Composting does not stop in winter, but it slows down a lot, and gardeners who expect the same speed as summer are usually disappointed. The organisms that break down garden waste — bacteria, fungi and worms — need warmth, air, moisture and food, and winter takes away the warmth. A heap that turned into finished compost in two or three months in summer may take six months or more over winter, and a heap in a cold zone may freeze solid and stop altogether until spring. That is normal, and it is not a failure. This guide explains how winter composting really works, what to keep adding, what to stop adding, and how to set the heap up so it restarts quickly when the weather warms.
The honest starting point is this: cold compost slows, and in zones 1 to 4 it may stop entirely for weeks at a time. Microbial activity drops sharply as temperatures fall, and worms retreat deep into the soil or into the centre of the heap. A small heap loses heat fast and will go cold. A large heap — at least a cubic metre — holds heat better and may keep working in the middle even when the outside is frozen. None of this means you should stop composting in winter. It means you should adjust your expectations, keep feeding the heap, and let the cold do some of the work for you: freezing and thawing breaks down tough material such as stems and leaves, so it rots faster once warmth returns.
How a compost heap behaves in winter
In autumn the heap is usually at its best: warm, active, full of leaves and spent crops. As temperatures fall, activity in the outer layers stops first, while the centre may stay warm for weeks if the heap is large and well built. Turning the heap in cold weather lets the heat out, so winter turning should be less frequent than summer turning — once a month at most, and not at all in the coldest weeks. If you turn a warm heap on a freezing day, you can lose the heat it took weeks to build, and the heap may not recover it until spring.
Moisture is the other winter problem. Rain and snow keep the heap wet, and a wet heap goes airless and smelly, because water fills the air spaces that organisms need. A lid, a cover of old carpet or a sheet of plastic weighted down over the heap keeps the worst of the rain off while still letting some air in. The heap should be damp like a wrung-out sponge: if you squeeze a handful and water runs out, it is too wet, and you need to add dry browns and turn it lightly. If it is dry and dusty, which is rarer in winter but happens under a good cover, water it. Our composting basics guide explains the underlying process, and the compost ratio guide covers the green-to-brown balance that matters in every season.
What to add in winter
Keep adding to the heap all winter. Kitchen scraps — peelings, cores, coffee grounds, eggshells — are the main winter input, because there is little garden waste. Add them in the centre of the heap, under a layer of browns, so they are insulated and do not attract rats. Autumn leaves are the great winter brown: shred them if you can, and stockpile bags of dry leaves to add through winter, because dry browns are scarce once everything is wet. Shredded cardboard and newspaper are also useful winter browns, and they help soak up excess moisture. Spent bedding from herbivore pets, wood ash in small amounts, and the contents of a cold greenhouse clear-out can all go in.
Add material in layers, as in summer, but lean a little more towards browns in winter: roughly one part green to three parts brown by volume is a good winter aim, because kitchen scraps are wet and the heap is already damp. The compost ratio calculator will work out the balance for what you have. Chop or shred material before adding it, because smaller pieces break down faster and are easier for a sluggish winter heap to handle. Do not add large woody prunings whole — they will still be there in spring. Shred them, or set them aside for a separate woody pile.
What not to add in winter
The usual exclusions still apply, and a few matter more in winter. Do not add meat, fish, dairy, fats or cooked food in quantity: a cold heap cannot break them down quickly, and they attract rats, which are hungrier and bolder in winter. Do not add dog or cat waste, which can carry pathogens. Do not add diseased plants or weeds with mature seeds unless you are sure the heap runs hot — and in winter it almost certainly does not, so keep them out and dispose of them separately. Do not add large amounts of fresh grass, which is scarce in winter anyway, or anything treated with chemicals. Ash from treated wood, glossy paper and anything with paint or preservative on it should stay out. If you are unsure about a material, leave it out and check your local extension service for advice.
Keeping the heap working
There are a few practical steps that keep a winter heap alive. First, size matters: if you have two bins, fill one and let the other mature, and keep the filling bin as full as you can, because a full heap holds heat better than a half-empty one. Second, insulate the heap: a layer of straw, old carpet or cardboard around the outside of the bin helps, and a lid on top keeps rain off and heat in. Third, site matters: a heap against a sunny wall or fence stays warmer than one in an exposed, windy corner. Fourth, add an activator when you start a new winter heap — a few spadefuls of finished compost or garden soil, or well-rotted manure, introduce the organisms that start the process. Fifth, do not turn the heap in freezing weather; wait for a mild spell, and turn gently, moving the outside material into the middle.
If the heap freezes solid, do not panic and do not try to force it. Leave it, keep adding kitchen scraps to the top under a cover of browns, and let the freeze-thaw cycles break material down. When spring comes, turn the heap properly, add fresh greens, and it will usually restart within a week or two. Our winter soil preparation guide explains how finished compost fits into the winter soil plan, and the garden tasks in January guide shows where composting sits in the midwinter calendar.
Vermicompost and indoor composting in winter
Worm composting indoors or in a sheltered spot is a useful winter alternative, because worms work well at ordinary indoor temperatures. A worm bin in a garage, shed or utility room keeps processing kitchen scraps all winter, as long as it does not freeze and does not get too hot. Feed it small amounts regularly, keep the bedding damp but not wet, and do not overfeed — uneaten food goes sour. Our vermicompost guide covers worm composting in detail. A bokashi bin is another indoor option for winter: it ferments kitchen scraps, including small amounts of cooked food, and the fermented material can then be buried in the garden or added to the compost heap in spring. Neither option replaces a garden heap, but both keep kitchen waste out of the bin through the months when the outdoor heap is slow.
Using compost in winter
There is little point spreading unfinished compost in winter, because the soil is cold and plants are not growing. Save finished compost for spring, when it can be worked into beds. But winter is a good time to use compost as a mulch on empty beds: a layer of mature compost spread over the soil protects it from rain and erosion, feeds soil life, and is ready to be worked in when spring comes. Do not use unfinished compost on beds in winter — it can still be breaking down, it may contain weed seeds that survived a cool heap, and it can temporarily use nitrogen from the soil. Our compost tea guide is a summer job; in winter, the heap itself is the priority.
Common mistakes
The most common winter mistake is expecting summer speed and concluding the heap has failed when it has only slowed down. The second is turning the heap in freezing weather and losing its heat. The third is letting the heap get sodden, because a wet heap goes airless and smelly. The fourth is adding meat, dairy or cooked food that a cold heap cannot handle, which brings rats. The fifth is adding diseased plants and seeding weeds to a heap that is not hot enough to kill them. The sixth is leaving the heap uncovered so rain soaks it all winter. And the seventh is starting winter with an empty bin — a heap needs bulk to hold heat, so build it up in autumn while material is plentiful. If you are unsure whether your heap is working or has gone wrong, check your local extension service for advice.
Frequently asked questions
Does composting stop in winter?
It slows down a lot, and in cold zones it may stop entirely for weeks if the heap freezes. That is normal. A large heap may keep working in the centre, and freeze-thaw cycles break material down so it rots faster when warmth returns. Keep adding material and the heap will restart in spring.
Should I keep adding kitchen scraps in winter?
Yes. Bury them in the centre of the heap under a layer of dry browns, so they are insulated and do not attract rats. Keep the heap covered so rain does not soak it, and lean a little more towards browns than in summer.
Should I turn my compost heap in winter?
Only on a mild day, and less often than in summer — once a month at most. Turning in freezing weather lets the heat out and the heap may not recover it until spring. If the heap is frozen solid, leave it alone.
Can I use compost in winter?
Use only finished, mature compost, as a mulch on empty beds or saved for spring. Do not spread unfinished compost: it can still be breaking down, may contain surviving weed seeds, and can temporarily take nitrogen from the soil.
What is the best winter brown for compost?
Shredded autumn leaves are the best winter brown: free, plentiful and easy to stockpile in bags. Shredded cardboard and newspaper are also useful, and they help soak up excess moisture in a wet heap.