What to Know About Composting Eggshells

Eggshells are a common kitchen waste product. Eggs are used as appetizers, breakfast, and in meals and desserts. You're not alone if you've ever wondered what to do with eggshells after cooking or baking. Often, eggshells go into the garbage. You can't even put them in the garbage disposal!

One of the best and most environmentally-friendly ways to recycle your eggshells is by adding them to a compost pile. This allows you to use your eggshells as fertilizer. Eggshells offer several nutrients for plants, especially calcium, but there are a few things you should do before tossing them in with the rest of your compost.

What Is Composting?

Composting is a way to turn food and yard scraps into fertilizer. When you build a compost pile, you create an environment that lets bacteria, fungi, and other organisms break the waste down in a safe way.

There are two types of decomposition: anaerobic and aerobic. In anaerobic decomposition, the waste is broken down by organisms that don't need oxygen to survive. A by-product of anaerobic decomposition is the release of biogas, which is about half methane and half carbon dioxide. Both methane and carbon dioxide are bad for the atmosphere.

On the other hand, aerobic decomposition involves organisms that need free-flowing oxygen. This doesn't release biogas, making it safer for the environment. The decomposition in a compost pile is aerobic, while decomposition in landfills is often anaerobic. As a result, composting is usually better for the environment.

Composting has other benefits as well. The process:

  • Provides soil with essential nutrients like nitrogen, phosphorus, and potassium
  • Reduces the amount of waste in landfills
  • Reduces the cost of waste management
  • Retains water, which reduces erosion and conserves water

Can You Compost Eggshells?

Egg shells are an excellent addition to a compost pile, as they provide calcium and other key nutrients. 

Whole eggs, egg whites, and egg yolks do not belong in the compost pile, though. Raw eggs have the potential to carry the bacteria Salmonella. Exposure to some types of Salmonella can lead to an illness called salmonellosis, which causes abdominal pain, diarrhea, and fever that may last up to a week. Eggshells generally don't have enough Salmonella bacteria to cause problems.

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Cooked eggs don't belong in your compost, either. As they break down, they can cause your compost pile to have a terrible odor. They can also attract parasites like rodents and flies.

Other items that should not be added to your compost pile include:

  • Black walnut tree leaves and trimmings. Black walnut trees naturally produce a toxin called juglone, which can poison the compost.
  • Coal or charcoal ash. This ash can contain chemicals or metals harmful to compost and plants.
  • Dairy products. Like eggs, dairy products can cause problems with foul odors and attract pests.
  • Fats, grease, lard, and oils. These items are also likely to cause odor problems and attract pests.
  • Fish and meat bones or scraps. Meat bones and scraps can cause strong odors, attract pests, and may harbor pathogens.
  • Pet feces and litter. Pet excrement may contain bacteria, parasites, viruses, and other pathogens.
  • Plants contaminated with illness or insects. Plants that are diseased or infested can then infect other plants.  
  • Yard trimmings that have been treated with chemical pesticides or herbicides. These chemicals can poison plants and the organisms that break down your pile. Check the chemical label for composting instructions.

How to Compost Eggshells

Before creating your eggshell compost, there's one step you need to do to allow the eggshells to give your compost the most nutrients.  

Eggshells are high in calcium, and calcium carbonate makes eggshells strong enough to protect everything inside. This tough exterior means it can take a while to break down; if it doesn't, it cannot offer nutrients to the soil. 

To make the addition of eggshells most effective, the trick is to grind the shells up as finely as possible. Letting them dry out, either by air-drying or by putting them in a warm oven, will make them easier to crush. You can use something like a coffee grinder to crush the eggshells into a fine powder.

Once your eggshells are ready, you can add them to your compost pile. If you haven't made your compost pile yet, they aren't too tricky, so long as you keep a few things in mind.

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The right container and the right location. The ideal temperature range for aerobic decomposition is between 130-140°F (54.5-60°C). To keep your compost pile at this temperature, it can't be too big or too small. Your container can have an open lid or a closed one, but should be between 3-5 feet cubed.

When choosing an outdoor spot for your container, find somewhere dry and shady. Too much sun can dry up your pile, while too much water will make it soggy. 

The right ingredients. For your compost pile to thrive, it needs materials with two key ingredients: carbon and nitrogen. High-carbon items are called "brown" items, while high-nitrogen items are called "green" items. Brown materials include things like dead yard trimmings and paper, and green materials include fresh grass clippings and food scraps.  

If you have too many carbon-rich materials, your pile will be dry. Too many nitrogen-rich materials will make your pile slimy and smelly. To maintain the right part of nitrogen. A good rule is to put in 2-4 parts of brown material for every single part green material. 

Air and moisture. Aerobic decomposition, by nature, needs oxygen. To provide your compost pile with oxygen, there are a few steps you can take:

  • Layer materials to allow airflow
  • Shred or cut your materials into small pieces
  • Turn your pile, either by hand or with an aeration machine

The correct moisture levels are also important. Your compost pile should be about as damp as a wrung-out sponge. If your pile is getting too dry, add some water or more green items. If it's too wet, add more high-carbon materials to manage the moisture.

WebMD Medical Reference

Sources

SOURCES:
Michigan State University: "Adding egg shells to compost."
Minnesota Department of Health: "Causes and Symptoms of Salmonellosis."
Missouri Botanical Garden: "Composting Yard Waste."
Natural Resources Defense Council: "Composting 101."
The Morton Arboretum: "Black Walnut Toxicity."
University of Illinois Urbana Champaign: "Using Eggshells in the Garden and Compost."

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