Composting basics
Last reviewed September 2026 · written from public-domain USDA/NOAA data and Cooperative Extension references — see how we source data
Compost is the cheapest soil improvement there is and turns kitchen and garden waste into the one amendment nearly every garden wants more of.
Greens and browns
Aim for roughly equal volumes of "greens" (nitrogen-rich: vegetable scraps, coffee grounds, fresh grass clippings, spent plants) and "browns" (carbon-rich: dry leaves, straw, cardboard, wood chips). Too many greens turn slimy and smell; too many browns just sit there.
Chop or shred material and keep the pile about as damp as a wrung-out sponge.
Greens and browns: carbon-to-nitrogen ratio
Choosing a bin
An open pile or a simple three-bay wooden bin is cheapest and handles the most material: fill one bay, turn it into the next, and use the third for finished compost. Enclosed plastic bins keep things tidy and deter animals but are slower to turn.
Tumblers are easy to turn but only finish a batch if you stop adding to it. For a flat or balcony, a worm bin turns kitchen scraps into rich worm castings in a small box indoors.
Keep out
Meat, dairy, oil and cooked food (pests and smell in most home systems), pet waste, diseased plants, weeds gone to seed, and anything treated with persistent herbicide — including some straw and manures, which can damage a garden for years.
Hot vs cold
A hot pile — at least a cubic yard, balanced, turned every week or two — reaches 130–150°F, kills most weed seeds and pathogens, and finishes in one to three months. A cold pile is just a heap you add to and ignore; it works in 6–12 months and does not kill weed seeds.
Using it
Finished compost is dark, crumbly and smells like forest floor, with no recognizable food. Spread an inch or two on beds once or twice a year, use it as a quarter to a third of a raised-bed mix, or brew none of it into "tea" — just dig it in. The compost calculator works out how much a bed needs.
Troubleshooting a pile
Smells of ammonia: too many greens. Mix in dry leaves, straw or shredded cardboard.
Slimy and rotten-smelling: too wet and airless. Turn it and add dry browns.
Not heating up: too small, too dry or too much brown material. Build it to at least a cubic yard, water it as you turn, and add fresh greens such as grass clippings.
Fruit flies or animals: bury fresh scraps in the middle of the pile under a layer of browns, and keep meat and cooked food out.
How much you can make
A household with a garden typically makes a few cubic feet of finished compost a year from kitchen scraps and garden waste, because material shrinks by half or more as it breaks down. Collecting fall leaves - yours and the neighbors' - is the easiest way to make much more.
Common questions
How long does compost take to make?
A hot, well-balanced pile turned every week or two can finish in one to three months. A cold pile that you just keep adding to takes six to twelve months or more. Chopping material small and keeping it damp speeds up either kind.
Can I compost in winter?
Yes, but it slows almost to a stop in cold weather. Keep adding scraps - they will break down when it warms up in spring. A large pile or an insulated bin keeps working longer into the cold.
Can you add too much compost to a garden?
Over years, yes. Heavy annual applications, especially of manure-based compost, can build up phosphorus and salts. An inch or two a year on vegetable beds is plenty; the compost calculator works out how much that is.
Do I need a compost activator?
No. The microbes that do the work are already on the plant material. A shovel of finished compost or garden soil mixed into a new pile is all the "starter" it needs.