What Goes Into a Compost Bin

A compost bin breaks down two types of material: greens (nitrogen-rich items) and browns (carbon-rich items). Greens are usually wet and fresh—fruit scraps, vegetable peels, grass clippings, coffee grounds. Browns are usually dry—leaves, shredded paper, cardboard, wood chips. You need both to make compost work. A bin that has only greens will smell bad and turn into mush. A bin with only browns will sit there for years and barely change.

The basic rule: if it came from a plant or animal and will rot, it probably belongs in your bin. But "probably" is not the same as "definitely." Some things rot too slowly, attract pests, or introduce chemicals you do not want in your finished compost. The sections below tell you what works, what does not, and why.

Key Takeaways

  • Fruit and vegetable scraps, coffee grounds, and crushed eggshells are safe greens that speed up decomposition.
  • Leaves, shredded paper, cardboard, and wood chips are browns that provide structure and prevent odors.
  • Meat, fish, dairy, oils, and diseased plants should never go in a home compost bin because they attract pests or spread infection.
  • Grass clippings and plant trimmings work well, but only if they have not been treated with pesticides or herbicides.
  • Aim for a ratio of roughly three parts brown to one part green by volume to keep your bin balanced.

Greens That Belong in Your Bin

Greens are the fast-working part of compost. They heat up the pile and feed the microbes that do the actual breaking down. Fruit scraps—apple cores, banana peels, melon rinds—go in whole or chopped. Vegetable scraps work the same way: carrot tops, broccoli stems, onion skins, lettuce leaves. The smaller you chop them, the faster they break down, but whole pieces will eventually decompose too.

Coffee grounds and tea bags (remove the staple from tea bags first) are excellent greens. So are crushed eggshells, though they take longer to break down than other scraps. Fresh grass clippings work, but only if your lawn has not been treated with herbicides or pesticides in the last month or two—chemicals linger in the clippings and can end up in your finished compost. Plant trimmings from indoors or outdoors are fine as long as the plant was healthy and not treated with fungicide or insecticide.

Browns That Keep Your Bin Balanced

Browns are the structure and the brake on your compost pile. They absorb moisture, prevent the pile from compacting into a wet brick, and slow decomposition to a manageable pace. Dry leaves are the easiest brown to find in fall. Shred them with a mower or by hand before adding them—whole leaves mat down and trap air. Shredded paper and cardboard work well too. Newspaper, junk mail, and plain cardboard boxes are all fine. Avoid glossy paper, colored inks, and cardboard with plastic tape.

Wood chips, sawdust, and straw are good browns if you have access to them. Sawdust from untreated wood is safe; sawdust from pressure-treated lumber is not. Straw (not hay, which contains seeds) adds bulk without introducing weed seeds into your finished compost. Shredded leaves mixed with cardboard strips is the easiest combination for most home composters to maintain.

What Never Goes in a Home Compost Bin

Meat, fish, bones, and any other animal flesh will rot in a compost bin, but they attract rats, raccoons, and flies while they do. Home bins do not get hot enough or stay sealed well enough to kill pathogens that live on raw meat. Dairy products—milk, cheese, yogurt, butter—have the same problem: they smell terrible as they break down and draw pests. Oils and fats, including cooking oil and grease, coat other materials and slow decomposition. They also smell.

Diseased plants should never go in a home bin. Fungal infections like powdery mildew and bacterial wilts can survive the composting process and spread to your garden when you use the finished compost. If a plant was visibly sick, throw it in the trash instead. The same goes for weeds that have gone to seed—your bin probably will not get hot enough to kill all the seeds, and you will end up spreading weeds when you spread the compost.

Avoid pet waste (dog or cat feces), used kitty litter, and diseased animal bedding. These carry pathogens that survive home composting. Glossy or colored paper, cardboard with plastic coating, and treated wood also belong in the trash. Synthetic materials like plastic, rubber, and metal do not belong in any compost bin.

Treated and Chemically Sprayed Materials

Grass clippings and plant trimmings from lawns or gardens treated with herbicides, pesticides, or fungicides should not go in your bin. These chemicals do not break down during composting—they end up in your finished compost and then in your garden soil. If you are not sure whether your lawn or a neighbor's has been treated, wait at least two weeks after any visible spraying before adding clippings to your bin.

Pressure-treated wood, wood stained with chemical finishes, and plywood with glue binders should all stay out. Sawdust from these materials is especially risky because it is straightforward to accidentally mix it with your compost. If you have access to untreated wood scraps or sawdust from a woodworker who uses only raw wood, those are safe to add in small amounts.

How to Balance Your Bin for Best Results

The ideal ratio is roughly three parts brown to one part green by volume. This means if you add a bucket of vegetable scraps, add three buckets of shredded leaves or cardboard. In practice, most home composters do not measure this precisely—they layer browns and greens as materials become available and adjust if the pile starts to smell (too many greens) or stops breaking down (too many browns).

A bin that smells like ammonia or rotten eggs has too many greens. Add more browns and turn the pile if your bin has a door or is small enough to move. A bin that is not heating up or breaking down after several months probably has too many browns or not enough moisture. Add some greens and water it lightly. Most home bins reach a usable state in three to six months if you maintain the balance and turn the pile occasionally.

Frequently Asked Questions

Can I put cooked food in my compost bin?

No. Cooked food attracts pests the same way raw meat does, and the oils and fats in cooked dishes slow decomposition. Stick to raw fruit and vegetable scraps only.

What about citrus peels and onions?

Citrus peels and onion skins are safe to compost, but add them in moderation. Large amounts of citrus can slow decomposition because the acidity takes time to break down. Onions are fine in normal quantities.

Can I put pine needles or conifer leaves in my bin?

Yes, but use them sparingly. Pine needles and conifer leaves break down very slowly and are quite acidic. Mix them with other browns rather than adding large amounts at once.

Is it okay to add glossy magazine pages or newspaper with color ink?

Plain newspaper is safe. Glossy magazines and pages with heavy color inks should go in the recycling bin instead. The inks and coatings do not break down in home composting.

What if I accidentally put meat or dairy in my bin?

Remove it if you can see it. If it is already mixed in, cover it with a thick layer of browns and monitor your bin for pest activity. If you notice rats or flies, you may need to empty and restart the bin in a different location.