Start with the two categories: greens and browns

Compost works because it mixes two types of material. Greens are nitrogen-rich items—mostly food scraps and fresh plant matter. Browns are carbon-rich items—mostly dry leaves, paper, and wood. You need both. Greens alone turn into a wet, smelly mess. Browns alone decompose so slowly you'll think nothing is happening. The balance matters more than the specific items.

A rough target is three parts brown to one part green by volume, though home composters rarely measure precisely and still end up with finished compost. If your pile smells like ammonia or rotten eggs, you have too many greens—add more browns. If it's not heating up or breaking down after months, you probably have too many browns—add more greens or chop everything smaller so it decomposes faster.

Key Takeaways

  • Greens include fruit and vegetable scraps, coffee grounds, grass clippings, and plant trimmings; browns include dry leaves, shredded paper, cardboard, and wood chips.
  • Never compost meat, dairy, oils, diseased plants, or pet waste, as these either attract pests or introduce pathogens that home compost does not get hot enough to kill.
  • Chop or shred larger items before adding them so they break down faster and heat the pile more evenly.
  • Layer greens and browns as you add material, or mix them together; either method works as long as you maintain roughly a 3-to-1 brown-to-green ratio by volume.

Greens: nitrogen-rich materials that heat the pile

Fruit and vegetable scraps are the most common green. Banana peels, apple cores, carrot tops, onion skins, lettuce leaves, and squash rinds all break down in a few weeks to a few months depending on pile temperature and how small you chop them. Coffee grounds and tea bags (remove the staple from tea bags first) are greens too, and they decompose quickly. Eggshells take longer—six months or more—but they add calcium and do eventually break down.

Fresh grass clippings, plant trimmings from your garden, and pulled weeds are greens. So are the leaves you rake off houseplants. Avoid diseased plant material—if a plant had powdery mildew, rust, or blight, leave it out. Home compost piles rarely get hot enough to kill plant diseases, and you'll just spread the problem back to your garden. Weeds with seeds are risky too; if your pile doesn't reach 140°F (60°C) throughout, the seeds may survive and sprout in your finished compost.

Browns: carbon-rich materials that provide structure

Dry leaves are the classic brown. Shredded leaves decompose faster than whole leaves because they have more surface area. If you have a lawn mower, run it over a pile of leaves to shred them, then add them to your compost. Straw and hay are browns (though hay may contain weed seeds, so use straw if you can). Wood chips, sawdust from untreated wood, and small twigs all work. Avoid sawdust from pressure-treated lumber or plywood, which contains chemicals that don't break down.

Paper and cardboard are browns. Shredded newspaper, plain cardboard boxes torn into pieces, paper bags, and paper towels all decompose. Avoid glossy paper, colored inks, and anything with a plastic coating. Cardboard with tape or staples works fine—just remove the tape and staples first. Coconut coir (the fiber from coconut husks) is a brown and a good substitute if you don't have enough leaves. Pine needles and wood ash are browns, though wood ash should be used sparingly because it raises pH and can make compost too alkaline.

What never goes in compost

Meat, fish, bones, and any animal products except eggshells attract rats, raccoons, and flies. Your compost pile won't get hot enough to kill the bacteria in raw meat, so you risk spreading pathogens. Dairy products like milk, cheese, and yogurt also attract pests and can create odor problems. Oils, fats, and grease slow decomposition and create a water-resistant layer that keeps air out.

Pet waste—dog or cat feces—should never go in a home compost pile. It contains pathogens that survive in compost that doesn't reach 160°F (71°C) for extended periods. Municipal composting facilities reach those temperatures; home piles rarely do. Diseased plants, as mentioned above, spread problems to your garden. Weeds with mature seeds may survive and sprout later. Treated wood, glossy paper, and plastic-coated materials don't break down or release chemicals as they decompose.

How to layer and mix your materials

You can layer greens and browns in alternating sections, or you can mix them together as you add them. Both methods work. If you layer, aim for a few inches of brown, then a few inches of green, then brown again. If you mix, chop everything into roughly 1- to 2-inch pieces and stir them together as you add new material. Mixing tends to heat the pile faster because the materials are in closer contact.

Chop or shred everything you can. Whole apple cores take months; chopped apple pieces take weeks. Whole leaves take months; shredded leaves take weeks. A small kitchen knife, garden shears, or a lawn mower all work. If you have a lot of material, a wood chipper or shredder speeds things up, but it's not necessary—patience works too.

Special materials and when to use them

Sawdust from untreated wood is a brown and useful if you have access to it, but use it sparingly—it can compact and slow air flow. Straw (not hay) is a good brown if you can find it. Coconut coir is a brown and works well if you're short on leaves. Shredded paper from a paper shredder is a brown, though it can blow away if your pile is exposed to wind.

Citrus peels, onion skins, and garlic are greens, but use them in moderation. They decompose fine, but large amounts can slow down worms if you're using a worm bin. Bread, pasta, rice, and cooked food scraps are technically compostable greens, but they attract pests more readily than raw vegetables, so many home composters avoid them. If you do add them, bury them deep in the pile under a layer of brown material.

Frequently Asked Questions

Can I compost paper and cardboard?

Yes. Shredded newspaper, plain cardboard, paper bags, and paper towels all decompose. Remove tape and staples first. Avoid glossy paper, colored inks, and anything with a plastic coating like wax-coated takeout containers.

What if I don't have enough leaves for browns?

Use shredded paper, cardboard, straw, wood chips, or coconut coir instead. You can also save leaves in a bag during fall and add them gradually through the year. Grass clippings work as a temporary brown, though they're technically a green—they just have less nitrogen than food scraps.

Do I have to chop everything before adding it?

No, but chopped material decomposes much faster. Whole apple cores take months; chopped pieces take weeks. If you're patient and don't mind waiting, leaving things whole works fine. A lawn mower, kitchen knife, or garden shears all speed up the process.

Can I add cooked food or leftovers?

Technically yes, but they attract pests more readily than raw vegetables. If you do add them, bury them deep in the pile under a thick layer of brown material so they're not exposed to the surface where animals can smell them.

What happens if my compost smells bad?

A rotten-egg or ammonia smell means too many greens and not enough air. Add more browns and turn the pile to mix in oxygen. A sour smell means the pile is too wet. Add dry browns and turn it. A good compost pile should smell earthy, not foul.