The Basic Rule: Browns and Greens, Nothing Toxic or Oily

Compost piles break down two types of material: browns (carbon-rich: dry leaves, straw, shredded paper, cardboard) and greens (nitrogen-rich: grass clippings, food scraps, plant trimmings). The pile needs both to heat up and decompose properly. What you cannot add is anything that will slow decomposition, attract pests, create odor, or introduce chemicals into the finished compost—mainly meat, dairy, oils, diseased plants, and treated wood.

The reason matters: a compost pile is a living system. Bacteria and fungi do the work, and they thrive on plant material and certain food scraps. Meat and dairy feed the wrong organisms—the ones that create smell and draw rats. Oils coat particles and block air flow. Diseased plants spread infection to your garden. Treated wood leaches toxins. Understanding what belongs and what doesn't keeps your pile working fast and your finished compost safe to use.

Key Takeaways

  • Add all raw fruit and vegetable scraps, coffee grounds, tea bags, crushed eggshells, and grass clippings without hesitation.
  • Never add meat, fish, bones, dairy, oils, fats, or cooked food—these attract pests and create odor.
  • Diseased plants, weeds with seeds, and pet waste do not belong in home compost because they can survive the pile and spread problems to your garden.
  • Shredded paper, cardboard, leaves, and straw are safe browns; glossy paper, treated wood, and charcoal ash are not.
  • A working pile needs roughly three parts brown material to one part green material by volume.

What Goes In: Greens (Nitrogen-Rich Materials)

Greens are the "wet" materials that heat up the pile and feed the microbes. Fresh grass clippings, vegetable and fruit scraps (raw only), coffee grounds and filters, tea bags, crushed eggshells, and plant trimmings all break down quickly. Seaweed and kelp are excellent if you have access to them. Manure from herbivores—horse, cow, chicken, rabbit—also works, though aged manure is safer than fresh because it has already begun to cool.

The safest rule for food scraps: if you would eat it raw, it can go in. Raw apple cores, carrot peels, lettuce, broccoli stems, banana peels, melon rinds—all fine. Citrus peels take longer to break down but do decompose. Onion and garlic scraps are safe despite their smell; the pile will smell like compost, not like rotting food. Avoid anything cooked, salted, oiled, or sweetened.

What Goes In: Browns (Carbon-Rich Materials)

Browns are the "dry" materials that add structure, allow air to flow, and balance the moisture from greens. Dry leaves, straw, hay, shredded newspaper, cardboard (remove tape and labels), wood chips, sawdust from untreated wood, and pine needles all work. Shredded paper from a home shredder is fine; so are paper towel and toilet paper tubes. Straw is better than hay because hay often contains weed seeds, though either will eventually decompose.

The pile needs roughly three times as much brown material by volume as green material. If your pile smells like ammonia or rotten eggs, you have too much green and not enough brown—add more dry leaves or shredded paper. If it is not heating up or breaking down, you may have too much brown; add more grass clippings or food scraps. A balanced pile will feel warm in the center within a few days of turning.

What Never Goes In: Meat, Dairy, and Oils

Meat, fish, bones, and any animal product except manure from plant-eating animals will attract rats, raccoons, and flies. Dairy—milk, cheese, yogurt, butter—does the same and creates a sour smell that lingers. Oils, fats, grease, and salad dressing coat the pile and prevent air from reaching the microbes, which slows decomposition and creates anaerobic (airless) pockets that smell like rotten eggs.

This is the most common mistake home composters make: adding a chicken bone or leftover pasta with oil, then wondering why the pile smells terrible and rodents show up. If you have a small amount of cooked food waste, a municipal compost program (if your city runs one) can handle it in an industrial-scale pile that reaches higher temperatures. Your home pile cannot.

What Never Goes In: Diseased Plants, Weeds, and Pet Waste

Diseased plant material—leaves with fungal spots, stems with blight, roots with root rot—can survive a home compost pile and infect your garden when you use the finished compost. The same applies to weeds that have gone to seed; the seeds often survive and you end up spreading the weeds you were trying to avoid. If you are unsure whether a plant is diseased, leave it out. Healthy plant trimmings are free; a garden full of disease is not worth the risk.

Pet waste—dog or cat feces—should never go in a home compost pile. It can harbor parasites and pathogens that survive the pile and contaminate vegetables you grow. Some municipal programs accept pet waste in industrial composting, but home piles do not reach the sustained high temperature needed to kill these organisms safely.

What Never Goes In: Treated Materials and Ash

Treated wood, plywood, particle board, and wood that has been painted or stained contain glues and chemicals that do not break down and will contaminate your compost. Sawdust from treated wood is equally unsafe. Charcoal ash from a grill or fireplace contains residues and should not go in; wood ash from a wood stove is fine in small amounts (it raises pH), but charcoal ash does not. Glossy or colored paper, magazines, and junk mail may contain inks and coatings that are not food-safe.

Pressure-treated lumber is especially dangerous because it contains arsenic or copper compounds designed to resist rot. Even though the wood is old and weathered, those compounds remain in the sawdust and wood chips. If you are unsure whether wood has been treated, assume it has and leave it out.

How to Build a Balanced Pile

Start with a layer of coarse brown material—straw or wood chips—about 6 inches deep. This allows air to flow from the bottom. Add a layer of green material (grass clippings, food scraps, plant trimmings) about 2 inches deep. Alternate layers, keeping the ratio roughly 3 parts brown to 1 part green by volume. Water each layer lightly as you build; the pile should feel like a wrung-out sponge, not soggy and not bone-dry.

Turn the pile every week or two by moving material from the outside edges to the center, where it is hottest. A well-maintained pile will heat to 130 to 150 degrees Fahrenheit in the center and break down to finished compost in 4 to 8 weeks. If you do not turn it, decomposition takes 6 months to a year. Either way works; turning just speeds it up.

Frequently Asked Questions

Can I put bread, pasta, and rice in the compost?

Raw bread dough and uncooked rice or pasta can go in, though they break down slowly. Cooked pasta, rice, and baked bread should not go in because they attract pests and can mold before the pile heats up. If you have a lot of cooked grain waste, a municipal program is a better choice.

What about paper towels and napkins?

Plain white paper towels and napkins break down fine and are a good brown material. Avoid paper towels or napkins that have been used with oils, grease, or meat. Paper towels used to wipe up spills are usually safe; those used to clean up cooking oil are not.

Can I compost pine needles and evergreen branches?

Yes. Pine needles and evergreen trimmings decompose slowly because they are acidic and tough, but they will eventually break down. Shred them if possible to speed the process. They are an excellent brown material if you have access to them.

Is it okay to add weeds that have not gone to seed?

Yes, as long as they have no seed heads and no roots that will regrow. Young weeds pulled before flowering are safe. Mature weeds, dandelions with seed heads, and anything with a thick root system should be left out because roots can survive and regrow in your garden.

What should I do if my compost pile smells bad?

A rotten-egg or ammonia smell means the pile is too wet or has too much green material and not enough air. Add dry leaves or shredded paper, turn the pile to add oxygen, and reduce how much food scrap you add each week. A properly balanced pile should smell earthy, not foul.