Browns and Greens: The Two Categories That Matter
A compost bin works by breaking down two types of material: greens (nitrogen-rich, wet items) and browns (carbon-rich, dry items). You need both to get finished compost. Greens heat up the pile and speed decomposition. Browns slow it down, add structure, and prevent the pile from becoming a wet, smelly mess. The balance matters more than any single item you add.
Most successful home composters aim for a ratio of roughly three parts brown to one part green by volume, though the exact mix depends on what you have available and how fast you want the process to move. If your pile smells like ammonia or rotten eggs, you have too much green. If it is not heating up or breaking down, you need more green.
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.
- Meat, dairy, oils, diseased plants, and pet waste should never go in a home compost bin because they attract pests, create odor, or introduce pathogens.
- Grass clippings from lawns treated with herbicide or pesticide will kill beneficial microbes in your pile and should be kept out.
- Glossy or colored paper, coal ash, and pressure-treated wood break down slowly or introduce toxins and do not belong in compost.
- Shredding or chopping materials before adding them speeds decomposition by weeks or months compared to whole pieces.
Greens: What to Add From Your Kitchen and Yard
Fruit and vegetable scraps are the backbone of most home compost bins. Peels, cores, seeds, stems, and spoiled produce all break down readily. Coffee grounds and tea bags (remove the staple from tea bags first) add nitrogen and moisture. Crushed eggshells contribute calcium and take longer to break down, but they do not harm the pile. Plant-based food scraps like cooked rice, pasta, and bread can go in, though they may attract pests if not buried under browns.
Fresh grass clippings and plant trimmings from pruning are greens, but only if they have not been treated with herbicide or pesticide. Clippings from a lawn sprayed with weed killer will poison your compost and kill the microbes doing the work. If you are unsure whether your lawn has been treated, leave the clippings out. Seaweed and plant material from a pond or water feature also work well if rinsed of excess salt.
Browns: Dry Materials That Build Structure
Dry leaves are the most common brown and often free if you rake your own yard. Shred them first if possible—whole leaves mat down and decompose slowly. Shredded paper, cardboard (remove tape and labels), and newspaper all work. Avoid glossy or colored paper, which contains inks and coatings that do not break down. Plain kraft paper, newsprint, and plain cardboard are safe.
Wood chips, sawdust, and untreated wood shavings add carbon and air space. Straw and hay are browns, though hay may contain weed seeds that survive composting. Pine needles decompose very slowly and can make the pile acidic, so use them sparingly. Shredded leaves and cardboard are usually easier to source and faster to break down than wood products.
What Never Goes in a Home Compost Bin
Meat, fish, bones, and any animal product except eggshells attract rats, raccoons, and flies. Dairy products, oils, and fats do the same and create odor as they decompose. These items belong in the trash or a commercial composting facility, not a backyard bin.
Pet waste (dog or cat feces) and used cat litter carry pathogens that home compost does not get hot enough to kill. Human waste should never be composted at home. Diseased plants, plants infested with pests, and weeds with mature seeds can spread the problem to your garden when you use the finished compost. If you are unsure whether a plant is diseased, leave it out.
Coal ash and charcoal ash contain substances that harm plants and soil microbes. Wood ash from a fireplace or wood stove can go in small amounts (it raises pH), but coal ash cannot. Pressure-treated wood, plywood, and composite wood products contain glues and preservatives that do not break down and introduce toxins into your compost.
Items That Slow Down or Complicate Composting
Citrus peels, onion skins, and garlic break down eventually but can slow the process and repel some beneficial organisms. They are not forbidden, but add them sparingly and bury them under browns. Avocado pits and peach pits take months to decompose and are better left out unless you are patient.
Glossy or waxed paper (like takeout containers or bakery boxes) does not break down in a home bin. Synthetic materials like plastic, rubber, and metal have no place in compost. Dryer lint contains synthetic fibers and is better off in the trash. Sawdust from treated wood or plywood should not be added, but sawdust from untreated wood is fine.
How to Prepare Materials Before Adding Them
Chopping or shredding materials before adding them is the single fastest way to speed decomposition. A food scrap that is cut into quarters breaks down weeks faster than a whole apple. Shredded leaves decompose in months instead of a year. If you have a shredder, leaf vacuum, or even a lawn mower, use it.
Bury food scraps under a layer of browns to keep odor down and pests away. Add materials in layers rather than dumping everything at once. Wet the pile as you build it if it is very dry. Turn or mix the pile every week or two if you want finished compost in two to three months; leave it alone for six months to a year and it will finish on its own.
Frequently Asked Questions
Can I compost onions and garlic?
Yes, but add them in small amounts and bury them under browns. They slow decomposition and can repel some beneficial organisms, so they are not ideal, but they will eventually break down and will not harm the pile.
What about paper towels and napkins?
Plain white paper towels and napkins are safe to compost. Avoid colored or printed napkins with inks. Shred them first to speed breakdown. Paper towels used to clean up meat or dairy should go in the trash instead.
Can I add sawdust from my workshop?
Only if it is from untreated wood. Sawdust from pressure-treated lumber, plywood, or composite materials contains glues and preservatives that introduce toxins. If you are unsure whether the wood was treated, leave the sawdust out.
Do I need to remove seeds from fruit before composting?
No. Seeds break down in the compost pile and will not sprout in your garden. The same is true for small pits. Large pits like avocado or peach pits take months to decompose and are better left out if you want faster results.
What if I accidentally added something I should not have?
If it is a small amount of meat or dairy, bury it deep under browns and monitor for odor and pests. If the pile smells or attracts animals, remove what you can and cover it with a thick layer of browns. For large amounts or items like plastic, remove them when ready.