Do Eggshells Increase the pH of Soil?

Suppose you grew up in a household that either grew their vegetables or was very conscious about the amount of waste they created. In that case, you might remember your parents being insistent about not throwing the eggshells out. Instead, your parents may have thrown them in a container to be later used for compost, and you might be curious about what eggshells did to the soil. 

Eggshells can increase the pH of soil but only upon contact. The calcium in the shells is a chemical that can increase your soil’s pH for the moment it integrates with the soil. However, the amount of calcium these eggshells have is generally not enough to completely change soil pH.

Understanding how eggshells and other ingredients you might use in your compost is key to knowing exactly how your compost impacts your soil. Let’s take a deeper look at eggshells and how they affect your soil, including how they impact pH and what nutrients eggshells provide for the soil. I will also discuss the benefits and downsides of adding eggshells to your compost.

Eggshells’ Impact on Soil pH

Think of a patch of soil. Within that one-square-foot (0.09 square meters) area, there are likely thousands of different types of microorganisms breaking down organic matter, hundreds of various nutrients to sustain plant life, and plenty of moisture. 

Now, imagine digging a small hole and burying an eggshell. Though packed with nutrients, that eggshell is incredibly fragile, biodegradable, and small. How much of an impact will that one eggshell have on soil pH?

Eggshells, being so tiny, generally don’t have a significant impact on soil pH unless the pH is incredibly low. At high volumes, eggshells are likely to moderate pH levels. As the eggshells dissolve some of the acids, it will raise the soil pH. If the soil pH is too low, the eggshells probably won’t have much of an impact.

Imagine dropping a drop of red food coloring in the pacific ocean. One drop of food coloring probably won’t have any impact. Even if it does, it will be minimal and last for a short time.

Now imagine a drop of food coloring in an ice cube tray. It would make for a bright pink ice cube. The same is true for eggshells and soil acidity. If the soil is too acidic, eggshells are insufficient to raise the soil pH. Consequently, large numbers of eggshells can increase the pH in a small patch of soil.

The moderating impact is due mainly to the calcium in the shells. Like a human bone, eggshells are a great source of calcium, which, when combined with water and air, can neutralize acids and increase pH.

However, it is essential to remember that it takes a long time for eggshells to decompose and release enough calcium to alter the soil pH. You will need plenty of finely crushed egg shells before you can see any significant change in soil pH.

Benefits of Eggshells in Soil

As mentioned previously, eggshells are almost entirely calcium. It means that, while they lack some essential components needed for plant growth, they can help to create incredibly durable, long-lasting plants. 

Calcium is essential for creating the cell walls of plant cells. These cell walls help to protect important components of plants like chloroplasts and mitochondria, which produce the energy plants need to undergo photosynthesis.

Additionally, the calcium in eggshells plays a vital role in ensuring that plants receive plenty of water, but not too much. The plant’s cell walls monitor the amount of water received through osmosis and stop the process from occurring if too much water is absorbed. 

Another critical feature of the cell wall is the ability to fight off harmful bacteria that might try and hurt the plant. The cell wall is, quite literally, the barrier that divides the inside of the cell from the outside of the cell. Like an old city, the walls prevent harmful material from entering the cell, making it critical for cell survival.

One more essential benefit of placing eggshells in your soil is preventing small and large pests from harming your precious plants. As eggshells decompose, they produce a smell that larger animals like deer and bears hate. 

Crushed eggshells are also used as a snail and slug repellent because the rough surface is too uncomfortable for soft-bodied animals to crawl or slither over. Spreading them in a circle around your plant can keep snails and slugs away.

Composting Eggshells

While eggshells are great for soil in isolation, they can be even better when paired with other organic matter in the form of compost. When added in sufficient amounts, eggshells can even raise the pH of your compost.

Composting is a process used to recycle organic materials that might not be suitable for human or animal consumption. Much of the waste humans produce comes directly from nature. Grass clippings, banana peels, raked leaves, and human feces are all considered organic material.

This is not to say that all organic materials need to be reused or are safe for reuse (i.e., human feces). But much of what we regularly throw away could be reused by nature. 

Soil is full of decomposers, the lowest level of the food chain. Decomposers, like worms, bacteria, and some fungi, eat organic matter. These microorganisms break organic matter down to release the important nutrients in a simplified form that plants can use.

Advantages of Adding Eggshells to Compost

Aside from leaving essential nutrients in the soil that allow plants to grow, compost can also have a number of other positive effects on your soil. Adding crushed eggshells to your compost can help improve the quality of the finished product.

Compost Can Improve Soil Density

Compost can help balance soil density. It is an excellent amendment for soil that is either too loose or too dense. Using plain crushed eggshells cannot achieve this. They may even make your garden soil look unsightly. That’s why it is best to add egg shells to your compost pile.

However, despite the presence of decomposers in the compost pile, they might not be able to break down the eggshells as quickly as the other organic materials. It would be best to manually crush the eggshells and spread them evenly in the compost pile.

Can Raise the Compost’s pH With Eggshells

While eggshells cannot quickly and significantly change the soil pH, adding them to a compost pile will result in a product that helps bring the soil to a relatively neutral pH, especially if your pile has plenty of acidic components.

When the compost has a low pH, some gardeners add lime to increase the pH. Egg shells are primarily made of calcium carbonate, similar to lime. However, be careful about adding too many eggshells into the compost pile, which can result in nitrogen loss.

Eggshells Can Add More Nutrients

Instead of placing the eggshells directly into your garden soil, you can add them to your compost pile. While the shells are predominantly calcium, the yolk residues in the eggshell are nitrogen-rich, and they can be an excellent addition to your compost.

When you add finely crushed eggshells into your compost, the decomposers can break them down more quickly to incorporate their nutrients with the other organic materials. The final product of your compost will be nutrient-rich, making the soil healthier and encouraging your plants to grow stronger.

Downsides of Eggshell Composting

You should ensure that your compost pile is safe from rodents, such as rats, since eggshells can be attractive to them, especially if there are egg yolk residues on the shells. Crush the eggshells as finely as possible and bury them in the middle of your compost pile.

Another concern is that some eggshells may contain harmful microorganisms, such as Salmonella, which cannot be broken down during the composting process. They might survive in your garden and contaminate edible plants.

Final Thoughts

Eggshells are a great additive that can be added to soil to help neutralize acids and bring soil to a neutral pH. However, it can take a large number of crushed eggshells and a pretty long time before you can see any significant changes.

Full of calcium, eggshells make the plant’s cell walls incredibly strong, helping them to become more durable and last under adverse conditions. When combined with compost, eggshells can help to make your soil great for sustaining plant life.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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