A Guide to Composting Coffee Grounds and Eggshells
If you’re wondering whether you can compost both coffee grounds and eggshells, the answer is an affirmative yes - they're two of the best additions to any compost pile or bin. Coffee grounds add nitrogen to kickstart decomposition, while eggshells provide calcium that strengthens plant cell walls and prevents issues like blossom end rot in tomatoes. Together, they create balanced, nutrient-rich compost without additives. I've been tossing them in for years, and my garden soil has been thriving since.
Why Coffee Grounds
Used coffee grounds are a nitrogen-rich "green" material that heats up your compost and feeds microbes. They're nearly pH-neutral (around 6.5), so the myth about them acidifying soil is mostly untrue. I collect mine daily and one pot's worth speeds up breakdown in my compost bin. They also deter slugs and suppress some fungal diseases naturally. Sprinkling grounds around my hostas during summers kept the slime trails away better than any store-bought bait.
Eggshells: Slow-Release Calcium Boost
Crushed eggshells break down slowly to release calcium carbonate, which sweetens acidic soil and builds strong plants. Rinse them first to avoid attracting pests, then crush them. I bake mine dry and toss in a blender for faster breakdown. They're especially great for tomatoes, peppers, and squash. One year my tomatoes had zero end rot after I started adding in egg shells; while the fruits were firmer and more abundant.
Adding Them to Your Compost
Balance is the key for a good compost: mix coffee grounds (greens) with eggshells and browns like leaves or cardboard. In a traditional bin, layer them in; and they will decompose in months. For faster results indoors, use a countertop unit like the kitchen composter, as it handles grounds and shells effortlessly with odor control, and turns waste into nutrient-rich material in just hours. I add my morning coffee and breakfast shells daily so there’s no mess and no hassle.
Common Issues and Quick Fixes
Don't overload on coffee grounds alone as they can mat and slow airflow; always mix them with browns instead. Eggshells will take forever to decompose if not crushed, so smash them into powder for quicker results. If your pile smells, add more browns. With the kitchen composter's app guidance, balancing is easy and convenient.
Real Garden Wins
My garden plants and raised beds have continued to thrive on a combination of richer soil, fewer pests, and healthier plants. The addition of compost with coffee grounds and shells have definitely contributed to improved harvests in previous seasons. Start small - save your coffee and eggs for the next compost batch, and watch your garden transform. It's free, easy, and pretty satisfying too.
