Browns and Greens: The Two Categories That Matter
A working compost pile needs two types of material: browns (carbon-rich) and greens (nitrogen-rich). Browns are dry, dead plant matter—leaves, straw, shredded paper, cardboard. Greens are fresh or moist materials—grass clippings, vegetable scraps, coffee grounds, plant trimmings. The pile breaks down fastest when you layer them roughly equally by volume, though exact ratios are forgiving. Too many browns and decomposition slows; too many greens and the pile becomes wet and smelly.
The reason this split matters is chemistry. Microorganisms that eat dead plant matter need both carbon and nitrogen to reproduce and do their work. A pile with only one type will sit dormant. Most home gardeners find success by adding browns whenever they add greens—a layer of leaves over kitchen scraps, shredded paper over grass clippings—rather than worrying about precise measurement.
Key Takeaways
- Vegetable and fruit scraps, coffee grounds, and crushed eggshells are safe greens; meat, dairy, oils, and pet waste belong nowhere near compost.
- Leaves, straw, shredded paper, and cardboard are reliable browns that speed decomposition and prevent odor.
- Diseased plants, weeds with seeds, and treated wood should not go in because they survive the pile and spread problems to your garden.
- Grass clippings work as greens only if the lawn was not treated with herbicide or fungicide within the past few weeks.
- A balanced pile smells earthy; if it smells like ammonia or rotten eggs, add more browns when ready.
Kitchen Scraps That Belong in the Pile
Vegetable and fruit scraps are the easiest greens to add. Carrot peels, apple cores, lettuce leaves, onion skins, banana peels, melon rinds, and wilted herbs all break down readily. Bury them under a layer of browns so they do not attract flies or raccoons. Coffee grounds and tea bags (remove the staple from tea bags first) add nitrogen and break down quickly. Crushed eggshells take longer to decompose but add calcium and do not create odor problems.
Avoid anything that came from an animal. Meat, fish, bones, dairy products, oils, and fats do not belong in a home pile. They attract rats and other pests, create strong odors as they rot, and can harbor pathogens. Cooked food scraps should also stay out—cooking can make some materials harder to break down, and the smell draws animals. If you have a lot of food waste and want to compost it, consider a separate hot-composting system or a commercial composting program in your area that accepts these materials.
Yard Waste and Paper Materials
Dry leaves are the gold standard brown. Shred them with a mower or leaf shredder if you have one—smaller pieces decompose faster—but whole leaves work too. Straw (not hay, which contains seeds) is excellent. Shredded newspaper and cardboard are reliable browns; remove tape and glossy labels first. Plain paper from your office, junk mail, and paper bags all work. Avoid glossy magazines, colored inks that contain heavy metals, and paper with plastic coating.
Grass clippings are a useful green, but timing matters. If your lawn was treated with herbicide or fungicide, wait at least two to three weeks before adding clippings to compost—the chemicals can kill the microorganisms that do the decomposing. Clippings from an untreated lawn are fine. Wood chips and sawdust are browns, but use them sparingly; they decompose very slowly and can tie up nitrogen as they break down. Never add treated wood, plywood, or wood from pressure-treated lumber—the chemicals persist in compost and end up in your garden soil.
What Not to Compost and Why
Diseased plants and weeds with mature seeds should not go in a home pile. Most backyard comosts do not reach the temperature (above 140°F for several days) needed to kill pathogens or viable seeds. If you add a tomato plant with late blight or a dandelion gone to seed, you are spreading the problem directly to your garden when you use the finished compost. Diseased material is better burned or thrown away; weeds can go in only if you are certain they have not flowered yet.
Pet waste—dog or cat feces—should never be composted at home. It can harbor parasites and pathogens that survive the pile and contaminate vegetables. Synthetic materials like plastic, rubber, and treated fabrics do not break down. Glossy or colored paper, coal ash, and charcoal briquette ash also stay out. Wood ash from a fireplace or wood stove can go in, but use it sparingly (no more than a thin layer every few months) because it raises pH and can make the pile too alkaline. Sawdust from pressure-treated wood, plywood, or composite materials is off-limits.
How to Layer for Faster Breakdown
The simplest method is to alternate layers: a few inches of browns, then a few inches of greens, then browns again. Water each layer lightly as you build so the pile stays moist but not soggy—like a wrung-out sponge. Turn the pile every week or two with a fork or shovel to speed decomposition; turning mixes materials, introduces oxygen, and can cut the time to finished compost from several months to six to eight weeks. If you do not turn it, expect finished compost in six months to a year.
Keep the pile at least 3 feet by 3 feet if you can; smaller piles do not retain heat as well and decompose more slowly. If the pile smells like ammonia or rotten eggs, it has too much nitrogen (too many greens). Add a thick layer of browns and turn it. If it is not heating up or breaking down, it probably needs more greens or more moisture. A working pile should feel warm in the center and smell earthy, not foul.
Unusual Materials You Can Compost
Hair and fur from brushing pets or your own head are fine—they are protein and break down eventually. Wool scraps, cotton fabric, and natural fiber rope all decompose. Seaweed and kelp are excellent greens if you live near the coast; rinse them first to remove excess salt. Feathers, nail clippings, and human hair all work. Wood ash from a fireplace (not charcoal) can go in moderation. Shredded junk mail, paper towels, and paper napkins are browns. Aquarium water (if you have a freshwater tank) is a useful green because it contains nitrogen from fish waste.
Sawdust from untreated wood is a brown, though it decomposes slowly. Pine needles are acidic and break down very slowly, so use them sparingly if your goal is to finish compost quickly. Lint from a clothes dryer made of natural fibers (cotton, wool) works as a brown. Avoid lint from synthetic fabrics. Spent mushroom compost and used potting soil can go in if they do not contain perlite or other synthetic amendments. When in doubt, remember the rule: if it came from a plant or animal (not including meat or dairy) and was not treated with chemicals, it probably belongs in the pile.
Frequently Asked Questions
Can I put citrus peels and onions in compost?
Yes, citrus peels and onion skins are safe. They break down slowly because of their tough outer layer, but they do not harm the pile. Bury them under browns so they do not attract pests. Some gardeners avoid large quantities of citrus because the acidity can slow decomposition slightly, but a few peels per week are fine.
What if I accidentally put meat or dairy in the pile?
Remove it if you notice it soon. If it is already buried and you did not see it, cover it with a thick layer of browns and turn the pile. The smell and pests may still be a problem, but burying it deeper and adding browns limits the damage. Going forward, keep a separate container for meat and dairy scraps.
Can I compost glossy paper or cardboard with printing?
Plain cardboard and newspaper are fine. Glossy paper, magazines with color photos, and cardboard with plastic coating should stay out because the inks and coatings can contain heavy metals or chemicals that end up in your finished compost and garden soil.
How do I know if my pile is too wet?
Squeeze a handful of compost. If water drips out, it is too wet. Add more browns and turn the pile to introduce air. If it feels like a wrung-out sponge with no water dripping, the moisture is right. A wet pile smells bad and decomposes slowly.
Can I put weeds in compost if I pull them before they flower?
Yes, if you are certain they have not flowered or set seed. Once a weed has flowered, seeds may be present even if you cannot see them. When in doubt, throw it away or burn it. The risk of spreading weeds through your garden is not worth the small amount of compost you save.