts of birds (and platypuses), but most people think of eggshells as a by-product: a piece of waste that ends up in a landfill. If you've always wanted to keep your eggshells from falling out, let's take a look at how to add them safely and effectively to your compost pile.

The first thing to know is that compost does not break eggshells. However, by crushing it and working it into your compost pile, you'll end up with a humus-rich product (from decomposed organic matter) that contains extra calcium (from eggshells). They should be cleaned to prevent them from attracting rodents and other creatures, and disinfected to kill any potential bacteria.

Eggshell fertilizer

Eggshells can be safely added to your compost.
My wife's grandparents in Germany always composted eggshells, and while the glory of their garden is a testament to gardeners, the eggshells certainly didn't suffer.

Here are some of the benefits of composting eggshells:

Reduces organic waste in landfills.
It adds calcium to the soil.
Contains trace amounts of other minerals
It can help deter slugs and snails
Good for insects.

Although whole eggshells can be tossed into the compost pile, they will do little for your garden unless they slowly decompose over the years. Eggshell has to be prepared to be really useful. To get the most out of compost, we need to understand what eggshells are and what they do in compost.

It's all about eggshells

A chicken egg contains about 94% calcium carbonate, 1% trace minerals and 5% organic matter.
When broken down, each shell contains approximately:

2,000 - 2,400 mg calcium
16.5 mg of phosphorous
16.5 mg of magnesium
Additional minutes:

Incredibly strong eggshells. When they are healthy, it is impossible to crush them with your hand, and they are able to support the weight of the car when they stand on end.

Even when it does crack, the eggshell is very tough. Archaeologists in England have unearthed four chicken eggs from an ancient Roman site where the eggs had been preserved for 1,700 years. The eggs were so perfectly protected by their shell that they were rotten and, when broken, gave off an unpleasant odor.

In the deserts of Israel, ostrich eggs were found around an ancient Bedouin bonfire. The shells looked like they had just cracked, yet they had been buried under the sand dunes for over 4,000 years.
Garden moth eggshells were buried in the garden and watched every year for five years to see how they broke in an intriguing experiment. The organic membrane inside the shell degraded during the first year, but there was practically no additional breakdown after that.

Because calcium carbonate decomposes quickly in acid, eggshells will decompose quickly in acidic soil. However, the pH must be close to 4.0 to make a significant difference and very acidic to grow a healthy lawn.

How to compost and use eggshells in the garden

When the eggshell is ground, the calcium mixes with the soil and becomes available to plant roots. Here are some tips for preparing eggshells for composting:

Wash the shell to remove any remaining egg bits. These egg fragments will attract animals to the compost pile and create an ideal breeding ground for mold and bacteria. At this point you can remove the membrane from the inside of the casing, but that seems a little tricky to me.
Bake the eggshell at 250 degrees Fahrenheit for 1 hour. This will kill any bacteria and dry the crust so it breaks easily. They will be finer in compost and more effective in soil.
Grind the peel into a fine powder by grinder. While you can crack them by hand, studies have shown that finely ground eggshells release significantly more calcium than hand-crushed eggshells in the first few years. Of course, this step is optional, but you'll see more immediate benefits for your lawn by grinding it first.
Add the powder granules to compost or soil. Adding the shells to your compost pile will create a calcium-rich soil conditioner, or you can add them to the soil as needed. It will not decompose differently than the soil in your compost pile and will not affect your plants.

Concerns about eggshells in compost

Some people are concerned about eating eggshells, such as:

Possible salmonella contamination
Ugly (although I love seeing natural organics in my garden)
Attract mice, rats, dogs, snakes, birds and other animals
Fortunately, these problems are easy to mitigate.


Salmonella can be transmitted when eggs are laid or through contact with contaminated feces. The bacteria will transfer the bacteria to your soil and possibly to your fruits and vegetables. These bacteria can live in the soil for up to a year, so it is best to kill the bacteria before adding the pellets to your compost.
To kill salmonella on eggshells, heat them to a temperature of at least 160°F (71°C). Baking them in the oven, as mentioned above, is a great way to dry out the crust and kill salmonella at the same time. Some people employ hot composting to destroy these germs, but this is a riskier endeavour since you can't ensure that all eggshells will reach the proper temperature.
The CDC has more information on safe handling of eggs with salmonella.

Attract Animals

I try to avoid calling unwanted critters "pests," but they can certainly be a nuisance when you don't want them to, and eggshells can attract critters to your compost pile. Depending on where you live, you may end up with rats, mice, dogs, snakes, crows, magpies, just to name a few scavengers that visit your compost in search of leftovers.
However, it is very important to remember that these animals do not eat the shell, but rather any pieces of the egg that are still attached.
Washing your eggshells thoroughly before composting should eliminate the majority of uninvited guests.

Make the most of our waste

Knowing that eggshells are very slow to decompose may deter many of us from adding them to our compost. However, even if we got rid of it entirely, we would still be reducing the amount of waste that would have ended up in the garden. And it will decompose over time when we get rid of the soil and plant it.

We're often drawn to quick and easy fixes for our garden, so waiting for eggshells to crack seems like a waste of time. Fertilizing is one of the best ways we can improve soil naturally, but building soil is a lifelong project, and adding eggshells today may be just what our plants need for years to come.

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