The Basic Rule: Browns and Greens

You can compost most things that came from a plant or animal. The easiest way to think about it is browns (dry, carbon-rich materials) and greens (wet, nitrogen-rich materials). Browns include dry leaves, shredded paper, cardboard, and wood chips. Greens include grass clippings, vegetable scraps, coffee grounds, and plant trimmings. A working compost pile needs both — roughly three parts brown to one part green — so the pile breaks down evenly without turning into a wet, smelly mess.

The reason this matters is that browns let air flow through the pile, while greens provide the nitrogen that feeds the microbes doing the actual decomposition. If you add only grass clippings, you get a compacted, anaerobic sludge. If you add only leaves, decomposition slows to a crawl. The balance is what makes compost work.

Key Takeaways

  • Vegetable scraps, fruit peels, coffee grounds, and crushed eggshells are safe greens that break down quickly in any home compost system.
  • Meat, fish, dairy, oils, and pet waste should never go in a home compost pile because they attract pests and create odor problems.
  • Diseased plants, weeds with seeds, and treated wood should be kept out because they can survive the composting process and cause problems in your garden.
  • Shredded paper and cardboard are excellent browns, but glossy paper, colored inks, and treated cardboard can introduce chemicals into your finished compost.
  • Grass clippings and leaves are free greens and browns, but only use them if they have not been treated with pesticides or herbicides.

Vegetable and Fruit Scraps That Decompose Quickly

Vegetable peels, cores, and trimmings break down in weeks rather than months. Carrot tops, broccoli stems, lettuce leaves, onion skins, and potato peels all work. Fruit scraps — apple cores, banana peels, citrus rinds, melon rinds — decompose readily, though citrus takes longer than softer fruits. Crushed eggshells add calcium and break down over time, though whole shells take much longer.

The one exception is avocado pits and peels. The pit takes so long to decompose that most home composters skip it. Avocado peels are fine. Coffee grounds and tea bags (remove the staple first) are excellent additions and add nitrogen. Used paper coffee filters also compost.

Paper, Cardboard, and Wood Materials

Shredded newspaper, plain cardboard, and cardboard egg cartons are safe browns. Tear or shred them into pieces so they break down faster. Corrugated cardboard boxes work, but remove tape and labels first. Paper towel and toilet paper tubes are fine. Wood chips and sawdust from untreated wood are excellent browns, though they decompose slowly — use them if you have patience or a hot, active pile.

Do not compost glossy paper, colored inks, or coated cardboard. Pizza boxes have grease and should be skipped. Treated wood, plywood, and particle board contain glues and chemicals that do not break down and will contaminate your finished compost. Paper with plastic coating — like some coffee cups or takeout containers — should also stay out.

What Never Goes in Home Compost

Meat, fish, bones, and poultry attract rats, raccoons, and flies. Dairy products, oils, and fats do the same and create rancid smells. Pet waste (dog or cat feces) can harbor pathogens that survive home composting temperatures. Human waste should never be composted at home. Diseased plants and weeds with mature seeds can survive the process and spread problems to your garden later.

Treated wood, pressure-treated lumber, and plywood contain arsenic or other preservatives. Glossy or colored paper, synthetic materials, plastics, and rubber do not decompose. Charcoal ash (from grills) contains chemicals; wood ash from a fireplace is fine in small amounts. Sawdust from treated or painted wood should be avoided. Synthetic fertilizers and pesticides do not belong in compost either — they do not break down and can harm soil life.

Grass Clippings and Leaves: Free Materials with Caveats

Grass clippings are nitrogen-rich greens and cost nothing if you have a lawn. Shred them with a mower before adding so they do not mat down. Leaves are abundant browns in fall and are one of the best free compost materials available. Shred them with a mower or leaf blower to speed decomposition. Both work best if they come from a lawn or yard that has not been treated with pesticides or herbicides — chemical residues will end up in your finished compost and then in your garden soil.

If you use a lawn service or explore weed killer yourself, wait at least two to three weeks before collecting clippings for compost. Better yet, ask the service whether they use organic methods. Leaves from diseased trees (like those with anthracnose or other fungal issues) should be burned or bagged for disposal rather than composted, since home piles may not get hot enough to kill the pathogens.

Plant Trimmings and Garden Waste

Healthy plant trimmings, prunings, and spent garden plants all compost. Tomato vines, bean plants, squash stems, and flower deadheadings are fine. Straw and hay (as long as they are not moldy) work as browns. Pine needles and conifer trimmings compost very slowly because they are acidic and tough, but they will eventually break down.

Do not compost plants infected with blight, mildew, or other diseases — the pathogens often survive home composting. Weeds with seed heads should be excluded because seeds can germinate in your finished compost or in your garden later. Invasive plants like bindweed or bermuda grass should be burned or disposed of separately, not composted, because fragments can regrow.

Special Materials: Sawdust, Straw, and Others

Sawdust from untreated wood is a good brown, though it compacts easily and should be mixed with coarser materials. Straw (not hay, which has seeds) is an excellent brown. Wool, cotton, and natural fiber scraps break down, though they take time. Newspaper and cardboard shredded together create a good brown base. Wood ash from a fireplace can be added in small amounts — it raises pH and adds potassium, but too much makes the pile too alkaline.

Do not use sawdust from treated, painted, or stained wood. Charcoal ash from a grill contains lighter fluid or other chemicals. Glossy or colored paper, synthetic fabrics, and anything with plastic coating should be kept out. Dryer lint is sometimes composted, but only if your clothes are natural fibers and you have not used fabric softener or dryer sheets, which contain synthetic compounds.

Frequently Asked Questions

Can I compost citrus peels and onion skins?

Yes, both compost fine. Citrus peels take longer than softer fruits — sometimes several months — but they will break down. Onion skins are quick to decompose. Some gardeners worry that citrus repels worms, but in a standard compost pile this is not a problem. If you are vermicomposting (using a worm bin), add citrus sparingly because worms do avoid it.

What about cooked food scraps?

Cooked vegetables with no oil or seasoning can go in, though they break down slowly and may attract pests. Cooked rice, pasta, and bread are fine in small amounts. Avoid anything cooked with oil, butter, meat, or dairy — these attract rodents and create odor. If you are unsure, leave it out.

Can I compost paper with colored ink?

Newspaper with black ink is safe. Glossy magazines, colored inks, and coated papers should be avoided because the inks and coatings may contain heavy metals or other chemicals that do not break down and end up in your soil. Stick with plain paper and cardboard.

How do I know if my wood chips are treated?

Treated wood is usually labeled or stamped. Pressure-treated lumber is often greenish or has a chemical smell. If you are not sure, do not use it. Untreated wood chips from a tree service are usually safe, but ask whether the wood came from treated lumber or was treated with any preservative before you accept it.

Can I compost diseased plant material?

Home compost piles typically do not reach the sustained high temperatures needed to kill most plant pathogens. Diseased plants should be bagged for disposal or burned if local regulations allow. This prevents spreading the disease to your garden through finished compost.