Composting eggshells can enrich your compost pile with valuable nutrients like calcium and magnesium. Eggshells are mostly made of calcium carbonate, the same material as seashells and coral. When composted properly, they can be an excellent addition to compost.
However, some precautions should be taken when adding eggshells to compost. Here is a comprehensive guide on the dos and don’ts of composting eggshells.
Can You Compost Eggshells?
Yes, eggshells can and should be composted! Here’s why:
Eggshells Provide Key Nutrients
Eggshells are rich in the following nutrients:
- Calcium – Eggshells are a natural calcium supplement, consisting of over 95% calcium carbonate. Calcium is an essential nutrient for building cell walls in plants.
- Nitrogen – Eggshell membranes contain nitrogen, which is vital for leaf growth and greening. Microbes in compost can break down the membrane and release the nitrogen.
- Phosphorous – Eggshells contain small amounts of phosphorous, which helps plants develop roots, flowers, fruits and seeds.
- Magnesium – Eggshells provide magnesium, which aids in seed germination, enzyme activation and the absorption of phosphorous.
Eggshells Correct Soil pH
Eggshells contain calcium carbonate, a useful pH buffer. When mixed into acidic soils, eggshells can raise pH levels and reduce acidity. Most plants grow best in slightly acidic to neutral soil in the 6.5-7 pH range.
Eggshells Improve Soil Structure
The gritty texture of crushed eggshells helps aerate soil, improve drainage and water retention. Eggshell particles create spaces in the soil that allow roots to spread and grow.
Eggshells Deter Pests
Spreading crushed eggshells around your plants can deter snails and slugs, which don’t like crawling over the sharp, gritty surface. The calcium also disrupts the scent trails of ants.
Eggshells Decompose Slowly
While most compost materials break down within several months, eggshells can take 6 months to 2 years to fully decompose. Their slow release of nutrients provides longer-lasting benefits.
What Not to Compost
While eggshells are compost-friendly, some egg components should not go into home compost piles:
Avoid Raw Eggs and Egg Whites
Raw eggs and egg whites should never be added to compost. They contain proteins that can harbor salmonella and other bacteria that can survive composting temperatures. Always cook or bake eggshells before composting.
Don’t Compost Eggshells from Unknown Sources
It’s best to avoid composting eggshells from restaurants, caterers, or unknown sources, as they may contain residues from raw eggs. Stick to composting clean eggshells from eggs you cracked yourself.
Don’t Overload Your Pile
While eggshells offer benefits, too many can overwhelm a compost system. They break down very slowly, so limit eggshells to 1-2% of your total compost volume.
Don’t Put Whole Eggs In
It may seem convenient to toss in whole raw or cooked eggs, but this can attract pests and rodents. Stick to only composting clean, empty eggshells.
How Long Do Eggshells Take to Compost?
On their own, eggshells can take 6 months to 2 years to fully break down. But when crushed and mixed into an active compost pile, they decompose much faster:
- 6-12 months – Whole eggshells break down slowly. They may take up to a year to decompose when added to an outdoor compost bin.
- 2-4 months – Crushed eggshells mixed into a balanced compost pile typically break down in 2-4 months.
- 4-6 weeks – In a hot, actively managed compost pile, crushed eggshell pieces can decompose in 1-2 months.
- 2-3 weeks – In a high-heat vermicomposting bin, worm activity can reduce eggshells to trace amounts in 2-3 weeks.
Grinding shells into smaller pieces speeds decomposition. Hotter composting temperatures above 130°F also help break down eggshells quickly.
How to Prepare Eggshells for Compost
Proper preparation is key for eggshells to break down efficiently in compost:
Clean and Dry
Rinse eggshells well to remove egg residues. Let shells fully air dry for 1-2 days before composting. Any moisture can slow decomposition.
Crush or Grind
Use a mortar and pestle, rolling pin, or coffee grinder to crush dry shells into smaller pieces. The finer you grind them, the faster they will compost.
Roast (Optional)
Roasting eggshells at 250°F for 10 minutes kills any bacteria and dries them out completely. But this extra step is only necessary if you are concerned about potential pathogens.
Cut Larger Pieces
Break any large eggshell pieces into dime-sized chunks before adding them to compost. Try not to add any pieces larger than 1 inch.
With the right prep, eggshells can rapidly break down from their original form into beneficial nutrients and minerals for your compost.
How to Compost Eggshells
Here are some recommended methods to compost eggshells:
Outdoor Compost Pile
Crush dried eggshells and mix them into your outdoor compost bin. Bury them under 10 inches of other compost materials so they break down faster. Limit eggshells to 1-2% of the total volume. Turn pile occasionally to mix in eggshells.
Vermicomposting / Worm Bins
Add crushed eggshells sparingly to worm compost bins. Worms will help grind them down quickly. Limit to 1 tablespoon per 1 lb of food waste. Don’t overload bin with eggshells.
Compost Tumbler / Spinner
Add a thin layer of crushed eggshells to your compost tumbler and give it a spin regularly. The grinding action will accelerate decomposition. Eggshells should take 1-2 months to disappear.
Bokashi Composting
Sprinkle crushed eggshells into your bokashi bucket. The fermentation process helps soften shells so they break down faster when buried later. Drain liquid when tap is opened.
Trench / Pit Composting
Bury crushed eggshells 6-12 inches deep in outdoor compost trenches or pits. The soil will buffer pH fluctuations from eggshells. Takes 6-12 months to decompose.
Mixing eggshell compost into garden beds or houseplants is an excellent way to recycle nutrients and improve soil quality.
How to Use Eggshells in Gardening & Landscaping
In addition to composting eggshells, you can also use them directly in the garden and landscape in the following ways:
Mix Into Garden Beds
Sprinkle a light dusting of crushed eggshells into planting holes when transplanting seedlings or around established plants. Mix in 1 tbsp per square foot of garden space.
Make DIY Seed Starting Mix
Combine crushed eggshells with coconut coir and compost to create an extra mineral-rich potting mix for starting seeds indoors.
Boost Container Plants
Amend potting soil with 1-2 tablespoons of ground eggshells per gallon of soil. The extra calcium and minerals will boost growth for patio planters and container gardens.
Deter Garden Pests
Surround seedlings with a protective ring of crushed eggshells to block snails and slugs. Dust leaves with eggshell powder to deter aphids.
Level Uneven Ground
Scatter eggshell pieces in muddy or uneven areas. As they decompose, the gritty texture will improve drainage and stabilize soil.
Adjust Soil pH
Work crushed eggshells into overly acidic garden beds to raise pH levels closer to neutral. Use approx 1 pound per 50 sq ft.
Fertilize Houseplants
Recycle used eggshell tea or water by applying it to houseplant soil. The leached calcium will green up leaves.
Troubleshooting Eggshell Composting
Composting eggshells is simple when done properly, but a few issues can arise:
Eggshells Remain Intact
If eggshell pieces are still visible and intact after 6 months in an active compost pile, the shells need to be ground into smaller pieces. Cover them with more “brown” compost materials.
Bad Odor
A rotten egg smell means there is excess moisture slowing decomposition. Dry out the pile by turning it and adding carbon-rich materials like leaves or straw.
Rodents or Pests
Evidence of tunneling or digging means small animals are after the scent of eggshells or egg residues in the compost. Remove any eggshells and thoroughly clean out compost bin. Don’t add eggshells again until the pest issue is resolved.
Calcium Buildup
Too many eggshells can overload soil with calcium. This is rare, but can sometimes hinder the uptake of other nutrients. Test soil pH and adjust as needed by adding organic material.
Slow Decomposition
If eggshell pieces are still present after 1 year of active composting, they likely need to be ground into finer particles. Frequent turning and mixing will also help break them down.
With proper preparation and balance in the compost pile, eggshells can rapidly and safely decompose into a rich source of nutrients. Follow these troubleshooting tips to avoid potential issues.
Frequently Asked Questions
Here are answers to some common questions about adding eggshells to compost:
Can you put eggshells directly in garden soil?
Yes, but it’s best to compost them first. Crushed eggshells mixed into compost will break down over several months before being worked into soil. Directly applying eggshells to garden beds can temporarily impact pH and nutrient balances.
Do you need to wash eggshells before composting?
Washing is recommended to rinse off any egg residue that could attract pests or rodents. Let shells fully dry for 1-2 days before adding to compost pile.
Do eggshells attract animals to compost?
Eggshells alone don’t attract pests, but any bits of egg residue left on shells could lure in animals sniffing out a snack. Thorough washing prevents this problem.
Can eggshells go in worm composting bins?
Yes, in moderation. Crush shells into fine pieces so worms can break them down easily. Limit to 1 tbsp per 1 lb of food waste. Don’t overload bin with too many eggshells.
Do you have to roast eggshells before composting?
No, roasting is an optional step. Boiling water or microwaving for 60 seconds can also sanitize shells and kill bacteria if desired. But crushing and composting is sufficient for most home composters.
How small should crushed eggshells be for compost?
The finer the better for fast decomposition. Crush shells into 0.5 inch or smaller pieces. Coffee grinders make eggshell powder ideal for composting and gardening uses.
Conclusion
When handled properly, eggshells can be a nutritious addition to compost piles and garden soil. Their minerals enrich compost, while their gritty texture improves soil structure.
Follow the recommendations in this guide regarding the right prep, balance, and mixing techniques. With a little practice, eggshells can transform from a kitchen waste into a valuable soil amendment through home composting.