Yes, eggshells can be composted and are beneficial for adding calcium and other nutrients to the soil. Eggshells are one of the many food scraps that can be composted at home to enrich garden soil and reduce waste going to landfills. Composting eggshells provides a sustainable way to recycle their nutrients and return them to the earth.
Why Compost Eggshells?
There are several benefits to adding crushed eggshells to your compost pile:
- Excellent source of calcium and other minerals. Eggshells are over 90% calcium carbonate. As they break down, they slowly release calcium and trace minerals that are essential for plant growth and development. Calcium strengthens cell walls, aids plant roots and enzyme functions, and improves stress resistance.
- Helps balance pH levels. Most plant materials composted, like fruit and vegetable scraps, coffee grounds, and grass clippings, are acidic and lower pH over time. Eggshells are alkaline and counteract acidity to help keep compost pH neutral.
- Provides structure and airflow. Crushed shells add coarse texture that improves aeration and allows oxygen circulation in the compost pile. Good airflow helps beneficial microbes thrive.
- Attracts earthworms. The gritty texture of eggshells is ideal for earthworms. Their tunneling aerates the compost and they excrete nutrient-rich castings as they feed on decaying organic matter and shells.
- Enriches soil when applied. Finished compost containing eggshells is an excellent fertilizer. The calcium makes nutrients more available to plant roots. Compost also improves soil structure, fertility, and water retention.
How to Prepare Eggshells for Composting
Eggshells should be thoroughly washed and dried before adding to compost to prevent odors or attraction of pests. Follow these steps:
- Rinse any raw egg residue off used shells. Hot water helps remove membrane and proteins.
- Allow shells to air dry completely or place in a warm oven until dried and brittle. Remove any attached paper liners or stickers.
- Crush shells into smaller pieces or grind to a fine powder or grit using a mortar and pestle, rolling pin, food processor, or blender. The smaller the pieces, the faster they will decompose.
- Do not compost raw eggs, egg whites, egg yolks, or uncooked shells as they can pose risks from bacteria like Salmonella. Only compost cleaned shells.
- Microwaving crushed shells for 60 seconds can kill any lingering bacteria. Let shells cool before adding to compost.
How to Add Eggshells to Compost
- Mix eggshell pieces throughout compost bins or piles rather than in dense layers. Blending shells allows better contact for decomposition.
- Pair nitrogen-rich “green” materials like fruit/vegetable scraps, grass clippings, and coffee grounds with carbon-rich “browns” like dried leaves, sawdust, or shredded paper.
- Bury shells 6-12 inches deep in compost piles or bins. This prevents odor and deters rodents from digging for shells. Monitor pest activity.
- Limit eggshells to 5-10% of total compost volume. Excess shells can slow decomposition and leach calcium. 2-3 crushed shells per gallon of compost is ideal.
Composting Methods for Eggshells
Backyard compost piles: Layer crushed shells between organic materials. Turn pile periodically to mix and aerate.
Enclosed compost bins: Add a bit each time you deposit food scraps. Tumbler bins make turning easy.
Vermicomposting (worm bins): Mix fine eggshell grit into bedding. Worms will break shells down within 1-2 months. Provides calcium needed for worm reproduction.
Bokashi composting: Inoculate crushed shells with bokashi bran and let ferment anaerobically before burying in soil.
How Long Do Eggshells Take to Decompose?
Eggshell decomposition time depends on the size of pieces and composting method:
- Powdered shells break down within 2-4 weeks
- Small grit sized pieces take 2-3 months
- Larger crushed fragments may take 6 months or longer
- Whole shells can take over 12 months to fully decompose
Worm composting speeds up the process to just 4-6 weeks for grit and 2-3 months for larger pieces. Turning and mixing piles also hastens shell breakdown.
Signs Eggshells Have Decomposed
It can be difficult to see if shells have fully broken down in compost. Look for these signs of complete decomposition:
- No longer see white shell fragments, only tiny gritty specks
- Shell particles have darkened or discolored
- Materials have softened and are no longer sharp or abrasive
- Calcium has been released into the compost
- Earthworms and fungi have consumed the shells
- Compost has finished curing and maturing
Using Finished Eggshell Compost
Mature compost containing a mineral boost from eggshells has many uses:
- Mix into garden beds and potting soil as a slow-release fertilizer before planting. Provides long-term calcium and enriches soil.
- Topdress lawns, flowerbeds, and roots of trees/shrubs. Sprinkle a thin layer around bases to feed plants gradually.
- Add to seed starting mix for seedlings and transplants. Calcium improves germination and healthy growth.
- Side-dress growing vegetables by working aged compost containing eggshells into top few inches of soil mid-season. Bolsters fruiting.
- Improve soil texture for containers by amending with up to 20% finished compost to aid drainage and water retention.
The nutrients from composted eggshells continue working in the soil for months, even years, after application. The benefits to plant and soil health make them a valuable addition during composting.
Other Uses for Eggshells in the Garden
Beyond adding shells to compost, there are other clever ways to utilize eggshells:
- Crush very finely and sprinkle around seedlings. Acts as a natural slug and snail deterrent. The sharp grit discomforts soft slug bodies.
- Place crushed shells in the bottom of planting holes when transplanting seedlings. Calcium release helps establish roots.
- Use rinsed shells to start seedlings or propagate cuttings in biodegradable pots. Transplant directly into soil without disturbing roots.
- Scatter around bases of plants prone to blossom end rot like tomatoes, peppers, and squash. Extra calcium reduces this disorder.
- Set eggshell halves in garden beds during spring to attract beneficial beetles and house centipedes that prey on pests.
- Save and grind shells all winter. Apply “eggshell meal” to beds in early spring to fortify soil before planting.
Frequently Asked Questions
Are eggshells safe to compost?
Yes, as long as they are washed, dried, and come only from healthy eggs used for cooking. Do not add raw egg contents, uncooked shells, or eggs from potentially contaminated sources. Salmonella and other pathogens are destroyed during proper hot composting.
Do eggshells acidify soil?
No, eggshells have the opposite effect. They raise pH and provide calcium to counteract soil acidity. However, over-application of crushed shells can make soil too alkaline. Mixing with acidic compost keeps pH balanced.
Can I put eggshells directly in my garden?
It’s better to compost shells first which allows nutrients like calcium to break down into plant-available forms. Raw shells take far longer to breakdown in soil. But lightly crushed shells can be worked into planting holes or seed beds.
Do I need to grind eggshells for compost?
Grinding is not mandatory but optimal for speeding decomposition. The smaller the pieces, the quicker shells integrate into compost. Whole shells take the longest but will still break down eventually. Aim for small fragments or powder.
How many eggshells can I put in my compost?
Limit eggshells to 5-10% of total volume. For home compost with 1 cu ft of materials added each week, 2-3 crushed shells per gallon of compost is sufficient and won’t overwhelm. Scatter shells evenly rather than dense layers.
The Bottom Line
Eggshells are a valuable free resource for improving garden soil through composting. Their calcium and micronutrients amend soil over the long-term. Preparation is simple – just rinse, dry, and crush shells before mixing into compost piles or bins. Given time to break down, eggshells will enrich compost with minerals that boost plant health and productivity when added to gardens. Composting eggshells keeps them cycling through nature rather than wasting in landfills.