The basic rule: browns and greens in layers
A working compost pile needs two types of material in roughly equal amounts: browns (carbon-rich, dry things like leaves and cardboard) and greens (nitrogen-rich, wet things like food scraps and grass clippings). The pile breaks down fastest when you layer them—a few inches of brown, then a few inches of green, then brown again—rather than dumping everything in a heap.
The browns give the pile structure and let air flow through. The greens provide the nitrogen that feeds the microbes doing the actual decomposition. Without both, you either get a soggy, smelly mess (too much green) or a pile that barely changes for years (too much brown). Most home composters find they have plenty of greens from the kitchen and yard, so the real challenge is finding enough browns to balance them.
Key Takeaways
- Browns are dry, carbon-rich materials like leaves, shredded paper, and cardboard; greens are wet, nitrogen-rich materials like food scraps, grass clippings, and plant trimmings.
- Layer browns and greens in roughly equal amounts rather than mixing them together, and keep the pile as moist as a wrung-out sponge.
- Never compost meat, dairy, oils, diseased plants, or pet waste, because they either attract pests, kill beneficial microbes, or spread pathogens to your soil.
- A pile that smells like ammonia has too much green; add more brown material and turn it to let air in.
- Finished compost is dark brown, crumbly, and smells like soil, and usually takes three to six months in an active pile or one to two years in a passive one.
Greens: what to add from your kitchen and yard
Greens are the nitrogen engine of your pile. Fruit and vegetable scraps are the most common: apple cores, banana peels, carrot tops, lettuce leaves, squash ends, coffee grounds, and tea bags (remove the staple first). Grass clippings work well if they have not been treated with herbicide. Fresh plant trimmings from pruning or deadheading add bulk quickly. Crushed eggshells are fine, though they take longer to break down than softer scraps.
Manure from herbivores—horse, cow, chicken, or rabbit—is an excellent green if you have access to it, because it is already rich in nitrogen and contains microbes that speed decomposition. Avoid manure from dogs or cats, which can harbor pathogens that survive composting and contaminate your soil.
Browns: dry materials that give the pile structure
Browns are harder to come by in most households, so save them when you find them. Dry leaves are the gold standard—shred them with a mower or by running over them with a leaf blower to break them into smaller pieces, which decompose faster than whole leaves. Shredded newspaper and cardboard (remove tape and labels) work well. Straw and hay are useful if you have them, though hay may contain weed seeds. Wood chips and sawdust from untreated wood are acceptable, though they take much longer to break down than softer materials.
Paper from your kitchen—paper towels, napkins, uncoated cardboard—counts as brown. Avoid glossy or colored paper, which may contain inks or coatings that do not belong in soil. Shredded office paper is fine. If you heat with wood, ash from a wood stove or fireplace can go in, but use it sparingly—a light dusting only—because too much ash raises the pH and can slow decomposition.
What never goes in: the hard no list
Meat, fish, and bones attract rats and raccoons and take months to break down, even in a hot pile. Dairy products (milk, cheese, yogurt, butter) smell terrible as they decompose and draw pests. Oils and fats create a water-resistant barrier that slows the whole pile. Pet waste from dogs or cats contains pathogens that survive most home composting and can contaminate vegetables you grow later.
Diseased plants and weeds with seeds should not go in unless your pile reaches 140°F or higher—a temperature most backyard piles never hit. If you are unsure whether your pile gets hot enough, leave them out. Treated wood, glossy paper, and synthetic materials do not break down and can introduce toxins. Avoid coal or charcoal ash, which contains substances that harm soil; wood ash in moderation is fine.
Moisture and turning: keeping the pile alive
The pile should feel as moist as a wrung-out sponge—wet enough that a few drops come out if you squeeze a handful, but not so wet that water runs out. If it is too dry, decomposition slows to a crawl. If it is too wet, it becomes anaerobic (oxygen-starved) and smells like ammonia or rotten eggs.
Turning the pile—mixing it with a pitchfork or shovel every week or two—speeds decomposition by introducing oxygen and distributing heat evenly. A turned pile can finish in three to six months. A pile you leave alone will eventually break down, but it takes a year or two. If your pile smells bad, it usually means either too much moisture (let it dry out and turn it) or too much green material (add more brown and turn it).
Size and location matter for faster results
A pile needs to be at least 3 feet by 3 feet by 3 feet to generate enough heat for active decomposition. Smaller piles take longer because they do not retain warmth. Larger piles (up to 5 feet on a side) work well but become harder to turn by hand. If you have limited space, a compost bin or tumbler keeps things contained and makes turning easier.
Location affects how fast things break down. A spot that gets some sun warms the pile and speeds the process. Shade is fine too, but the pile will decompose more slowly. Keep the pile away from your house if possible—not because it is dangerous, but because a large active pile can attract flies or smell strong during hot weather. A location with good drainage prevents water from pooling underneath.
Recognizing finished compost and when to harvest it
Finished compost is dark brown or black, crumbly, and smells like rich soil or forest floor. You should not be able to identify the original materials—no visible food scraps or leaves. If you see whole pieces still in there, the pile needs more time. Finished compost is ready to mix into garden beds, use as mulch, or blend into potting soil.
In an active pile that you turn regularly, you can harvest finished compost from the bottom while the top is still decomposing. In a passive pile, you usually wait until everything looks done, then remove it all at once. Some people keep two piles going—one they are actively adding to and turning, and one they are letting sit—so they always have finished compost available.
Frequently Asked Questions
Can I compost cooked food or leftovers?
Cooked vegetables and grains are fine, but avoid cooked meat, fish, dairy, and oils. They attract pests and smell worse than raw scraps. If you have cooked vegetable scraps, bury them in the center of the pile where it is hottest, and cover them with brown material to keep flies away.
What if my pile smells like ammonia?
That smell means too much nitrogen (too many greens) or not enough oxygen. Add more brown material—shredded leaves or cardboard—and turn the pile thoroughly with a pitchfork. Spread it out a bit to let air in. The smell should fade within a few days.
Do I need to add compost starter or activator?
No. A healthy mix of greens and browns with the right moisture will decompose on its own. Finished compost or garden soil added to a new pile can speed things up slightly by introducing microbes, but it is not necessary. Save your money.
Can I compost sawdust from my workshop?
Yes, if it is from untreated wood only. Sawdust from pressure-treated lumber, plywood, or particle board contains glues or preservatives that should not go in soil. Plain wood shavings or sawdust from solid wood are fine, though they decompose slowly.
How do I know if my pile is too wet?
If water runs out when you squeeze a handful, or if the pile smells sour or like ammonia, it is too wet. Stop adding greens, add more brown material, turn it to introduce air, and let it dry out for a few days. In wet climates, a cover or bin with drainage holes helps.