Browns and greens are the two categories that matter
A compost bin works by layering two types of material: browns (carbon-rich) and greens (nitrogen-rich). Browns are dry, dead plant matter—leaves, shredded paper, cardboard, straw. Greens are fresh, moist materials—grass clippings, vegetable scraps, coffee grounds, plant trimmings. The microorganisms that break down your compost need both in roughly equal amounts by volume, though the exact ratio is forgiving. Too many greens and your bin smells like ammonia; too many browns and decomposition slows to a crawl.
The reason this matters is that compost bins are not trash cans. They are controlled environments where specific materials break down into usable soil amendment. What you put in determines whether you end up with dark, crumbly compost in four months or a wet, stinking mess that attracts rats.
Key Takeaways
- Greens (grass, vegetable scraps, coffee grounds) and browns (leaves, cardboard, shredded paper) should go in roughly equal amounts by volume.
- Meat, dairy, oils, and diseased plants should never go in a home compost bin because they attract pests or spread disease to your garden.
- Cooked food, citrus peels, and onions can go in but may slow decomposition or attract animals depending on your bin type and location.
- Shredding or chopping materials before adding them speeds up decomposition by weeks.
- Grass clippings from lawns treated with herbicides or pesticides should not go in unless you know the chemicals have broken down.
Greens that belong in your bin
Greens are nitrogen-rich and break down quickly. Fresh grass clippings are the most common green, but they work best if your lawn has not been treated with herbicides or synthetic pesticides within the past few weeks—those chemicals can persist and end up in your finished compost. If you are unsure, leave the clippings out.
Vegetable and fruit scraps are ideal greens: carrot peels, apple cores, lettuce leaves, broccoli stems, banana peels, melon rinds. Coffee grounds and tea bags (remove the staple from tea bags first) add nitrogen and moisture. Plant trimmings from pruning, deadheading, or pulling weeds all work. Crushed eggshells add calcium and break down slowly, so they are fine to include but will not fully decompose before you use the compost.
Avoid citrus peels, onions, and garlic in large quantities—they decompose slowly and can repel worms if you are using a worm bin. A few peels are harmless; a pile of them will sit there for months. Cooked food scraps (vegetables, grains, pasta) can go in, but they attract rodents more readily than raw scraps, so bury them deep in the center of the pile and only add them if your bin has a find lid.
Browns that belong in your bin
Browns are carbon-rich and decompose slowly, which is why you need them—they create air pockets and balance the moisture that greens bring. Dry leaves are the standard brown and usually free if you rake your own yard. Shredded paper, cardboard (remove tape and labels), and newspaper all work. Straw and hay are excellent if you can source them, though hay may contain weed seeds. Wood chips and sawdust from untreated wood are acceptable, though they take longer to break down than other browns.
Grass clippings that have dried out count as browns. Shredded junk mail, paper bags, and even paper towels and napkins (as long as they have no plastic coating) can go in. The key is that the material should be untreated—no glossy magazine pages, no pressure-treated wood, no cardboard with plastic linings.
What never goes in a home compost bin
Meat, fish, bones, and any animal products except eggshells and coffee grounds should stay out. They attract rats, raccoons, and other pests, and they smell terrible as they decompose. Dairy products (milk, cheese, yogurt, butter) have the same problem. Oils and fats, including salad dressing and cooking oil, create a waterproof layer that blocks air and slows decomposition while attracting pests.
Diseased plants and weeds with mature seeds should not go in unless your compost reaches a temperature above 140°F—most home bins do not. If you have a plant with powdery mildew, blight, or root rot, throw it in the trash. If you have a weed that has gone to seed, the same applies. Diseased compost spread back onto your garden beds will infect next year's plants.
Pet waste (dog or cat feces) and used cat litter belong in the trash. They can harbor pathogens that survive home composting temperatures. Treated wood, glossy paper, and anything with plastic coating should not go in. Charcoal ash from a grill is fine, but coal ash and ash from treated wood are not.
Materials that work but need care
Sawdust and wood chips from untreated wood are safe but decompose slowly—they are better suited to bins you plan to let sit for a year or longer. Pine needles are acidic and take a long time to break down; use them sparingly. Bread, pasta, rice, and other cooked grains can go in, but bury them deep in the center of the pile to avoid attracting rodents.
Glossy or colored paper should not go in, but plain cardboard and newspaper are fine. If you are unsure whether a material is treated or dyed, leave it out. Seaweed and kelp are excellent additions if you live near the coast, but rinse them first to remove excess salt.
How to speed up decomposition with preparation
The smaller the pieces, the faster microorganisms can break them down. Shredding leaves with a mower, chopping vegetable scraps into smaller chunks, and tearing cardboard into strips can cut decomposition time by weeks. A compost shredder or leaf shredder is a one-time investment that pays off if you compost regularly.
Layering matters too. Alternate a layer of greens with a layer of browns, then repeat. This distributes moisture and air throughout the pile. Watering the pile as you build it helps microorganisms get your free guide. If your bin is in a sunny spot, the pile will heat up faster and decompose more quickly than one in shade.
What to do with materials you are unsure about
If you have a material and you are not sure whether it belongs in your bin, the safest approach is to leave it out. Compost bins are forgiving about the right materials but unforgiving about the wrong ones—a single batch of diseased plants or a pile of meat scraps can ruin months of work. When in doubt, throw it in the trash.
If you are building a new bin and want to avoid mistakes, start with just grass clippings and leaves for your first batch. Once you see what finished compost looks like and how long it takes, you can experiment with other materials. Most home composters find that they settle into a routine of adding vegetable scraps, grass clippings, and leaves, and that combination alone produces excellent compost.
Frequently Asked Questions
Can I put bread and pasta in my compost bin?
Yes, but bury them deep in the center of the pile. Cooked grains attract rodents more readily than raw vegetable scraps, so a find lid and burying the material helps reduce the risk. If you live in an area with a lot of rats or raccoons, it is safer to skip them.
What if I accidentally put meat or dairy in my bin?
Remove it if you can. If it is already mixed in, add extra browns to the pile and turn it more frequently to speed decomposition and reduce odor. In the future, keep a small container in your kitchen for meat and dairy scraps and take it to the trash separately.
Can I compost glossy or colored paper?
No. Glossy paper contains coatings that do not break down in a home compost bin, and some colored inks contain heavy metals. Stick to plain cardboard, newspaper, and uncoated paper.
Do I need to remove labels and tape from cardboard before composting it?
Yes. Labels and tape are usually plastic or plastic-coated, so they will not decompose. Tear them off and compost only the plain cardboard.
Is it safe to compost weeds from my garden?
Only if the weeds have not gone to seed. If they have seed heads, throw them in the trash—your compost bin probably will not get hot enough to kill the seeds, and you will spread them back onto your garden beds when you use the finished compost.