Compost 101
Everything rots. You're just helping.
You can't really get compost wrong. You can only get it slow, or smelly. Here's what goes in, how to keep it happy, and what to do when it isn't.
Can I compost this?
Answers for a backyard pile, a worm bin, a bokashi bucket and city curbside pickup. City rules vary, so "Depends" means check your program.
Browns and greens
Every pile is the same recipe: carbon (browns), nitrogen (greens), water and air.
Browns (carbon)
Dry leaves, shredded cardboard and paper, egg cartons, straw, sawdust, wood chips.
Dry, crunchy, and the answer to most problems.
Greens (nitrogen)
Fruit and veggie scraps, coffee grounds, tea leaves, fresh grass clippings, plant trimmings.
Wet, fresh, and what makes the pile cook.
The recipe
About 2 to 3 buckets of browns for every bucket of greens. Bury fresh scraps under a few inches of browns.
Keep it as damp as a wrung-out sponge, and turn or fluff it now and then for air.
When it's done
Dark, crumbly, and it smells like a forest floor. You can't tell what went in.
A hot pile you turn often can finish in about 2 months. A pile you leave alone takes 6 to 12.
Pick a method
Backyard pile or bin
The classic. A pile around 3 feet on every side gets hot enough to break things down fast. Smaller piles still work, just slower.
Best for: yards, leaves, lots of scraps.
Tumbler
A barrel you spin instead of turning with a fork. Tidy and critter-proof, but it can get soggy, so add extra browns.
Best for: small yards, people who hate pitchforks.
Worm bin
Red wigglers in a bin of damp shredded paper eat your scraps and leave castings, the best soil there is. Fits under a sink.
Best for: apartments, and anyone who wants pets that work for free.
Bokashi
A sealed bucket and a sprinkle of bran ferment your scraps, meat and dairy included. Bury the result or add it to a pile to finish.
Best for: small kitchens and meat eaters.
Curbside or drop-off
Many cities pick up food scraps or run drop-off bins. Their facilities run hot, so they take things a home pile can't, like meat, dairy and greasy pizza boxes.
Best for: zero effort. Check your city's list.
No yard? No problem.
Keep a container of scraps in the freezer (no smell, no flies) and drop it off once a week at a community garden or drop-off site.
Best for: everyone who said "but I live in an apartment."
Troubleshooting
Nine times out of ten the answer is: add more browns.
It smells like rotten eggs, or a dumpster
Too wet and not enough air, so the wrong microbes took over. Turn or fluff it and mix in a big helping of dry browns. It'll calm down in a few days.
It smells like ammonia
Too many greens. Add browns and mix them in. Shredded cardboard works great.
It's slimy, gray and soggy
Same fix as the smell: browns and air. Leave the lid off on a dry day, or cover the pile if it's been raining.
It won't heat up
The pile is too small, too dry, or short on greens. Aim for about 3 feet on every side, water it to wrung-out-sponge damp, and add fresh scraps or grass. A cold pile still composts. It just takes longer.
It's bone dry and nothing's happening
Water it while you turn it, so the middle gets wet too. Squeeze a handful: you want a drop or two, not a stream.
Fruit flies everywhere
Bury fresh scraps under a few inches of browns, and keep a lid on the kitchen bin. Freezing scraps before they go out stops flies cold.
Rats, raccoons or other visitors
Keep meat, dairy and oily food out of home piles, and bury scraps in the middle. Use a closed bin with 1/4-inch hardware cloth underneath.
My worms are trying to escape
Usually too wet, too acidic, or too much food at once. Add dry shredded paper, ease off citrus and onions, and feed smaller amounts.
It's winter and the pile is frozen solid
Keep adding scraps anyway. Freezing and thawing breaks them down, and the pile wakes up in spring. Don't bother turning a frozen pile.
Myths, busted
"No citrus or onions"
Fine in a pile. The rule comes from worm bins, where worms just don't like them much.
"Compost stinks"
A healthy pile smells like earth. Stink means it needs browns and air.
"Compostable plastic is compostable"
Not in your backyard. About 60% of "home compostable" plastics don't fully break down in home piles. Even city programs disagree on them.
"Landfills break it down anyway"
They do, into methane. Food is about a quarter of what goes to US landfills, but 58% of the methane that escapes them.
"You need a big yard"
A worm bin fits under the sink, and a freezer bag gets you to a drop-off.
"Countertop machines make compost"
Most electric "composters" dry and grind scraps. That's a head start, not finished compost. It still needs soil or a pile.
Sources: EPA Composting at Home · Cornell Waste Management Institute · EPA landfill methane · Frontiers, compostable plastics · city program guides from NYC, San Francisco, Seattle, Portland, Austin and Toronto.