Compost not breaking down? Match what you see inside the bin

Compost bin not breaking down? What's inside tells you why: too dry, too wet, too chunky or short of greens. Match it and make one or two changes.

Linocut print of a plastic compost bin with its lid off and a fork lifting barely rotted leaves and peelings.
What you find in the middle of the bin tells you what to change.

If your compost is not breaking down, you’ve probably met the usual answer already, a list of five causes with no way to tell which one is yours. Whether it’s “not rotting” or has just stalled, a bin or pile that stops is a common fault, not proof you’re bad at composting.

Quick fix

Check before you change anything.

  1. Tumbler, or the middle of winter? Start there instead. A drum has its own usual causes, covered in Compost tumbler problems, and in winter a quiet bin is mostly resting, as Composting through winter explains.
  2. Dig into the middle. The top is often drier, wetter or fresher than the rest, so it can mislead you.
  3. Squeeze a handful. It should feel like a wrung-out sponge. If it falls apart and feels dry, it’s too dry. If water runs out, it’s too wet.
  4. Look for whole pieces. Cardboard, leaves or sticks still in one piece? See whole pieces.
  5. Squeeze feels right? Check the bottom. Open the hatch at the base, or dig down.
    • If it’s dark and crumbly, or the bin is under about six months old, it’s just slow.
    • If the bin is older and the bottom looks no different from last time, it’s probably short of greens.

Dry, and it looks the same as last month

A squeezed handful falls apart, the inside feels dry and fibrous, and the scraps look much as they did when they went in. The organisms that do the work need moisture, and without it they stop.

Water it in layers as you turn it, a little at a time, and recheck with the squeeze. Pouring water over the top doesn’t work, because a dry pile sheds it. Mix in a bucket of fresh greens as you go, too. The UK’s Royal Horticultural Society (RHS) links a dry, fibrous pile to too little moisture and too many browns.

For how to rewet it properly, and why size and shade matter, see Compost too dry.

Wet like mud or slimy

Water runs out when you squeeze, and the inside is dense, slimy and maybe sour. One gardener on a permies.com thread described theirs as “cold brown mush throughout”. Water has filled the gaps where air should be, and the organisms that need air stop working.

Mix dry browns (torn cardboard, dry leaves, straw) through it as you turn it, a bucket or two at a time. Then cover the bin or pile so rain stops adding to the problem.

For step-by-step drying, and how long it takes, see Compost too wet. In a closed plastic cone bin (a “dalek” in the UK), the wet lump usually sits at the bottom: see Plastic cone compost bin not working?.

Cardboard, leaves or sticks still in one piece

The rest is rotting, but sheets of cardboard, whole leaves or twigs are still easy to recognize. Big, tough pieces give the organisms little surface to work on. Leaves are slow by nature, too. The RHS says most take about two years on their own, and thick ones like sycamore and horse chestnut need shredding.

  • Tear or shred cardboard, and leave out waxed or chemically coated cardboard, because the coating doesn’t break down. Shred stems, prunings and thick leaves too, or give a big leaf fall its own pile.
  • Put anything still whole back in for the next round when you empty the bin.

If the cardboard is dry and stiff, do the middle squeeze from the Quick fix. If that falls apart dry too, the whole bin is dry, so see Compost too dry.

Damp and sweet-smelling, but not changing

The squeeze feels right, it smells pleasant, and the bottom isn’t changing. Nothing looks wrong, which is why this one is easy to miss. Feeling cool isn’t the fault on its own, because a home bin can work for months without ever feeling warm.

Cornell’s troubleshooting table describes a damp, sweet-smelling pile that “will not heat up” and puts it down to too little nitrogen, and other US university gardening guides say the same. In browns-and-greens terms, that means too few greens.

Mix in a bucket or two of fresh greens as you turn it. Vegetable peelings and coffee grounds both work, and so do grass clippings in a thin layer rather than a thick mat.

For what counts as a green, and the rough balance to aim for, see Browns and greens.

Dark and crumbly at the bottom: just slow

Home compost is slow. The RHS gives six months to two years for it to mature, and Cheshire East Council in the UK says up to a year in a home bin, longer in cold weather. If every source seems to give a different timeline, that’s because bins differ, not because you’ve done it wrong.

A working bin is dark and crumbly at the bottom and smells like damp woodland, with recognizable scraps on top, even if it never feels warm. A bin only a few months old may not have reached that point yet, either. Neither bin is stalled.

To keep it moving, fork it through every few months, as the RHS suggests, and keep the mix right. Browns and greens has the balance.

If that didn’t work