Eggshells are great for compost because they add calcium and will feed your plants once they have been broken down. Eggshells do not need to be washed before adding them to your compost. Any bacteria left on the inside or the outside of the egg will be killed off by the composting process or will even out in the compost finding balance with natural soil bacteria over time.
I have been adding eggshells to my compost pile for many years without any issue. A few eggshells per week will be a small percentage of the mix and will not cause any imbalance of bacteria or any harm to your plants.
A Michigan University article1 supports this stated that over time the bacteria balance will even out across the compost mix and your soil.
If you are concerned the hot composting method kill off any bacteria left in your eggshells. You can bake your eggshells in an oven before composting to break them down into smaller pieces and kill of any bacteria.
This article will explore more about washing eggshells before composting, how to bake them to break them down quicker and some easy composting tips.
How to compost eggshells
Here are some easy tips to help you compost eggshells a quickly as possible. You do not need to wash eggshells before composting them but you can if you like. This will remove any residual albumin left in the eggshell to help to avoid them attracting ants.
1. Crush eggshells with a spade
The easiest way to add eggshells to your compost is to scatter the eggshell halves over the top of the compost. You can then use your spade to crush the eggshells into smaller pieces. The pieces will usually end up ½ an inch or less in size which will help them to break down.
2. Dig eggshells into the compost
Throw the eggshells on top of the compost pile. You can crush them with a spade and then use your garden fork to dig them through the compost. Another option is to use a compost stirrer to mix it through so that they break down faster.
3. Hot compost your eggshells
Hot composting will kill any salmonella left on the eggshells as a hot composting pile will heat up to 140-160 degrees Fahrenheit. Hot composting is a process where large amounts of organic matter are piled up at the same time. The pile will need to be at least 4x4x4 foot in size.
The pile needs to be turned over often, every 1-2 weeks and the mix will need to be around 1/3 green material to 2/3 brown material. Mix the eggshells through to compost pile at the beginning. The eggshells will be broken down as you mix the compost and the rest will be broken down by soil bacteria.
There is the chance that larger pieces of eggshells will still be visible after the compost pile has broken down. This is fine and won’t harm your plants if you dig it into the soil. It will continue to break down over time and add calcium to your soil.
If you want finer pieces of eggshell then follow the baking method before adding the shells to your compost bin.
For more on hot composting, check out my article here: Why does a compost heap get hot? + the secret ingredient
How to bake eggshells before composting
To help eggshells break down quicker and avoid any large pieces leftover in your finished compost you can follow this method.
Baking your eggshells will dry them out and enable you to break them into tiny pieces. This means that they will break down quicker or the pieces will be too small to see. Soil bacteria will move in to digest the eggshells releasing the nutrients into the soil making it available to your plants.
Here are the easy steps to bake your eggshells ready for your compost bin.
1. Collect your eggshells
Collect enough eggshells to cover a small baking tray. You can do this process as often as needed but it is good to have enough eggshells to cover a tray and make heating up your oven worthwhile.
2. Preheat your oven to 356 Fahrenheit (or 180 degrees Celsius)
3. Scatter the eggshells over the baking tray evenly spaced
4. Bake eggshells in your oven for 10 minutes
After eggshells have been baked any albumin leftover will turn brown and dry up.
5. Crush them on the tray with a rolling pin
This process can be quick to gently break them down or you can grind them to a fine powder. The smaller the pieces are, the quicker they will break down in your compost.
You can crush the eggshells up as small as you like. You can roll a tin over the pieces to crush them even further.
Smaller eggshell pieces will break down quicker in your compost pile.
6. Scatter them over the top of your compost pile
The pieces of eggshell will be small after drying them out and crushing them. You can sprinkle them over the top of your compost pile. It is a good idea to dig them into the mix to help them to break down and stop them from blowing away in the wind.
These eggshells can also be added to your worm farm. The soil bacteria and worms will mix the eggshells through the worm castings and make the calcium and other nutrients available to your plants when mixed through your soil.
You can break down these eggshell pieces in a hot or cold composting pile or bin at home and they make a great addition to your yard.
Do you need to wash eggshells before composting? | Summary
You do not need to wash eggshells before composting if they only make up a small percentage of your compost mix. Any bacteria left in the eggshells will balance out with other soil bacteria populations over time and will not affect your plants.
You can bake your eggshells to remove any bacteria before composting. You can also break them down in a hot composting system as another way to remove the bacteria.
Adding eggshells to compost, Michigan State University, 2013, accessed 22/2/22, https://www.canr.msu.edu/news/adding_eggshells_to_compost