The Basic Rule: Browns and Greens, Nothing Toxic

You can compost most plant material from your kitchen and yard. The system works by layering greens (nitrogen-rich materials like food scraps and fresh grass clippings) with browns (carbon-rich materials like dry leaves and shredded paper). Bacteria and fungi break these down into dark, crumbly compost you can use in gardens and potted plants.

The things you cannot compost are those that either slow decomposition to a halt, introduce pests or disease, or create odor problems that make your pile unusable. Meat, dairy, oils, diseased plants, and treated wood fall into this category. Everything else is negotiable depending on your pile's size, temperature, and how much time you have.

Key Takeaways

  • Vegetable scraps, fruit peels, coffee grounds, and crushed eggshells are safe greens that speed decomposition and add nutrients.
  • Dry leaves, shredded paper, cardboard, and wood chips are browns that provide structure and allow air flow through the pile.
  • Meat, fish, dairy, oils, and fats attract rats and raccoons and should never go in a backyard pile.
  • Diseased plants, weeds with seeds, and grass treated with herbicides will spread problems rather than break down safely.
  • Layering greens and browns in roughly equal amounts by volume keeps the pile balanced and speeds the breakdown process.

Kitchen Scraps That Belong in Your Pile

Vegetable and fruit scraps are the backbone of most home compost piles. Carrot peels, apple cores, lettuce leaves, onion skins, banana peels, and citrus rinds all break down quickly. Chop larger pieces into smaller chunks so they decompose faster—a whole apple takes longer than apple quarters.

Coffee grounds and tea bags (remove the staple from the bag first) are excellent additions. They are nitrogen-rich and decompose rapidly. Crushed eggshells add calcium and take longer to break down, but they do not harm the pile. Avoid putting in cooked food, grains, bread, or pasta—these attract rodents and can create a sludgy, smelly mess instead of crumbly compost.

Yard Materials That Work Well

Dry leaves are one of the best browns you can use. Shred them with a mower or by hand so they pack less densely and allow air to move through the pile. Grass clippings are a green, but only if they come from a lawn that has not been treated with herbicides or pesticides in the past few months. Fresh clippings mat down easily, so mix them with browns or spread them thinly to prevent compaction.

Wood chips, sawdust from untreated wood, and shredded paper or cardboard are all valuable browns. Avoid glossy or colored paper, which may contain inks or coatings that do not break down safely. Newspaper and plain cardboard are fine. Pine needles and conifer leaves decompose very slowly and can make your pile acidic, so use them sparingly or skip them if you want finished compost within a year.

What Never Goes in a Backyard Pile

Meat, fish, bones, and any animal products attract rats, raccoons, and other pests that will tear apart your pile looking for food. Dairy products like milk, cheese, and yogurt do the same and create foul odors. Oils, butter, grease, and fatty foods break down so slowly that they can make your entire pile anaerobic (oxygen-starved), turning it into a sludgy, smelly mess.

Diseased plants and weeds that have gone to seed will spread those problems into your garden when you use the finished compost. If you have a hot pile that reaches 140°F or higher consistently, it can kill some pathogens and weed seeds, but most backyard piles do not get that hot. When in doubt, throw diseased material in the trash. Treated wood, pressure-treated sawdust, and wood from painted or stained surfaces contain chemicals that do not break down and will contaminate your compost.

Materials That Work but Need Caution

Grass clippings from lawns treated with herbicides or pesticides should not go in your pile for at least a few months after treatment. The chemicals persist and can harm plants you later grow in that compost. If you are unsure whether your lawn has been treated, wait or skip the clippings entirely.

Sawdust and wood shavings from untreated wood are fine, but sawdust from pressure-treated lumber or plywood is not. Leaves from black walnut and eucalyptus trees contain compounds that inhibit plant growth, so compost them separately or use them in small amounts mixed with other materials. Paper with colored inks is usually safe in small amounts, but glossy magazines and coated cardboard are better left out.

How to Layer for Faster Breakdown

The speed of decomposition depends partly on what you put in and partly on how you arrange it. Aim for a ratio of roughly equal volumes of greens and browns—not equal weights, since browns are lighter. Start with a layer of browns (leaves, cardboard, wood chips) about 4 inches thick to create a base that allows air to flow underneath.

Add a layer of greens (vegetable scraps, grass clippings, coffee grounds) about 2 to 4 inches thick, then another layer of browns. Keep alternating. Chop or shred everything you add so pieces are smaller—this increases the surface area bacteria can work on and speeds decomposition by weeks. A pile that is roughly 3 feet by 3 feet by 3 feet will heat up faster than a smaller one, which means it will break down in 2 to 6 months instead of a year or more.

Frequently Asked Questions

Can I put diseased plant material in a hot compost pile?

Only if your pile consistently reaches 140°F or higher for at least two weeks. Most backyard piles do not get that hot. If you are unsure, throw diseased plants in the trash instead. It is not worth spreading disease to your garden.

What about pet waste or cat litter?

Never compost pet waste or cat litter. Dog and cat feces contain pathogens that do not break down in home compost piles and can contaminate vegetables you grow. Commercial pet waste composters exist, but they require special conditions and are not suitable for food gardens.

Can I compost weeds?

Yes, if they have not gone to seed. Once weeds have flowering heads or seed pods, leave them out—your pile will not get hot enough to kill the seeds, and you will spread weeds throughout your garden. Young weeds pulled before flowering are safe to add.

Is it okay to put in moldy food or compost that smells bad?

Mold on food scraps is fine—it is part of the decomposition process. A bad smell usually means the pile is too wet or too densely packed. Add more browns and turn the pile to introduce oxygen. If it smells like ammonia, you have too many greens; add more dry leaves or cardboard.

What about glossy or colored paper?

Plain newspaper and cardboard are safe. Glossy magazines, coated cardboard, and paper with heavy colored inks are better left out because the coatings and inks do not break down reliably. When in doubt, use plain materials instead.