What Goes on a Compost Heap

You can compost most plant material, food scraps, and yard waste. The basic rule is this: if it came from a plant or animal and will rot, it probably belongs in your heap. Grass clippings, leaves, vegetable peels, coffee grounds, crushed eggshells, shredded paper, cardboard, straw, and wood chips all break down into usable compost. The speed depends on what you add and how you manage moisture and air, but nearly all of these materials will eventually turn into dark, crumbly compost you can dig into garden beds.

The materials that work best fall into two categories: greens (nitrogen-rich, usually wet or fresh) and browns (carbon-rich, usually dry). Greens include vegetable scraps, grass clippings, plant trimmings, and manure from plant-eating animals. Browns include dried leaves, straw, shredded newspaper, cardboard, and wood chips. A working heap needs both—roughly three parts brown to one part green by volume—so the pile heats up, breaks down evenly, and does not smell like rotting garbage.

Key Takeaways

  • Vegetable scraps, fruit peels, grass clippings, leaves, and shredded paper all compost well and form the backbone of most home heaps.
  • Meat, fish, dairy, oils, and diseased plants should never go in a home compost heap because they attract pests, smell, or spread disease to your garden.
  • Cooked food, pet waste, and glossy or treated paper break down too slowly or introduce problems that make compost unsafe to use.
  • Mixing dry browns with wet greens in roughly a 3-to-1 ratio keeps your heap from becoming a smelly, waterlogged mess.

Vegetables, Fruit, and Kitchen Scraps That Compost Well

Almost any raw vegetable or fruit scrap works: carrot tops, potato peels, apple cores, banana skins, lettuce leaves, onion skins, and citrus peels. Chop larger pieces into smaller chunks so they break down faster. Coffee grounds and tea bags (remove the staple if there is one) add nitrogen and break down quickly. Crushed eggshells add calcium and take longer to decompose, but they do not hurt anything.

The one exception is avocado skin and pit—they contain compounds that can slow decomting and may harm plants, so leave them out. Likewise, onions and garlic in large quantities can repel worms, though a few skins mixed in cause no real problem. If you are unsure about a specific scrap, err on the side of leaving it out; you can always bury it deeper in the pile or skip it entirely.

Yard Waste and Plant Material

Grass clippings, leaves, plant trimmings, and flower stems are ideal compost material. Shred or chop leaves before adding them so they do not mat down and trap moisture. Grass clippings work best if you let them dry slightly first, because fresh, wet grass can clump and smell. Wood chips and sawdust from untreated wood break down slowly but add valuable carbon; avoid sawdust from pressure-treated or painted wood, which contains chemicals.

Straw and hay are excellent browns, though hay may contain weed seeds that survive the composting process. If you use hay, make sure your heap gets hot enough—a temperature of 140°F or higher for several days kills most seeds. Pine needles take years to decompose and can make your compost acidic, so use them sparingly or skip them. Diseased plant material should never go in a home heap; the temperature usually does not get high enough to kill pathogens, so you risk spreading disease to your garden next year.

Paper, Cardboard, and Other Materials to Avoid Misusing

Shredded newspaper, plain cardboard, and paper towels all compost, but with limits. Avoid glossy or coated paper (magazines, takeout boxes with plastic lining, paper with colored ink) because the coating does not break down and may contain chemicals. Cardboard is fine, but remove tape, staples, and plastic windows first. Shred it into strips so it does not form a solid layer that blocks air and water.

Wood ash from a fireplace or wood stove can go in compost, but only in small amounts—too much raises the pH and can harm plants. Charcoal ash should not go in at all; it contains chemicals. Sawdust from untreated wood is acceptable; sawdust from treated, painted, or stained wood is not. If you are not certain whether wood has been treated, leave it out.

What Never Goes in a Home Compost Heap

Meat, fish, bones, and any animal product except manure will attract rats, raccoons, and other pests. They also smell terrible as they rot. Dairy products (milk, cheese, butter, yogurt) do the same. Oils, fats, and grease break down very slowly and can waterlog your heap. Cooked food of any kind—even vegetable scraps that have been cooked—should stay out because the heat and moisture can create conditions that favor harmful bacteria and attract pests.

Pet waste (dog or cat feces) should never go in a home heap. It can contain parasites and pathogens that survive the composting process and contaminate your soil. Diseased plants, weeds with seeds, and invasive plants like bindweed or Japanese knotweed should not go in unless you are certain your heap reaches and maintains 140°F for at least three days—most home heaps do not. Glossy paper, plastic-lined cardboard, and treated wood all contain substances that do not break down or leach chemicals into your compost.

How Temperature and Moisture Affect What You Can Add

A hot compost heap—one that reaches 130°F to 150°F—breaks down material faster and kills weed seeds and some pathogens. To reach this temperature, you need the right mix of greens and browns, adequate moisture (like a wrung-out sponge), and regular turning. If your heap stays cool, you can still compost, but it takes longer and you should be more cautious about what you add. Diseased plants, weed seeds, and pet waste are riskier in a cool heap.

Moisture matters too. A heap that is too wet becomes anaerobic (oxygen-starved) and smells like rotten eggs. A heap that is too dry breaks down slowly. If you add a lot of wet greens (grass clippings, fresh plant trimmings), balance them with dry browns (leaves, cardboard, straw). If your heap is soggy, stop adding greens and add more dry material. If it is bone-dry, water it lightly or add more fresh material.

Frequently Asked Questions

Can I compost bread, pasta, and grains?

Raw grains and uncooked pasta can go in, though they break down slowly. Cooked bread, pasta, and rice should stay out because they attract pests and can create a gluey, anaerobic layer in your heap. If you want to compost these, bury them deep in the center of a hot, active heap where pests cannot easily reach them.

What about weeds and grass with seeds?

Grass clippings from a mowed lawn are fine—the mower cuts the seeds into pieces that do not sprout. Weeds with visible seed heads should not go in unless your heap reaches 140°F and stays there for several days. If you are unsure, leave them out or bury them in the hottest part of your heap.

Can I put sawdust from my workshop in the compost?

Only if it is from untreated, unfinished wood. Sawdust from pressure-treated lumber, plywood, MDF, or painted wood contains chemicals and should never go in compost. If you are not certain what the wood is, leave the sawdust out.

Is it okay to add a little bit of meat or fish?

No. Even small amounts of meat, fish, or bones attract rodents and create odor problems. They also take much longer to decompose than plant material. Stick to plant-based scraps only.

What should I do with compostable bags and packaging?

Most compostable bags are designed for industrial composting facilities that reach higher temperatures than home heaps. They may not break down in a home compost pile. Check the label; if it says "home compostable," it is safe to add. Otherwise, leave it out or check with your local industrial composting program.