Browns and Greens: The Two Categories That Matter

Compost works because it mixes 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, wet materials — grass clippings, vegetable scraps, coffee grounds, plant trimmings. A working pile needs both. Too many browns and decomposition slows to a crawl. Too many greens and the pile becomes a wet, smelly mess.

The ratio that works for most home composters is roughly three parts brown to one part green by volume, though you do not need to measure exactly. If your pile smells like ammonia or looks slimy, add more browns. If it is not breaking down after months, add more greens and turn it more often.

Layering matters more than ratio. Alternate a layer of greens with a layer of browns as you add material. This creates air pockets and keeps the pile from compacting into a solid block. A 4-inch layer of grass clippings, then a 12-inch layer of shredded leaves, then kitchen scraps, then more leaves — this pattern works better than dumping everything in at once.

Key Takeaways

  • Browns (leaves, cardboard, straw) and greens (grass, food scraps, coffee grounds) must both go in; aim for roughly three parts brown to one part green.
  • Layer materials as you add them rather than mixing everything together, which helps air flow through the pile.
  • Meat, dairy, oils, diseased plants, and pet waste do not belong in home compost because they attract pests, spread disease, or take too long to break down.
  • Shredded or torn cardboard and paper break down faster than whole sheets; avoid glossy, colored, or treated paper.
  • Grass clippings from lawns treated with herbicide or pesticide should not go in unless you know the chemicals used.

Greens You Can Add Without Worry

Vegetable and fruit scraps are the easiest greens to start with: carrot peels, apple cores, lettuce leaves, onion skins, melon rinds, tomato stems. Bury them under a layer of browns so they do not attract flies. Citrus peels take longer to break down than softer scraps, but they do break down. Avocado pits and banana peels are fine — they just take months.

Coffee grounds and tea bags (remove the staple from tea bags) are nitrogen-rich and decompose quickly. Crushed eggshells add calcium and break down slowly, which is fine; they do not slow the overall pile. Fresh grass clippings are excellent greens, but only if they come from a lawn that has not been treated with herbicide or pesticide in the past few weeks. Clippings from a recently sprayed lawn will kill the microbes doing the decomposing.

Plant trimmings — spent tomato plants, pulled weeds, deadheaded flowers — all go in as long as they are not diseased. If a plant had powdery mildew, early blight, or another fungal disease, leave it out; home compost piles do not get hot enough to kill those spores, and you will spread the disease back to your garden next year.

Browns That Work Best

Dry leaves are the gold standard brown. Shred them with a mower or by running over them with a lawn mower before adding them; whole leaves mat down and decompose slowly. If you do not have leaves, straw (not hay, which contains seeds) works well. Shredded newspaper and cardboard are also excellent — tear or shred them into strips so they do not form a solid layer that water cannot penetrate.

Wood chips and sawdust are browns, but use them sparingly. They take a long time to break down, and sawdust from treated wood (pressure-treated lumber, plywood with glue) should not go in at all. Sawdust from untreated wood is fine in small amounts mixed with other materials. Pine needles and conifer needles are acidic and break down slowly; use them if you have them, but do not rely on them as your main brown source.

Paper and cardboard must be free of glossy coating, colored ink, and plastic tape. Plain brown cardboard boxes, shredded newspaper, and plain paper are fine. Avoid magazines, junk mail with colored printing, and anything laminated. Cardboard with tape still attached will not break down and will jam a shredder.

What Never Goes in Compost

Meat, fish, bones, and any animal product except eggshells attract rats, raccoons, and flies. Dairy — milk, cheese, yogurt, butter — also attracts pests and can create odor problems. Oils and fats (including salad dressing and cooking oil) coat the pile and slow decomposition while drawing rodents. Diseased plants spread infection to your garden when you use the finished compost.

Pet waste — dog or cat feces — should never go in. It contains pathogens that home compost does not get hot enough to kill. Diseased plant material, as mentioned above, includes anything with visible fungal growth, spots, or wilting from disease. Weeds that have gone to seed will survive composting and spread when you use the finished product. If you are unsure whether a weed has set seed, leave it out.

Treated wood, pressure-treated sawdust, and wood from painted or stained furniture contain chemicals that do not break down and will contaminate your compost. Glossy or colored paper, magazines, and cardboard with plastic coating do not decompose properly. Synthetic materials — plastic, rubber, treated fabric — have no place in compost.

Grass Clippings and Yard Waste: When to Use Them

Fresh grass clippings are excellent greens, but only from untreated lawns. If your lawn has been treated with a broadleaf herbicide (like 2,4-D, used to kill dandelions) or an insecticide, do not add clippings for at least two weeks after process. Better yet, ask your lawn care company or check the label on whatever you applied — some chemicals persist longer than others.

If you bag grass clippings and store them before adding them to compost, they will heat up and begin decomposing in the bag. This is fine; they will still work in your pile. If clippings have begun to smell like silage (sour, fermented), they are still usable — just mix them in with plenty of browns to balance the moisture.

Leaves from diseased trees — like those with anthracnose, apple scab, or other fungal infections — should not go in. Healthy leaves from any tree are fine. Oak leaves are acidic and take longer to break down, but they work. Walnut leaves contain a chemical called juglone that can inhibit plant growth; compost them separately if you have a lot, or mix them with other leaves so they are diluted.

Paper, Cardboard, and Wood Products

Shredded newspaper is one of the easiest browns to use. Avoid the glossy inserts that come with newspapers; stick to the black-and-white text pages. Cardboard boxes work well — flatten them, tear them into strips, and layer them with greens. Wet cardboard before adding it so it does not repel water and create a dry pocket in your pile.

Paper towels and napkins are fine if they are not bleached white (which means they have been treated with chlorine). Brown paper towels and unbleached napkins work. Avoid paper with food residue that includes meat, dairy, or oil — those attract pests. Plain food-stained paper is fine.

Cardboard with plastic tape, plastic windows, or plastic coating should not go in. Wax-coated cardboard (like some takeout containers) does not break down. If you are unsure whether a cardboard box is coated, tear it — if it feels waxy or plastic-like, leave it out.

Troubleshooting: When Your Pile Is Not Working

If your compost smells like ammonia or rotten eggs, you have too much green material and not enough air. Add more browns, break up any compacted layers, and turn the pile if you can. If it smells like that for weeks despite adding browns, the pile may be too wet; add more dry material and turn it more often to introduce oxygen.

If your pile is not heating up and breaking down after two months, it either lacks nitrogen (add more greens like grass or food scraps) or lacks air (turn it more often or add bulky browns like shredded leaves to create air pockets). A pile that is too small — less than 3 feet on a side — may not generate enough heat; combine it with another pile or add more material.

If you see rodents or smell decay, you likely added meat, dairy, or oils. Remove those materials if you can identify them, bury food scraps deeper under browns, and consider using a rodent-proof bin instead of an open pile.

Frequently Asked Questions

Can I compost bread, pasta, and cooked food?

Cooked food, bread, and pasta can go in compost, but they attract rodents and flies more readily than raw vegetable scraps. Bury them deep under a thick layer of browns — at least 8 inches — and avoid adding them if you already have a pest problem. Raw vegetable scraps are safer.

What about citrus peels and onion skins?

Both are fine. Citrus peels take longer to break down than softer scraps, but they do decompose. Some gardeners worry that citrus slows decomposition, but in a balanced pile with plenty of greens and browns, they cause no problems. Onion skins break down quickly.

Can I add sawdust from my woodworking?

Only if the wood is untreated. Sawdust from pressure-treated lumber, plywood, or painted wood should not go in. Untreated hardwood sawdust is fine in small amounts mixed with other materials, though it breaks down slowly. Pine and softwood sawdust works but takes longer than leaves.

Is it okay to add weeds to compost?

Yes, as long as they have not set seed. If a weed has flowers or seed heads, leave it out — seeds survive composting and will spread when you use the finished product. Pulled weeds with no flowers are safe to add.

What if I accidentally added meat or dairy?

Remove it if you can see it. If you cannot locate it, add extra browns, turn the pile frequently to introduce oxygen, and monitor for rodents. In the future, keep a separate small container for meat and dairy scraps and put them in the trash instead.