The Basic Rule: Browns and Greens in Balance

A working compost bin needs two types of material: greens (nitrogen-rich, wet materials) and browns (carbon-rich, dry materials). The right ratio is roughly three parts brown to one part green by volume. Greens heat up the pile and speed decomposition; browns provide structure so air can flow through. Without both, you get either a soggy, smelly mess or a pile that barely breaks down.

The easiest way to think about it: if you can eat it or it grew from a plant, it probably goes in. If it's woody, paper, or already dead plant matter, it's a brown. Meat, dairy, oils, and pet waste do not go in any residential compost bin—they attract pests, create odor, and can harbor pathogens that home composting temperatures don't kill.

Key Takeaways

  • Greens include fruit and vegetable scraps, coffee grounds, fresh grass clippings, and plant trimmings; browns include dry leaves, shredded paper, cardboard, and wood chips.
  • Never add meat, fish, dairy, oils, fats, pet waste, diseased plants, or weeds with seeds—these create odor, pests, or contamination.
  • Layer materials as you add them: a few inches of brown, then a few inches of green, then brown again, to keep the pile balanced and aerated.
  • Chop or shred larger items before adding them so they break down faster and pack less densely in the bin.
  • If your pile smells bad or attracts insects, you likely have too much green material or too much moisture; add more brown and mix the pile.

Greens: Nitrogen-Rich Materials That Heat the Pile

Greens are the fresh, moist materials that microbes consume quickly. Fruit and vegetable scraps are the most common: apple cores, banana peels, carrot tops, lettuce leaves, squash seeds, onion skins, and stale bread all break down readily. Coffee grounds and tea bags (remove the staple from tea bags) are excellent greens and add nitrogen. Fresh grass clippings work, but use them sparingly—they mat down and can create a slimy layer if you add too much at once.

Plant trimmings from your garden count as green if they're fresh and soft: deadheaded flowers, tender herb stems, and young weeds without seeds. Seaweed and kelp are strong greens if you live near the coast. Avoid diseased plant material; if a plant had powdery mildew, blight, or rust, leave it out so you don't spread the disease to your garden later.

Browns: Carbon-Rich Materials That Build Structure

Dry leaves are the workhorse brown. Shred them first if you can—a mower run over a pile of leaves works perfectly—because whole leaves pack down and exclude air. Shredded paper, cardboard (remove tape and labels), and newspaper are all acceptable browns; avoid glossy magazines and colored inks. Wood chips, sawdust from untreated wood, and straw (not hay, which contains seeds) provide good carbon and airflow.

Pine needles and wood ash can go in, but use them cautiously. Pine needles are acidic and break down slowly, so mix them with other materials rather than layering them thick. Wood ash from a fireplace or wood stove is fine in small amounts, but it raises pH; don't add more than a handful per month to an average bin. Never use charcoal briquette ash—it contains chemicals.

What Never Goes in a Home Compost Bin

Meat, fish, and bones attract rats, raccoons, and flies. Dairy products like milk, cheese, and yogurt also draw pests and create foul odors. Oils, fats, and grease—including salad dressing, butter, and meat drippings—slow decomposition and can waterlog the pile. Pet waste from dogs and cats harbors pathogens that home compost temperatures (usually 130–150°F) don't reliably kill; only industrial composting reaches the 160°F needed to neutralize them.

Avoid diseased plants, weeds with mature seeds, and invasive plants like bindweed or morning glory. The compost pile may not get hot enough to kill seeds or pathogens. Glossy paper, treated wood, and sawdust from pressure-treated lumber contain chemicals that persist in finished compost. Coal or charcoal ash is different from wood ash and should not be added. Citrus peels and onion skins are fine in moderation, but large amounts can slow decomposition and repel worms.

How to Layer and Add Materials Over Time

The simplest method is to layer as you go: add a 3- to 4-inch layer of brown material, then a 1- to 2-inch layer of green, then brown again. This keeps the pile balanced and ensures air pockets stay open. If you're adding a large batch of grass clippings or leaves, break it up and mix it with brown material rather than dumping it all at once.

Chop or shred larger items before adding them. A whole apple takes months to break down; chopped apple pieces decompose in weeks. Tear cardboard into fist-sized pieces rather than adding whole sheets. The smaller the pieces, the faster microbes can work and the less space the pile takes up. If you have a food processor or blender you're replacing, use it to shred vegetable scraps before composting.

Troubleshooting: When Your Pile Isn't Working Right

If your compost smells like ammonia or rotten eggs, you have too much green material or too much moisture. Stop adding greens, mix the pile to add air, and layer in dry brown material. If the pile is cold and barely breaking down after several weeks, it's too dry or has too much brown. Add water and more green material, then mix. If flies or fruit gnats appear, you likely have exposed food scraps; bury new greens under a layer of brown material.

Rodents are a sign that meat, dairy, or oil got into the bin. Remove the offending material if you can find it, and cover all food scraps with at least 4 inches of brown material going forward. If the pile is soggy and compacted, turn it and add shredded brown material to improve drainage and aeration. Most problems come from too much green or too much moisture—brown material and air are the fix.

Frequently Asked Questions

Can I compost cooked food?

Cooked vegetables and grains are fine; cooked meat, fish, dairy, and oily foods are not. Cooked food also attracts pests more readily than raw scraps, so bury it deep under brown material. Plain cooked rice, pasta, and vegetable scraps break down like raw ones.

Do I need to shred everything before adding it?

No, but shredding speeds decomposition significantly. Whole apple cores take months; chopped pieces take weeks. Shredding is most important for large items, cardboard, and leaves. Small scraps like coffee grounds and vegetable peelings don't need shredding.

Can I add sawdust from my workshop?

Only if it's from untreated wood. Sawdust from pressure-treated lumber, plywood, or particle board contains chemicals that persist in compost. If you're unsure whether the wood was treated, leave it out. Untreated sawdust is an excellent brown material.

How often should I add material to my bin?

Add material whenever you have it—there's no strict schedule. Some people add scraps daily; others collect them in a small container and add a batch once a week. The more often you add and mix, the faster the pile breaks down, but even an unmixed pile will eventually compost.

Can I compost weeds from my garden?

Young weeds without seeds are fine. If the weeds have gone to seed or have deep roots like dandelions, leave them out. Compost piles don't always get hot enough to kill seeds, and you'll end up spreading weeds when you use the finished compost in your garden.