The Basic Rule: Browns and Greens

You can compost anything that was once alive and will break down into soil. The easiest way to think about it: put in browns (dry, carbon-rich materials like leaves and cardboard) and greens (wet, nitrogen-rich materials like food scraps and grass clippings), keep them moist and turned, and they will become compost in weeks to months.

The reason this matters is that browns and greens break down at different rates and feed different microorganisms. A pile of only leaves will sit for a year. A pile of only food scraps will smell and attract pests. Mixed together in roughly equal amounts, they heat up, decompose fast, and smell like soil.

Key Takeaways

  • Fruit and vegetable scraps, coffee grounds, eggshells, and plant trimmings are safe to compost and break down quickly.
  • Meat, fish, dairy, oils, and pet waste should never go in a home compost bin because they attract pests or spread disease.
  • Leaves, grass clippings, shredded paper, and cardboard are excellent browns and greens that speed up decomposition.
  • Diseased plants, weeds with seeds, and treated wood will either spread problems or take years to break down.
  • Cooked food, grains, and nuts can compost but often attract rodents, so bury them deep in the pile or skip them.

Greens You Can Compost

Greens are wet, nitrogen-rich materials that heat up your pile and feed the bacteria doing the work. Fruit and vegetable scraps are the most common: apple cores, banana peels, carrot tops, lettuce, broccoli stems, onion skins, and potato peels all break down in weeks. Coffee grounds and tea bags (remove the staple) are greens too, and they decompose so fast that many people use them to jump-start a slow pile.

Fresh grass clippings, plant trimmings, and pulled weeds (without seed heads) are greens. So are crushed eggshells, which also add calcium as they break down. Seaweed and kelp from the beach work well if you rinse off the salt first. Avoid diseased plant material—if your tomato plant had blight, compost will not get hot enough to kill the spores, and you will spread the disease to next year's garden.

Browns You Can Compost

Browns are dry, carbon-rich materials that give the pile structure and air pockets. Dry leaves are the most obvious choice and the easiest to find in fall. Shredded newspaper, cardboard boxes (remove tape and staples), paper bags, and junk mail all compost well—the ink is soy-based or mineral-based now, not toxic. Straw and hay (not treated with herbicide) break down slowly but add bulk.

Wood chips and sawdust from untreated wood are browns, though they take longer than leaves—six months to a year. Never use treated wood, pressure-treated lumber, or plywood, because the chemicals will leach into your compost and then into your soil. Shredded cardboard from packaging is ideal because it breaks down faster than whole boxes and takes up less space. Avoid glossy or waxed cardboard, which has a plastic coating.

Foods That Attract Pests or Slow Decomposition

Cooked food, grains, bread, pasta, rice, nuts, and seeds can technically compost, but they attract rodents and insects. If you have a sealed, rodent-proof bin and you bury these materials deep in the center of the pile, they will break down. If you have an open pile or a bin with gaps, skip them. The smell and the pests are not worth it.

Meat, fish, bones, and shellfish should never go in a home compost bin. They decompose slowly, smell terrible, and attract rats and raccoons. Dairy products like milk, cheese, and yogurt do the same. Oils, fats, and grease coat the pile and prevent air from reaching the microorganisms, so decomposition stalls. If you want to compost these materials, you need a commercial facility with the heat and equipment to handle them safely.

What to Avoid Completely

Pet waste—dog or cat feces—should never go in a home compost bin. It carries pathogens that survive the composting process and can contaminate vegetables you eat. Diseased plants, as mentioned, will spread the disease to your garden. Weeds with mature seed heads will survive composting and sprout in your finished compost, undoing the work.

Treated wood, pressure-treated lumber, and plywood contain arsenic or copper compounds that will not break down and will poison your soil. Glossy or waxed paper, plastic-coated cardboard, and synthetic materials do not decompose. Charcoal and coal ash contain substances that slow decomposition; use only ash from untreated wood fires, and use it sparingly. Sawdust from treated wood or MDF (medium-density fiberboard) is off-limits for the same reason as treated lumber.

How to Speed Up Decomposition

The fastest compost happens when you balance browns and greens roughly equally by volume, keep the pile moist (like a wrung-out sponge), and turn it every week or two. Shredding or chopping materials before you add them speeds things up because smaller pieces have more surface area for microorganisms to work on. A 3-foot-by-3-foot pile with the right mix and regular turning can become finished compost in 6 to 8 weeks.

If you do not turn the pile, decomposition takes longer—3 to 6 months—but it still happens. The pile will heat up on its own as bacteria multiply, and you can tell it is working when steam rises from it on cool mornings. Adding a compost starter (a product with beneficial microorganisms) is optional; your pile will compost without it, though some people find it speeds things up slightly.

Frequently Asked Questions

Can I compost citrus peels and onions?

Yes, citrus peels and onion skins compost fine. They break down in weeks and do not harm the pile. The myth that they repel worms is false—worms will eat them. You can add them in any quantity without worry.

What about glossy magazine pages or colored paper?

Glossy magazines and colored paper have coatings that do not break down, so skip them. Plain newspaper, cardboard, and uncoated paper are safe. If you are unsure whether paper is coated, tear it—if it tears cleanly and the fibers are visible, it is fine.

Can I compost sawdust from my workshop?

Only if it is from untreated wood. Sawdust from pressure-treated lumber, plywood, or MDF contains chemicals that will not decompose and will contaminate your compost. If you are certain the wood was untreated, sawdust is a good brown, though it decomposes slowly.

Do I need to remove stickers from produce before composting?

Yes, remove stickers before composting. They are plastic and will not break down. The produce itself is fine—just peel off the label first.

Can I compost paper towels and napkins?

Yes, paper towels and napkins compost well as long as they are not contaminated with meat, grease, or chemicals. If they are covered in food scraps, that is fine—they will break down together. Avoid paper towels used to clean up oils or solvents.