Browns and Greens: The Two Categories That Matter
A working composter needs two types of material: browns (carbon-rich) and greens (nitrogen-rich). Browns are dry, dead plant matter—leaves, straw, shredded paper, cardboard. Greens are fresh plant scraps and grass clippings. The pile breaks down fastest when you layer them roughly equally by volume, though exact ratios are forgiving. If your pile smells like ammonia or looks slimy, you have too many greens; add more browns and turn it. If nothing is breaking down after months, you likely have too many browns; add kitchen scraps or grass.
The reason this split matters is that microbes and fungi need both carbon (to build their bodies) and nitrogen (to reproduce). A pile of only leaves will sit for years. A pile of only food scraps will rot into a stinking mess. Together, they heat up, dry out properly, and turn into dark, crumbly compost in weeks to months depending on your climate and how often you turn the pile.
Key Takeaways
- Kitchen scraps like vegetable peels, fruit, coffee grounds, and eggshells are greens and break down quickly in a composter.
- Meat, fish, dairy, oils, and pet waste should never go in a home composter because they attract pests or spread disease.
- Leaves, straw, shredded paper, and cardboard are browns that balance greens and speed decomposition.
- Diseased plants, weeds with seeds, and treated wood should be kept out to avoid spreading problems to your garden.
- Grass clippings work as greens if they have not been treated with herbicide, and they heat up a pile faster than most other materials.
Kitchen Scraps That Belong in Your Composter
Vegetable and fruit scraps are the easiest materials to compost. Carrot peels, apple cores, lettuce leaves, onion skins, banana peels, melon rinds, and citrus peels all break down readily. Coffee grounds and tea bags (remove the staple from tea bags first) are nitrogen-rich and heat up a pile. Eggshells take longer to decompose but add calcium and do not cause problems—crush them first to speed the process.
Cooked vegetables without oil or sauce can go in, though raw scraps break down faster. Nuts and seeds will compost but take months; whole nuts are harder for microbes to penetrate. Bread, pasta, rice, and grains compost but may attract rodents if your bin is not fully enclosed, so bury them under a layer of browns. The rule is straightforward: if it came from a plant and has no oil, meat, or dairy on it, it will compost.
What Never Goes in a Home Composter
Meat, fish, bones, and any animal products except eggshells and manure attract rats, raccoons, and flies. Dairy products like milk, cheese, and yogurt smell terrible as they break down and also draw pests. Oils, butter, and grease coat other materials and slow decomposition. These items belong in the trash or, in some areas, in a separate food waste collection program run by your city.
Pet waste from dogs and cats should not go in a home composter because it can carry parasites and pathogens that survive the composting process and contaminate your garden soil. Diseased plants and weeds with mature seeds will spread those problems to whatever you grow later. Treated wood, glossy paper, and anything with ink or dyes may contain chemicals that persist through composting. Plastic, glass, and metal obviously do not break down.
Yard Waste: Leaves, Grass, and Branches
Fall leaves are the classic brown material—pile them up and they will eventually become dark, crumbly leaf mold. Shred them with a mower first if you have the time; smaller pieces decompose faster. Pine needles and evergreen clippings are very slow to break down and acidic, so use them sparingly unless you are composting for acid-loving plants like blueberries.
Fresh grass clippings are excellent greens and heat up a pile quickly, but only if they have not been sprayed with herbicide or fungicide. Clippings from a lawn treated with weed killer will kill the microbes in your composter and contaminate the finished product. If you are unsure about your lawn's history, leave grass clippings out. Small twigs and branches can go in, but thick woody stems take years to decompose; chip them first or leave them out. Sawdust from untreated wood is a fine brown, but sawdust from pressure-treated lumber is toxic.
Paper, Cardboard, and Other Household Materials
Shredded newspaper, cardboard boxes (remove tape and staples), and plain paper are excellent browns. Wet them down as you layer them so they do not blow away and so they break down faster. Cardboard egg cartons, paper towel tubes, and paper bags all work. Glossy paper, colored inks, and anything coated with plastic or wax should stay out—the coating does not break down and may contain chemicals.
Junk mail with colored ink is fine in small amounts; the inks used today are generally soy-based and not toxic. Magazines and catalogs are slower to decompose than newspaper because of their density, so shred them. Paper with a plastic window (like some envelopes) should be removed before composting. The rule is: plain paper and cardboard yes, anything coated or laminated no.
Special Materials: Manure, Straw, and Wood Chips
Animal manure from herbivores—horse, cow, chicken, rabbit—is nitrogen-rich and heats up a pile dramatically. Fresh manure can burn plants if applied directly, but composted manure is safe and excellent for soil. Let fresh manure age in the compost pile for at least three months before using the finished product on vegetables. Manure from animals treated with antibiotics or deworming medications will carry those chemicals into your compost, so source it from farms that do not use them if you plan to grow food.
Straw (the hollow stalks left after grain is harvested) is a brown and breaks down slowly but adds structure to the pile. Hay (dried grass with seeds still in it) should be avoided because those seeds will sprout in your garden. Wood chips from untreated trees are a brown but take years to fully decompose; use them as a top layer if you want, but do not expect them to turn into finished compost quickly. Sawdust from a sawmill is fine; sawdust from a hardware store cutting service may be from treated wood.
How to Layer and Balance Your Pile
The simplest approach is to alternate layers: a few inches of browns, then a few inches of greens, then browns again. Water each layer lightly as you build so the pile stays moist but not soggy. Aim for roughly equal volumes of each, though the exact ratio is not critical—your pile will tell you if it is wrong. If it smells sour or looks wet and matted, add more browns and turn it. If it is not heating up or breaking down after a month, add more greens.
Turning the pile (mixing it with a fork or shovel) speeds decomposition by introducing oxygen, which the microbes need. A pile turned weekly can produce finished compost in 4 to 8 weeks. A pile left alone will take 6 to 12 months. Either way works; turning is optional but faster. The finished product should be dark, smell earthy, and crumble in your hand with no recognizable scraps remaining.
Frequently Asked Questions
Can I compost citrus peels and onions?
Yes, both compost fine. Citrus peels take a few months to break down completely, and onions decompose quickly. Some gardeners worry that citrus slows worms in a worm bin, but in a regular hot compost pile, citrus is not a problem. Bury them under a layer of browns if you want to speed the process.
What about weeds—can I put them in if I pull them before they go to seed?
Young weeds without seed heads are fine. The problem is that some weed seeds survive the composting process, especially in a cold pile. If you are certain the weeds have no seeds and your pile heats above 140°F (which kills most seeds), you are safe. When in doubt, throw them in the trash.
Is it okay to compost glossy magazine pages?
Modern magazine inks are usually soy-based and not toxic, so small amounts are fine. The glossy coating slows decomposition, so shred the pages first. If you have a large pile of magazines, it is easier to recycle them. A handful mixed into a pile of kitchen scraps will not cause problems.
Can I put sawdust from my woodworking in the composter?
Only if the wood is untreated. Sawdust from pressure-treated lumber, plywood, or particle board contains chemicals that do not break down and will contaminate your compost. Sawdust from a sawmill or from untreated solid wood is a fine brown material.
What if I accidentally put meat in my composter?
Remove it if you can find it. If you cannot, bury it deep under a thick layer of browns and do not turn the pile for a few weeks—this discourages pests from digging. The meat will eventually decompose, but your pile may attract rodents in the meantime. Going forward, keep a separate container for meat scraps and put them in the trash.