Browns and Greens: The Two Categories That Matter
A working composter needs two types of material: browns (carbon-rich) and greens (nitrogen-rich). The mix matters more than the individual items. Aim for roughly three parts brown to one part green by volume—though experienced composters adjust this by feel as they go. If your pile smells like ammonia or looks slimy, you have too much green. If it barely breaks down after months, you have too much brown.
Browns are dead plant material: dry leaves, shredded paper, cardboard, straw, wood chips, and sawdust. Greens are fresh or wet materials: grass clippings, vegetable scraps, coffee grounds, and plant trimmings. The names can mislead—some browns are technically green in color, and some greens are brown. What matters is whether the material is carbon-heavy (brown) or nitrogen-heavy (green).
Key Takeaways
- Browns (leaves, cardboard, straw, wood chips) should make up about 75 percent of your pile by volume; greens (grass, food scraps, coffee grounds) the remaining 25 percent.
- Shred or chop large items like cardboard, leaves, and woody stems before adding them so they break down faster.
- Never add meat, fish, dairy, oils, diseased plants, or pet waste; these either attract pests or introduce pathogens.
- Grass clippings from lawns treated with herbicide or pesticide should not go in, because those chemicals can persist in finished compost.
- Finished compost is dark, crumbly, and earthy-smelling; it usually takes three months to two years depending on pile size, moisture, and how often you turn it.
Browns: What to Add and How to Prepare Them
Dry leaves are the easiest brown to find in autumn. Shred them with a mower or leaf shredder before adding them—whole leaves mat down and slow decomposition. A pile of shredded leaves alone will break down very slowly without greens mixed in, so layer them with grass clippings or food scraps as you build the pile.
Cardboard and paper work well if they are plain. Remove tape, plastic windows, and glossy coatings. Shred or tear cardboard into pieces smaller than your hand so it breaks down faster. Newspaper, plain paper bags, and unbleached coffee filters are all fine. Avoid colored or heavily printed cardboard, which may contain inks that persist in finished compost.
Straw and hay are useful if you can source them—straw is the hollow stem left after grain is harvested, while hay is dried grass with seeds still in it. Straw is preferable because hay can introduce weed seeds into your compost. Both break down slowly, so chop them into shorter pieces if possible.
Wood chips and sawdust from untreated wood are acceptable, but use them sparingly. They decompose very slowly and can tie up nitrogen as they break down, which means your finished compost may need extra time to mature before using it on vegetables. Sawdust from pressure-treated wood or plywood should never go in.
Greens: Food Scraps, Grass, and Plant Trimmings
Vegetable and fruit scraps are the most common green. Onion skins, carrot peels, apple cores, banana peels, lettuce leaves, and wilted herbs all work. Chop larger pieces into smaller chunks so they break down faster. Citrus peels and onion skins take longer to decompose than softer scraps, but they will eventually break down.
Coffee grounds and tea bags are nitrogen-rich and decompose quickly. Leave grounds in the filter or bag if the bag is paper—both will break down. Remove plastic mesh from some tea bags before composting.
Grass clippings are a reliable green if the lawn has not been treated with herbicide or pesticide within the past few weeks. Fresh clippings heat up a pile quickly and speed decomposition. Spread them out to dry slightly before adding them in large amounts, because a thick layer of wet grass can become matted and anaerobic (lacking oxygen), which slows the process and creates odor.
Plant trimmings from pruning, deadheading, or pulling weeds are fine as long as the plants were healthy. Diseased leaves or stems should go in the trash, not the composter, because many plant diseases survive the composting process and will spread to your garden later.
What Never Goes in the Composter
Meat, fish, and bones attract rats, raccoons, and other pests. They also take a very long time to decompose and can create odor problems. Even in a sealed bin, they are more trouble than they are worth for a home composter.
Dairy products—milk, cheese, yogurt, butter—also attract pests and create odor. Eggs and eggshells are sometimes debated; eggshells alone (rinsed clean) are fine, but eggs themselves should not go in.
Oils and fats slow decomposition and can create a waterproof layer that repels moisture. This includes cooking oil, salad dressing, and fatty meat scraps.
Pet waste from dogs or cats should never be composted at home. It can harbor pathogens that survive the composting process and contaminate vegetables. Horse and chicken manure are different—they are commonly added to compost piles.
Diseased plants, weeds with seeds, and invasive plants like bindweed or Japanese knotweed should go in the trash. Home compost piles often do not get hot enough to kill all seeds or pathogens. If you are unsure whether a plant is diseased, leave it out.
Treated wood, glossy paper, and synthetic materials do not belong in compost. Pressure-treated wood contains arsenic or copper compounds. Glossy magazines and coated cardboard may contain chemicals that persist in finished compost. Plastic, rubber, and synthetic fibers never decompose.
Layering and Moisture: Getting the Balance Right
Build your pile in layers: a few inches of brown, then a layer of green, then brown again. This mixing helps air flow through the pile and keeps the decomposition process moving. If you dump all your greens in one spot and all your browns in another, the pile will work much more slowly.
Moisture is as important as the mix of materials. The pile should feel like a wrung-out sponge—damp but not dripping. If it is too dry, decomposition slows to a crawl. If it is too wet, it becomes anaerobic and smells like rotten eggs or ammonia. In dry weather, water the pile occasionally. In wet weather, you may need to cover it or add more brown material to absorb excess moisture.
Turning and Monitoring Your Pile
A pile that sits undisturbed will eventually become compost, but turning it speeds the process significantly. Turning means mixing the outer edges of the pile into the center, where decomposition is fastest. If you turn the pile every week or two, you can have usable compost in two to three months. If you never turn it, expect six months to two years.
You do not have to turn the pile at all if you are patient. Many people use a straightforward bin and add material to the top, letting the bottom gradually become finished compost while decomposition continues above. This is slower but requires less work.
Finished compost is dark brown or black, crumbly, and smells earthy—not like rotting food. If you can still see the original materials, it is not ready yet. Sift it through a screen or straightforward use it as is; any unfinished pieces will continue to break down in the soil.
Frequently Asked Questions
Can I compost bread, pasta, and cooked food?
Cooked food, bread, and pasta can technically go in a compost pile, but they attract pests just like meat does. If you have a sealed bin and turn the pile frequently, you may get away with it. For an open pile or a bin you do not turn often, it is safer to skip them.
What about glossy or colored paper?
Plain newsprint and uncoated cardboard are safe. Glossy magazines, colored cardboard with heavy printing, and paper with plastic coating should not go in because the inks and coatings may contain chemicals that persist in finished compost.
Can I add weeds to the composter?
Weeds without seeds or roots are fine. Weeds that have already gone to seed or have deep root systems like dandelions should go in the trash instead, because home compost piles often do not get hot enough to kill seeds or root fragments.
Is it okay to add sawdust from my workshop?
Only if it is from untreated wood. Sawdust from plywood, particle board, or pressure-treated lumber contains glues or preservatives that should not go in compost. If you are unsure what the wood was treated with, leave it out.
How do I know if my compost is ready to use?
Finished compost is dark, crumbly, and smells like soil or forest floor. You should not be able to identify the original materials. If it still looks like a pile of leaves and scraps, it needs more time. Even partially finished compost can be worked into garden beds, where it will continue to break down.