Do Eggshells Break Down in Compost?

In an effort to add as much kitchen waste to the compost pile as possible, it was only a matter of time before eggshells in compost came up. Since most of the kitchen scraps that go into our compost piles are plant materials, the mineral composition of eggshells is foreign enough to require some research. 

Should Eggshells Go in Compost?

The main purpose of our compost is to break down organic matter into finely ground soil that is good for all garden applications. Eggshells should go into a compost pile, but certain steps should be taken to make the composting process easier. 

To get finished compost and organic material for your garden, eggshells should be composted with other food scraps and kitchen waste. Plenty of carbon and nitrogen needs to be mixed with eggshells to allow the minerals to break down.

The temperature of a compost pile also helps determine if eggshells should be composted. The hot composting process will kill any harmful pathogens on eggshells and food waste and also reduce the time it takes for the shells to deteriorate. A cold compost will not kill bad bacteria directly and will take much longer to break down. 

How Long for Eggshells to Decompose?

The time it takes eggshells can be difficult to determine. It takes about 1 year for a large chunk of eggshell to disappear and no longer be noticeable in the compost pile. After another year, the minerals in the shell will have broken down to completely plant-accessible nutrients. 

Chunks of eggshells in the soil are a long-term reliable source of calcium that can help certain plants thrive. They do not need to be completely decomposed before they start to increase the soil calcium levels. Instead of adding eggshells to the compost, you can consider planting them with new plants to give the roots a future supply of nutrients. 

Eggshells can be decomposed in an outdoor compost pile for several years while being sifted out of the final compost product. Good bacteria in the compost will stick to the eggshells and innoculate future organic materials. The slow decomposition of eggshells is not necessarily a bad thing.

How to Speed Up Decomposition in Compost?

If you are in a hurry to get your eggshells into finished compost fast, then there are plenty of options for that as well. Speeding up the decomposition of eggshells does not decrease the quality or quantity of nutrients available to plants it only supplies it sooner. 

Speed Up ByHow To BreakdownHow to Apply Benefits to Soil
Soaking EggshellsPut eggshells in hot water and let sit overnightScatter-soaked eggshells around plants and in potsAdds moisture and calcium to the soil, a stable mulch option
Baking EggshellsHeat in a warm oven at 225℉ for 20 minutes Crush into small chunks and bury with new plantingsLong-term supply of calcium deep for mature roots
Grinding EggshellsPut eggshells in a coffee grinder and pulverize. Sprinkle granular powder eggshells on top of the soil or amend the soil with itGround eggshells are an immediate source of calcium for plants
Acidic SoilBury eggs in acidic soil to increase the decomposition ratePlace in soil or compost and add agriculture limeIncreases acidity speeds up decomposition and increases magnesium and calcium
Hot CompostingBuild a proper compost pile and turn it every 2 days to kill bad bacteria and weed seedsBury eggshell pieces in compost and let heat break them downKills salmonella bacteria and reduces the risk of salmonella in future plants

Soaking Eggshells

The soaking process can clean the shells and reduce salmonella contamination. The wet eggs can add water to the compost pile and deters pests. This method will not reduce compost time by much but can help with nutrients and moisture for tomatoes and other vegetable plants.

Baking Eggshells

This is an effective way to make the eggshells more brittle and reduce the risk of disease. Baking eggshells for a short period of time is the first step to making eggshell powder. Heat is the only thing that can reliably kill types of salmonella from bacterium salmonella.

Grinding Eggshells

This is the fastest way to make eggshells into vegetable garden compost. The powder mixes easily with finished compost and immediately gives a calcium boost to plants. Ground eggshells have less of a chance of being infected with salmonella bacteria. Grind eggshells before composting to speed it up!

Acidic Soil

A common building material in the form of agriculture lime can be added with eggshells to the compost to reduce the pH. Increasing acidity can reduce pests and help with gardening issues. The lime solution per plant should be calculated to avoid nutrient lockout.

Hot Composting

This method of composting gets hot and can break eggshells and other large pieces of compost in a short amount of time. It kills a lot of pests, pathogens, and weed seeds and reduces the food sources for bad bacteria. Eggshells break down faster in high heat with appropriate moisture levels. 

What Are the Dangers of Composting Eggshells?

There are some dangers to composting eggshells that can lead to health risks or a reduced quality of compost. The most important thing to remember is that compost should always be mature before being applied directly to edible leafy greens in the garden to prevent illness. 


Eggs that come from a chicken ovary can contain fecal matter or other impurities. These can harbor salmonella bacteria which can make humans very sick if ingested. Most of these bacteria have been cleaned off of eggs in the egg industry before they leave the farm, but sometimes they persist. Clean eggs before packaging if selling to friends or neighbors to avoid making them sick. 

It is important to have a method to clean home-laid eggs, or ones from friends are cleaned before using them to avoid these issues. Once the mineral product, eggshell, has been cleaned, it can be added to the compost safely.

The sharp edges of the eggshells can hurt your hands if you are working in the compost without gloves on. The large chunks can slow down the decomposition process, and over time too many eggshells and not enough organic matter can make poor-quality compost. 

What Are the Benefits of Composting Eggshells? 

Despite the drawbacks, there are many advantages to composting with eggshells. Eggshells can supplement your soil flora, especially when it is coarsely ground. Finely ground shells may dissolve too quickly, but the coarsely ground eggs will last a while as a slow-release fertilizer and minerals for microorganisms. 

Eggshells can also help kill pests in the garden that attack your plants. Snails and slugs, and any other soft-bodied pests are injured when they crawl or pass over the jagged eggshells. The eggshells cut the slugs and common pests and protect your plants. The shells act like diatomaceous earth and can keep pests at bay for as long as the shells stay put. 

While the shells are protecting the plants in the garden, several milligrams of calcium are leeching into the soil, helping plants find more nutrients in a shorter period of time. The liquid calcium solution for watering down eggshells doesn’t take away from its effectiveness as a pest deterrent for pest control and will still be sharp enough for pests for many months.  

How to Effectively Use Eggshells to Improve Your Garden Soil?

Eggshells can add a lot to garden soil but should be composted with yard waste and paper goods. The brown material of paper helps create the heat that will break down the eggshells faster. Paper can be substituted for other brown materials like dry leaves and cardboard. 

Chicken eggshells can be prepared for compost in a few different ways to improve your garden soil. Deciding how you will use chicken eggshells will determine how you prepare the shells for use.

Compost – Raw eggshells can be put in compost to deter animal pests and improve the soil. Little needs to be done to prepare the raw shells for compost, but the more they are crushed, the faster they will break down. In an eggshell decomposition study, homemade eggshell powder broke down faster than shell chunks in a healthy compost.

Raw eggshells need to be made into crushed, heat-dried eggshells in order to break down faster, according to an eggshell decomposition study. Homemade eggshell powder is an excellent source of calcium in eggshells for food crops. 

Make sure to focus on compost hygiene and add the eggshells in small batches to keep bad bacteria at bay. Then there will be no worries about salmonella or the danger of salmonella in future food crops. Use high-quality compost ingredients to make sure you give your garden the best nutrients.  

Soil Amendment – If you want to skip a batch of compost and use your crushed, heat-dried eggshells directly in the soil, you can as well.  Ground eggshell meal can be placed in planting holes for tomatoes and bell peppers to prevent blossom end rot. Ground eggshell meal can also be sprinkled in potted plants to boost calcium and stem strength for several months.  

Grinding and amending soil with eggshell fragments is a great option if you have an abundance of eggshells. You can also use eggshells with soil as containers for seed starting if you need seed pots. This is great for growing tomatoes from seed as you can plant it all together for an incredible source of calcium when tomatoes need it most.  

Pest Control – Common scrap materials around plants can cause pests to come by, but the thicker shells of eggs can kill soft bodes, insects, and slugs. Put thicker shells around the bases of plants to keep pests away from new seedlings and sensitive plants. Eggshells for pest control are also a natural source of calcium.