What Goes Into a Compost Bin
A compost bin breaks down organic material into soil you can use in gardens and planters. Most bins accept two broad categories: green materials (nitrogen-rich, wet items) and brown materials (carbon-rich, dry items). The bin works best when you balance both — roughly three parts brown to one part green by volume.
Green materials include fruit and vegetable scraps, grass clippings, plant trimmings, coffee grounds and tea bags, and fresh manure from herbivores. Brown materials include dry leaves, shredded paper and cardboard, wood chips, straw, and sawdust. The microorganisms in the bin consume both types and generate heat as they work, which speeds decomposition.
What you put in determines how fast the pile breaks down and whether the finished compost is safe to use. A bin that receives only kitchen scraps will decompose slowly and may smell. A bin that receives the right mix of materials will be ready in weeks to months, depending on temperature and how often you turn it.
Key Takeaways
- Green materials (fruit scraps, grass, coffee grounds) and brown materials (leaves, cardboard, wood chips) should be mixed at roughly a 1:3 ratio by volume for fastest decomposition.
- Meat, dairy, oils, and diseased plants should never go in a home compost bin because they attract pests, create odor, or spread plant disease.
- Glossy or coated paper, pet waste, and treated wood will not break down properly and can contaminate the finished compost.
- A balanced bin with the right moisture and air flow will produce usable compost in two to six months, depending on climate and turning frequency.
- Shredding or chopping materials before adding them speeds decomposition by increasing surface area for microorganisms to work on.
Green Materials That Belong in the Bin
Green materials are wet, nitrogen-rich items that heat up the pile and feed the microorganisms doing the work. Fruit and vegetable scraps are the most common: apple cores, banana peels, carrot tops, lettuce, broccoli stems, onion skins, and potato peels all break down quickly. Citrus peels and onions take longer but still decompose. Avoid avocado pits and shells — they take months and can harbor mold.
Grass clippings, plant trimmings, and garden waste are green materials if they are fresh and moist. Grass clippings should be added in thin layers (no more than two inches at a time) so they do not mat down and block air flow. Pulled weeds are fine as long as they have not gone to seed. Deadheaded flowers, spent vegetable plants, and pruned branches all work.
Coffee grounds, tea bags, and crushed eggshells are green materials. Remove the metal staple from tea bags first. Herbivore manure — from horses, rabbits, chickens, or cows — is nitrogen-rich and speeds decomposition, but manure from meat-eating animals should not go in a home bin.
Brown Materials That Belong in the Bin
Brown materials are dry, carbon-rich items that provide structure and air pockets. Dry leaves are the most accessible: rake them in fall and store them in bags to add throughout the year. Shredded paper and cardboard (without glossy coating or colored ink) break down readily. Newspaper, junk mail, and plain cardboard boxes all work. Tear or shred them into pieces so they decompose faster.
Wood chips, sawdust, and straw add bulk and air space. Sawdust from untreated wood is safe; sawdust from pressure-treated lumber is not. Straw (not hay, which contains seeds) works well. Pine needles and wood ash from a fireplace can go in, though wood ash should be no more than 5 percent of the pile by volume because it raises pH.
Shredded junk mail, paper bags, and cardboard from packaging are brown materials if they have no plastic coating or colored inks. Plain kraft paper and kraft paper bags work. Avoid glossy magazines, coated cardboard, and paper with colored printing, as the inks and coatings do not break down.
What Never Goes in a Home Compost Bin
Meat, fish, bones, and any animal products except manure should never go in a home bin. They attract rats, raccoons, and other pests, and they create strong odors as they decompose. Dairy products — milk, cheese, butter, yogurt — do the same. Oils, grease, and fatty foods break down very slowly and can create a waterlogged, anaerobic layer that smells.
Pet waste (dog or cat feces) contains pathogens that survive home composting temperatures and can contaminate the finished compost. Human waste should not go in either. Diseased plants — those with fungal infections, blight, or mildew — will spread disease to whatever you use the compost on. Weeds that have already set seed will germinate in the finished compost.
Treated wood, pressure-treated lumber, and plywood contain chemicals that do not break down and will contaminate the compost. Glossy or coated paper, plastic-lined cardboard, and paper with heavy colored inks should stay out. Synthetic materials like plastic, rubber, and metal do not decompose in a home bin.
How to Prepare Materials Before Adding Them
Chopping or shredding materials before they go in the bin speeds decomposition significantly. Smaller pieces have more surface area for microorganisms to work on. Fruit and vegetable scraps can be left whole or cut into quarters — smaller is faster. Leaves can be shredded with a lawn mower or leaf shredder, or torn by hand. Cardboard should be torn or shredded into strips no wider than two inches.
Grass clippings should be spread thin so they do not clump. If you have a large amount, let them dry for a day or two before adding them, or mix them thoroughly with brown material as you layer. Woody branches thicker than a pencil should be chipped or cut into small pieces; thin twigs can go in whole.
Do not add materials that are wet or moldy from storage. If leaves or cardboard have gotten damp, let them dry before adding them. A damp pile can become anaerobic and smell like rotten eggs.
Balancing Your Bin for Faster Decomposition
The speed at which your bin produces finished compost depends on the ratio of green to brown materials, moisture, temperature, and how often you turn it. A ratio of roughly three parts brown to one part green by volume is the target. This means if you add a bucket of grass clippings, add three buckets of leaves or shredded cardboard.
Moisture should feel like a wrung-out sponge — damp but not dripping. If the pile is too dry, decomposition slows. If it is too wet, it becomes anaerobic and smells. In dry climates, water the pile when you add materials. In wet climates, cover the top to shed excess rain.
Temperature matters: decomposition happens fastest between 130 and 150 degrees Fahrenheit, which occurs naturally in a large, well-balanced pile. Turning the pile every week or two speeds the process by introducing oxygen and mixing materials. A bin that is turned regularly can produce finished compost in two to three months. A bin that is left alone may take six months to a year.
Signs Your Compost Is Ready to Use
Finished compost looks like dark brown soil, smells earthy, and crumbles in your hand. You should not be able to identify the original materials — everything should be broken down. If you still see recognizable food scraps or leaves, the pile needs more time.
If your bin has a removable bottom or door, you can harvest finished compost from the bottom while the top is still decomposing. This lets you use the compost without waiting for the entire pile to finish. Sift the finished compost through a screen to remove any large pieces, and return those pieces to the bin to break down further.
Frequently Asked Questions
Can I put bread, pasta, and cooked food in the compost?
Bread, pasta, rice, and cooked vegetables can go in, but they attract pests and smell if not buried deep in the pile. Add them sparingly and cover them with brown material when ready. Cooked food with oil, butter, or meat should not go in.
What about paper towels and napkins?
Plain paper towels and napkins break down readily and count as brown material. Avoid those with heavy printing or coating. Paper towels used to clean up meat or dairy should not go in because they carry those materials into the bin.
Can I compost pine needles and conifer branches?
Yes, but slowly. Pine needles and conifer branches are acidic and break down more slowly than other brown materials. They work fine mixed with other materials, but a pile made mostly of pine needles will take longer to finish.
Is it okay to add weeds to the bin?
Weeds without seeds are fine. Weeds that have already flowered or set seed will germinate in the finished compost and spread weeds wherever you use it. Pull weeds before they flower, or let them dry completely in the sun for several days before adding them.
What if my compost smells bad?
A rotten-egg or ammonia smell means the pile is too wet or has too much green material and not enough oxygen. Turn it thoroughly, add brown material, and let it dry out. A sour smell usually means the pile is anaerobic. Turning it and adding air will fix it within a few days.