Cover your compost pile when you want to speed decomposition, keep out pests, or reduce odor — but an uncovered pile works fine if you have space and don't mind waiting longer

Whether to cover a compost pile depends on what problem you're trying to solve. A cover traps heat and moisture, which speeds up decomposition by weeks or months. It also stops raccoons, rats, and flies from getting in, and it reduces the smell that bothers neighbors. But if you have room, don't live near wildlife, and can wait six months to a year, an open pile works perfectly well. The choice comes down to your space, your neighbors, and how fast you want finished compost.

Key Takeaways

  • A cover speeds decomposition from six to twelve months down to two to four months by keeping the pile warm and moist.
  • Covers prevent raccoons, rats, and flies from nesting in or feeding on your pile, which is the main reason to use one in populated areas.
  • You can use a tarp, plywood, a commercial bin lid, or even cardboard — the material matters less than keeping the pile from drying out.
  • An uncovered pile still decomposes but takes longer and attracts more pests; it works best in rural settings with space between neighbors.
  • Covers need ventilation holes or gaps so air can still reach the center of the pile, or decomposition slows and the pile starts to smell.

Why covering speeds up decomposition

Compost breaks down fastest when three conditions are met: the right mix of materials (brown and green), moisture, and heat. A cover traps the warmth that the pile generates as microbes break down organic matter. Without a cover, that heat escapes into the air, especially on cold days or at night. The cover also prevents rain from waterlogging the pile or drought from drying it out — both slow decomposition to a crawl.

The difference in speed is real. An uncovered pile in a temperate climate typically takes nine to twelve months to become finished compost. A covered pile in the same conditions can finish in two to four months, depending on how often you turn it and how well you balance your materials. In winter, a covered pile may keep decomposing while an uncovered one nearly stops.

Covers that work against pests and smell

If you live in a neighborhood or near woods, a cover is your best defense against unwanted visitors. Raccoons and rats dig into open piles looking for food scraps. Flies lay eggs in exposed food waste. A solid cover with no gaps stops them from getting in. Even a loose cover — one that doesn't seal perfectly — deters most pests because it makes the pile harder to access than an open one.

A cover also traps odor. Decomposing food scraps release ammonia and hydrogen sulfide, especially when the pile is too wet or too dense. A cover doesn't eliminate the smell, but it contains it so neighbors downwind don't notice. This matters most if you live close to other houses or if you compost meat, fish, or dairy (which you shouldn't, but people do).

Types of covers and how to use them

You don't need to buy anything. A tarp — even a cheap plastic one — works well. Lay it over the pile and weigh down the edges with bricks, boards, or soil so wind doesn't blow it off. Leave small gaps or holes so air can reach the pile; a tarp that seals completely will suffocate the decomposition and create a stinking, anaerobic mess.

Plywood is another free or cheap option if you have scrap pieces. Lay it flat on top and weight it down the same way. Plywood lasts longer than tarp in sun and rain, but it's heavier to move when you turn the pile. Cardboard works too — it breaks down over time, which is fine because you can just add it to the pile when it falls apart.

Commercial compost bins come with fitted lids that seal tightly. These are convenient and look neat, but they're expensive and often too small for a household that generates a lot of yard waste. Wooden pallet bins with a plywood lid are a middle ground — cheap to build, sturdy, and straightforward to access.

Whatever you use, drill or cut small holes in the cover, or leave gaps at the edges. The pile needs oxygen to decompose aerobically (the fast, non-smelly way). A sealed cover turns the pile anaerobic, which slows decomposition and creates a foul smell.

When you don't need a cover

If you have space away from neighbors, live in a rural area, and don't mind waiting, skip the cover. An open pile still decomposes — it just takes longer and attracts more insects and small animals. In a dry climate, an uncovered pile may dry out too much and stop decomposing altogether; in that case, a cover helps even if pests aren't a concern.

An uncovered pile is also easier to turn and add to. You don't have to move a cover every time you want to fork in new material. If you're a casual composter and don't mind the slower timeline, the simplicity of an open pile is worth it.

Common mistakes when covering a pile

The most common mistake is sealing the cover too tightly. A completely airtight cover starves the pile of oxygen, and decomposition shifts from aerobic (fast, odorless) to anaerobic (slow, stinking). If your covered pile smells like rotten eggs or sewage, it's anaerobic. Lift the cover, poke holes in it, or leave gaps at the edges to let air in.

The second mistake is covering a pile that's too wet. If you've been adding lots of grass clippings or kitchen scraps without enough brown material (leaves, straw, shredded paper), the pile becomes soggy. A cover traps that moisture and makes it worse. Before you cover, make sure the pile feels like a wrung-out sponge — moist but not dripping.

A third mistake is forgetting to weight down the cover. Wind will blow it off, and then you're back to an uncovered pile. Use bricks, cinder blocks, soil, or boards around all four edges.

Covering a pile in different seasons

In spring and summer, a cover helps prevent the pile from drying out in heat and sun. It also keeps flies and other insects at bay during the season when they're most active. If you live somewhere hot and dry, a cover is almost essential.

In fall and winter, a cover traps the heat the pile generates, which keeps decomposition going when outdoor temperatures drop. Without a cover, a pile in a cold climate may nearly stop decomposing from November through March. A cover can keep it active all year.

In wet climates, a cover prevents the pile from becoming waterlogged during heavy rain. Too much water drives out air and creates anaerobic conditions. A sloped or peaked cover sheds water instead of letting it pool on top.

Frequently Asked Questions

Can I use a black plastic tarp to heat up my pile faster?

Yes. Black plastic absorbs sunlight and raises the temperature inside the pile, which speeds decomposition. It also traps moisture better than clear plastic. The downside is that black plastic degrades in sunlight and becomes brittle after a year or two, so you'll need to replace it more often than a thicker material like plywood.

What if my cover blows off in the wind?

Weight it down with bricks, boards, cinder blocks, or soil around all four edges. If wind is a constant problem, build a frame from wood or PVC pipe and attach the cover to the frame so it can't shift. Alternatively, use a commercial bin with a fitted lid that locks in place.

Do I need to remove the cover to turn the pile?

Yes, you'll need to move it to access the pile. If you turn your pile often (every week or two), an uncovered pile or one with a removable lid is more convenient than a heavy plywood cover. If you turn it rarely or not at all, a cover is less of a hassle.

Can I compost in winter if I cover the pile?

Yes, a cover helps. The pile generates its own heat as microbes work, and a cover traps it. In very cold climates, decomposition slows dramatically, but it doesn't stop. A covered pile will finish faster than an uncovered one, even in winter.

What happens if I cover a pile with meat or fish scraps?

A cover will contain the smell, but it won't stop pests from trying to get in. Meat and fish attract rats and raccoons strongly, and they'll dig or claw at a tarp. The best approach is not to compost meat or fish at all — they're slow to break down and create odor problems. If you do, bury them deep in the center of the pile and cover it with a sturdy lid or bin, not just a tarp.