The short answer: food scraps, yard waste, and paper — but not meat, dairy, or oils

Compost breaks down organic material into soil-like matter through decomposition. What you put in determines how fast it breaks down, whether it smells, and whether you end up with usable compost or a pile of sludge. The rule is straightforward: add things that rot, avoid things that don't or that attract pests.

The materials that work best fall into two categories. Green materials (nitrogen-rich) include fruit and vegetable scraps, coffee grounds, grass clippings, and plant trimmings. Brown materials (carbon-rich) include dry leaves, shredded paper, cardboard, wood chips, and straw. A working pile needs both — roughly three parts brown to one part green by volume.

Key Takeaways

  • Fruit and vegetable scraps, coffee grounds, and crushed eggshells are safe to add and break down quickly.
  • Meat, fish, dairy, oils, and fats should never go in because they attract rodents and create odor problems.
  • Yard waste like grass clippings and leaves work well, but diseased plants and weeds with seeds can spread problems to your garden.
  • Shredded paper and cardboard are fine; glossy paper, treated wood, and coal ash are not.
  • A balanced pile needs roughly three times as much brown material as green material to decompose without becoming a wet, smelly mess.

What to add: the green materials

Vegetable and fruit scraps are the backbone of most home compost piles. Onion skins, carrot tops, apple cores, banana peels, lettuce scraps, and melon rinds all break down within weeks to a few months. Citrus peels take longer — three to six months — but they do decompose. Cut larger pieces into smaller chunks to speed the process.

Coffee grounds and tea bags (remove the staple and any plastic) add nitrogen and break down fast. Crushed eggshells add calcium and take longer to decompose, but they do not cause problems while they sit. Grass clippings and plant trimmings from your garden are excellent, though fresh grass can mat down and slow air flow — mix it with brown material or let it dry slightly first.

Leaves, straw, and wood chips are the brown materials that balance green scraps. Shredded paper and cardboard (no glossy coating, no colored ink) work too. Sawdust from untreated wood is fine; sawdust from pressure-treated lumber is not. The pile needs this carbon-rich material to avoid becoming a wet, anaerobic sludge.

What to never add: the problem materials

Meat, fish, bones, and any animal products except eggshells attract rats, raccoons, and flies. They also create strong odors as they decompose. Dairy products — milk, cheese, yogurt, butter — do the same. Oils, fats, and grease coat other materials and slow decomposition while drawing pests.

Diseased plants and weeds with mature seeds should not go in unless your pile reaches 140°F or higher, which most home piles do not. The heat kills pathogens and seeds; a cooler pile will spread disease and weeds straight to your garden. Pet waste (dog or cat feces) can harbor parasites harmful to humans and should never be composted at home.

Avoid glossy or colored paper, treated wood, coal ash (wood ash is fine in small amounts), and synthetic materials. Diseased leaves from trees with fungal or bacterial problems can spread those problems when you use the finished compost. When in doubt, leave it out — the pile works fine without it.

How to layer materials for faster breakdown

The fastest compost piles alternate layers: a few inches of brown material, then a layer of green, then brown again. This creates air pockets and mixes nitrogen and carbon throughout. If you have a lot of grass clippings at once, spread them thin or mix them with leaves so they do not pack into a wet mat.

Chop or shred materials before adding them — smaller pieces have more surface area for microbes to work on, so they decompose faster. A pile made of whole leaves and large cardboard pieces can take a year or more; the same materials shredded can be ready in three to six months. If you have a shredder or mulcher, use it.

Keep the pile as moist as a wrung-out sponge. If it is too dry, decomposition slows. If it is too wet, it becomes anaerobic and smells like rotten eggs. Turn the pile every week or two if you want finished compost in two to three months; if you turn it monthly, expect four to six months; if you never turn it, expect a year or more.

Seasonal changes in what you have to add

Spring and summer bring grass clippings and garden trimmings — lots of green material. Fall brings leaves, which are brown. Winter brings little of either unless you live somewhere with year-round growing. Adjust your ratio: in summer, you may need to add extra brown material to balance all the grass; in fall, you may have more brown than you can use.

If you run out of brown material in summer, shred newspaper or cardboard from deliveries, or let grass dry for a day before adding it. If you have a pile of leaves in fall, you can store them in a bin or bag and add them gradually through winter and spring. Composting does not stop in cold weather — it just slows down.

What finished compost looks like

Finished compost is dark brown or black, crumbly, and smells like soil — earthy and neutral. You should not be able to identify the original materials. If you still see whole leaves, cardboard, or food scraps, it is not ready. Sift it through a half-inch screen if you want a fine product for potting or top-dressing; coarser material works fine mixed into garden beds.

Use finished compost to amend garden soil, fill raised beds, top-dress lawns, or pot houseplants. It improves soil structure, adds nutrients slowly, and helps soil hold water. A layer two to four inches thick mixed into the top six inches of garden soil is a good starting point.

Frequently Asked Questions

Can I compost bread, pasta, and cooked food?

Cooked food, bread, and pasta can go in, but they attract pests the same way meat and dairy do. If you have a sealed bin or a very hot pile that you turn regularly, the risk is lower. For an open pile or a lazy bin, skip them. Raw grains and uncooked pasta are safer than cooked versions.

What about pet bedding and manure?

Herbivore manure — from horses, chickens, rabbits, or cows — is excellent compost material and breaks down quickly. Pet bedding made from wood shavings or straw works too. Dog and cat waste should never be composted at home because it can harbor parasites. Avoid manure from animals treated with antibiotics or pesticides.

Can I add weeds and diseased plants?

Weeds without seeds and healthy plants are fine. Weeds with mature seeds and diseased plants should not go in unless your pile reaches 140°F or higher consistently. Most home piles stay cooler, so the seeds and pathogens survive and end up in your garden. When in doubt, throw them in the trash.

How much brown material do I actually need?

Aim for roughly three parts brown to one part green by volume. If your pile smells like ammonia or rotten eggs, add more brown material and turn it. If it is not breaking down and feels dry, add more green material or water. The ratio is a starting point, not a rule — adjust based on how the pile behaves.

What if I only have green scraps and no leaves?

Shred newspaper, cardboard, or paper bags and use them as brown material. Let grass clippings dry for a day before adding them so they do not mat. Sawdust from untreated wood works too. You do not need fallen leaves — any carbon-rich material will balance the nitrogen in your scraps.