The quick answer
- Food scraps, grass and leaves break down fastest, with half of their carbon gone in roughly two to four years, according to the decay rates EPA uses in its landfill models.
- Paper, cardboard and wood take decades. EPA’s figures put half-breakdown of copy paper at about 17 years, cardboard at about 23 and tree branches at about 35.
- Plastic, glass and metal are not food for landfill microbes, so for practical purposes they stay buried more or less as they are.
- Landfills are built to keep trash dry and sealed, which protects groundwater but also slows decay, so buried trash can last far longer than the same item in a compost pile or a field.
Why trash breaks down so slowly in a landfill
Things rot when bacteria and fungi can reach them with enough water, warmth and, for the fastest kind of decay, oxygen. A modern landfill takes most of that away on purpose. Trash is crushed tight by heavy compactors, and under 40 CFR Part 258 the operator has to spread six inches of earth, or a substitute the state approves, over it when each operating day ends. Liners below and a cap on top keep rain out and keep the liquid that does form, called leachate, from reaching groundwater.
Those steps do their job of controlling pests, odor, litter and pollution, but they also leave buried waste dark, packed and fairly dry. EPA explains that fresh trash goes through a short stage with oxygen, and that oxygen is usually used up within a year. After that, slower microbes that live without oxygen take over. Water seems to be the biggest lever: archaeologists who dug into landfills reported a clear link between how much moisture a layer held and how far its refuse had decomposed.
How long common materials take
EPA’s Waste Reduction Model assigns each organic material a decay rate for landfill conditions. Its 2023 report on food waste lists how many years it takes for half of a material’s carbon to break down into landfill gas:
- Grass clippings: about 1.8 years
- Leaves: about 3.2 years
- Food waste: about 3.6 years
- Dimensional lumber: about 6.3 years
- Copy paper: about 17 years
- Cardboard: about 23 years
- Branches: about 35 years
Keep in mind that half-life is not the finish line. Decay of this kind slows as it goes, so the second half takes as long as the first, then the remaining quarter takes as long again. EPA also notes that real rates swing with temperature, rainfall, how the landfill is run and the type of waste, so a dry desert landfill will be slower than a wet one in the Southeast.
Plastics, glass, ceramics, metal, rubber and concrete are not on that list because landfill microbes do not meaningfully digest them. You will see charts claiming a plastic bottle lasts a set number of centuries. Those are rough estimates, not measured landfill results, and nobody has watched a bottle in a landfill for that long. The honest answer is that these materials stay put for a very long time.
What landfill digs have found
The best real-world evidence comes from the Garbage Project, led by University of Arizona archaeologist William Rathje, which drilled and excavated landfills from California to Florida and sorted refuse dropped there between 1952 and 1988. The team recovered more than 2,400 newspapers that could still be dated and read, some buried 15 to 40 years. Paper made up 40 percent or more of the space in every landfill they studied, except at the very bottom of New York’s old Fresh Kills site, which sat in an unlined tidal swamp where water had broken older layers down.
The project’s reports and interviews also describe recognizable hot dogs, heads of lettuce and a bowl of guacamole, dated by a newspaper beside it to 1967. Rathje’s conclusion was that much landfill trash is closer to mummified than composted. His team did find that a large share of raw food and yard waste does break down within about the first 15 years, and that it is the main source of landfill methane.
What happens to buried trash over time
- The first days to months: trapped air lets oxygen-loving microbes start on food and yard waste. This stage gives off heat and carbon dioxide.
- Within about a year: the oxygen runs out and bacteria that work without it start producing acids, then methane.
- The next several years: food, grass and leaves do most of their breaking down, and gas production climbs. EPA notes that food waste decays so quickly that much of its methane is released before gas collection systems are installed or expanded.
- Decades: paper, cardboard and wood keep breaking down slowly, while plastics, glass and metal sit largely unchanged. Owners must keep monitoring gas and groundwater after a landfill closes; see what happens when a landfill is full.
Decomposition, methane and smell
When organic trash rots without oxygen it makes landfill gas, which EPA says is about 50 percent methane and 50 percent carbon dioxide. Municipal landfills are the third-largest human-caused source of methane in the U.S. EPA estimates that food waste, about 24 percent of what goes into these landfills, is responsible for about 58 percent of the methane that escapes from them. Many landfills collect the gas to burn it off or make power, and the rotting process is also behind most landfill odor, covered in why landfills smell.
Biodegradable labels and other myths
- “Biodegradable” does not mean it will vanish in a landfill. The label usually reflects lab or compost conditions with air, moisture and heat. Packed in a landfill, a biodegradable bag can last for years, and if it does break down it adds to methane.
- Compostable items need a compost facility. They are meant for commercial composting or a well-managed home pile, not the trash can.
- Burning trash at home is not a fix. Backyard burning creates smoke and ash and is banned in many areas. Large-scale burning happens at plants built for it; see what a waste-to-energy plant does.
- Old landfills are not empty underneath. Even decades after closing, a landfill still holds most of its plastic, glass, metal and much of its paper.
What you can do with what you throw out
Since food and yard waste break down fastest and drive most landfill methane, keeping them out of the bag makes the biggest difference. Many counties run brush and leaf drop-offs or compost sites, and our yard waste guide explains the options. Clean paper, cardboard, cans and bottles belong in recycling, where a materials recovery facility sorts them for reuse. For anything left over, use the Dumpmapper map to locate the nearest landfill or transfer station, or try our dump near me finder, and check what you can take to the dump before you load up.
Landfill decomposition FAQ
Does trash ever fully decompose in a landfill?
Food, grass and leaves largely break down over years, and paper and wood over decades, but plastic, glass and metal do not meaningfully decompose. Dry conditions can preserve paper for a very long time.
How long does food take to decompose in a landfill?
EPA's landfill model uses a decay rate at which half of the carbon in food waste breaks down in about 3.6 years. The pace keeps slowing after that and depends on moisture and temperature.
How long does paper take to decompose in a landfill?
EPA's figures put half-breakdown of copy paper at about 17 years and cardboard at about 23. Landfill digs have pulled out readable newspapers that were buried for decades.
Why don't things decompose in landfills?
Trash is compacted, covered with soil every working day and sealed with liners and caps, which keeps out much of the oxygen and water that microbes need to work quickly.
Does plastic decompose in a landfill?
Not in any meaningful way. Landfill microbes do not digest common plastics, so they stay buried. Charts giving an exact number of centuries are estimates, not measurements.
Is it bad to throw food waste in the trash?
In a landfill it rots quickly and makes methane. EPA estimates landfilled food waste causes about 58 percent of the methane that escapes from municipal landfills, so composting or food scrap programs help.
The bottom line
How long trash takes to decompose in a landfill depends on what it is. Food and yard waste do most of their breaking down within a few years, paper and wood take decades, and plastic, glass and metal stay for what is effectively forever on a human timescale. Landfills are designed to contain waste safely, not to compost it, so the best way to cut what lasts is to recycle, compost and buy less of what you will end up throwing away.