The Basic Rule: Browns and Greens in Balance

A working compost bin needs two types of material: greens (nitrogen-rich, wet things) and browns (carbon-rich, dry things). The microbes that break down your waste need both to thrive. A good starting ratio is roughly three parts brown to one part green by volume, though you will adjust this as you go. If your pile smells like ammonia or looks slimy, you have too many greens. If it barely breaks down and stays cold, you have too many browns.

The names are misleading—not all greens are actually green, and not all browns are brown. What matters is the chemical makeup, not the color. Grass clippings are green (nitrogen-rich) even though they are green-colored. Shredded newspaper is brown (carbon-rich) even though it is white. Once you know what category something falls into, you know whether to add it.

Key Takeaways

  • Greens include fresh grass clippings, vegetable scraps, coffee grounds, and plant trimmings; browns include dry leaves, shredded paper, cardboard, and wood chips.
  • Never add meat, dairy, oils, pet waste, diseased plants, or weeds with seeds, because they either attract pests or kill the microbes you need.
  • Chop or shred larger items before adding them so they break down faster and do not create air pockets that slow decomposition.
  • Layer greens and browns as you add material, or mix them together every week or two to keep the pile balanced and working.
  • If your bin smells bad or attracts animals, you likely have too many greens or the wrong kind of material—adjust what you add next.

What Goes In: Greens (Nitrogen-Rich Materials)

Greens are the fresh, wet materials that feed the microbes doing the work. Vegetable and fruit scraps are the most common: carrot peels, apple cores, lettuce leaves, onion skins, banana peels, and coffee grounds all break down quickly. Grass clippings work well if they have not been treated with herbicide. Fresh plant trimmings—stems and leaves from pruning—count as green. Tea bags (remove the staple first) and crushed eggshells also belong here.

Manure from herbivores is green material: horse, cow, rabbit, and chicken manure all add nitrogen. Avoid dog and cat waste—they carry pathogens that compost temperatures do not reliably kill. Seaweed and kelp are excellent greens if you have access to them. The key is that these materials are moist and will break down relatively fast, usually within weeks to a few months depending on how finely chopped they are.

What Goes In: Browns (Carbon-Rich Materials)

Browns are the dry, woody materials that provide structure and carbon. Dry leaves are the most obvious choice—rake them up in fall and shred them with a mower before adding so they do not mat down and trap air. Shredded newspaper, cardboard (remove tape and labels), and paper bags all work. Wood chips, sawdust from untreated wood, and straw (not hay, which has seeds) are browns. Shredded office paper, junk mail, and paper towels are fine too.

The reason to shred or chop browns is that whole leaves and large cardboard pieces create air gaps that slow decomposition. A mower, leaf shredder, or even running over leaves with a lawn mower in a pile works. Cardboard breaks down faster if you tear it into strips rather than leaving it in large sheets. The finer the pieces, the faster they decompose and the easier they are to mix with greens.

What Never Goes In: The Prohibited List

Meat, fish, bones, and any animal products besides manure and eggshells attract rats, raccoons, and flies. They also take much longer to break down and can create odor problems. Dairy products—milk, cheese, butter, yogurt—do the same. Oils and fats, including cooking oil and grease, slow decomposition and create a waterproof layer that blocks air flow.

Do not add diseased plants or weeds with mature seeds. Compost piles do not reliably reach temperatures high enough to kill plant diseases or seeds unless you are actively managing temperature (turning frequently and keeping the pile large). If you add a tomato plant with late blight or a dandelion gone to seed, you will spread the problem when you use the finished compost. Pet waste, including cat litter, carries parasites and pathogens. Treated wood, glossy paper, and anything with synthetic coatings do not belong either—they contain chemicals that do not break down or that harm soil.

How to Layer and Mix for Faster Breakdown

The fastest way to compost is to layer as you add material: a few inches of brown, then a few inches of green, then brown again. This distributes the greens throughout the pile so microbes have access to nitrogen everywhere, not just in pockets. If you are adding to your bin gradually over weeks, aim to add roughly equal volumes of brown and green, adjusting if the pile starts to smell or look wrong.

If you want faster results, turn the pile every week or two—mix the outside material toward the center and the center material toward the outside. This adds oxygen, which speeds up the microbes' work. A pile that is turned regularly can produce finished compost in two to three months. A pile left alone takes six months to a year. Either way works; turning is just faster.

Adjusting What You Add Based on What You See

Your pile will tell you if the balance is wrong. A strong ammonia smell means too many greens—add more browns and turn the pile to add air. A slimy, wet appearance also signals too many greens; let it dry out a bit and mix in shredded leaves or cardboard. If the pile is cold and barely breaking down after several weeks, you have too many browns—add more vegetable scraps or grass clippings and turn it.

Fruit flies or gnats usually mean you added fruit or vegetable scraps without covering them with brown material. Bury fresh scraps under a layer of leaves or shredded paper so they are not exposed to air. Rodents mean you added meat, dairy, or oils. Stop adding those materials and cover the pile with a lid or hardware cloth if you have one. These adjustments are normal—composting is not a fixed formula, and every pile is different depending on what you have available and your climate.

Special Materials: Leaves, Grass, and Paper

Fall leaves are the easiest brown material to find in large quantities. Shred them with a mower before adding—whole leaves pack down and exclude air, which slows decomposition. A pile of shredded leaves alone will eventually compost, but it takes longer without greens mixed in. If you have a lot of leaves, you can make a separate leaf pile and use it as your brown supply throughout the year.

Grass clippings are excellent greens, but only if they have not been treated with herbicide or fungicide. Clippings from a lawn that was recently sprayed will kill the microbes in your compost. If you are unsure, let the grass dry out first—dried grass is less likely to mat down and is easier to mix in. Shredded paper and cardboard are free and plentiful if you have an office or receive mail. Avoid glossy paper, colored inks that contain heavy metals, and anything with a plastic coating. Plain newsprint, kraft paper, and cardboard are safe.

Frequently Asked Questions

Can I add citrus peels and onions to my compost?

Yes, both are fine. Citrus peels take longer to break down than softer scraps, so chop them into smaller pieces. Onion skins and layers are greens and decompose quickly. The only reason to limit citrus is if you add so much that the pile becomes too acidic, but that is rare in a home bin.

What about bread, pasta, and cooked food?

Avoid cooked food, bread, and pasta. They attract rodents and can create odor problems. Uncooked grains and legumes are technically compostable but attract pests, so it is safer to skip them. Stick to raw vegetable and fruit scraps.

Can I compost glossy magazine pages or colored paper?

No. Glossy paper has a plastic coating that does not break down. Colored inks in magazines and junk mail can contain heavy metals. Stick to plain newsprint, kraft paper, and cardboard without coatings or tape.

How do I know when my compost is ready to use?

Finished compost is dark brown, crumbly, and smells earthy—not like ammonia or rotting food. You should not be able to identify the original materials. If you see whole leaves or cardboard pieces, it is not ready yet. Let it sit longer or turn it more frequently to speed things up.

Do I need to add water to my compost bin?

Usually not, because greens provide moisture. If your pile is very dry and not breaking down, water it lightly until it feels like a wrung-out sponge. Too much water excludes air and creates odor, so add water sparingly and only if the pile looks dry.