Composting in Winter: How to Keep Your Bin Working

By January, the bin that felt warm to the touch back in October can look like a bucket of frozen tea leaves. Nothing seems to be happening and the contents have stopped shrinking. That is not failure. Composting is mostly the work of bacteria and fungi, helped along by worms, woodlice and other small creatures, and all of them slow down as the temperature falls. Winter composting is less about making compost quickly and more about protecting what you already have, keeping it in good condition, and giving the heap a head start when the weather turns.

Why a winter bin goes quiet

An active heap makes its own heat. Bacteria breaking down soft, green material release energy, which is why a well-built pile can feel warm in the middle even on a frosty morning. The catch is that heat is generated in the centre and lost from the edges. In summer the pile produces heat faster than it escapes. In winter it loses that race.

Once the core drops to a few degrees above freezing, the microbes doing the heavy lifting become sluggish, and worms simply move below the frost line and wait. The compost does not die, it pauses. A heap that is small, wet and exposed to wind will pause sooner and for longer than a large, sheltered one sitting against a wall.

Shelter, size and position

If your bin lives in a wind-blasted corner at the bottom of the garden, winter is a good time to reconsider it. A spot against a south- or west-facing wall, in sun for part of the day and out of the prevailing wind, will stay noticeably warmer. Grouping two bins together helps too, because they shelter one another.

Volume matters more than most people expect. A small tumbler half-full of peelings has almost no mass to hold warmth, so its temperature follows the air. A bin filled to at least three-quarters, and ideally a cubic metre or more, keeps far more of the heat it generates. If you have room, run two systems: one you are filling now, and one you leave alone to finish. The bin you leave alone is the one that will be ready first in spring.

Insulation that actually works

Insulation slows heat loss; it does not create heat. That is still worth having when night temperatures drop below zero.

• Straw bales or bags of dry leaves stacked around the sides. Cheap and effective if you have them.
• An old wool blanket or piece of carpet over the lid, weighted with a brick. Keep it dry or it will soak through and rot.
• Bubble wrap or foil-backed insulation wrapped around a plastic dalek bin and tied in place.
• A thick layer of shredded cardboard or dry leaves on top of the contents, like a duvet.
• A well-fitting lid with a weight on it, so wind cannot lift it off in a storm.

If the bin stands on cold concrete or paving, cushion the base as well. A layer of cardboard or a few centimetres of twigs and dry stems at the bottom lifts the lower contents off the cold surface. One warning: do not wrap a bin so tightly that no air can get in. Leave gaps around the base and the lid. A sealed, airless bin turns sour and slows down even further.

Turning: less often, and only when it helps

Turning aerates a heap, mixes fresh material into the warm centre and gives the whole thing a lift, which is why the usual advice is to turn every week or two. In winter that advice works against you. Every time you open a cold heap and fork it over, you release the little warmth it has held on to.

So cut back. Turn once in midwinter if you get a mild, still day, and again in late winter if the bin is full. Bring the outside edges into the middle and push the middle outwards. If the contents have gone slimy, sour-smelling or compacted into a solid block, deal with it sooner, but choose a mild day rather than the middle of a cold snap, and mix in dry browns as you work.

The winter rule is simple: if the heap is not causing a problem, leave it alone.

Getting the moisture balance right

Winter rain is the main threat. Waterlogged contents freeze into a lump, air cannot move through them, and the bin turns anaerobic. The test is the same as in summer: squeeze a handful of the contents. It should feel like a wrung-out sponge, damp but not dripping. If water runs down your wrist, it is far too wet.

The remedy is browns: shredded cardboard, torn egg boxes, newspaper, dry autumn leaves, sawdust from untreated wood only. Keep a bag of dry browns beside the bin so you can layer as you go through the winter, and check the lid for splits and gaps that let rain in.

Under a tight lid, the opposite problem can occur in a dry, cold spell. If the contents are dusty and lifeless, add water a litre at a time and mix it through. Never leave standing water on the surface. It freezes into a cap that traps smells in and keeps air out.

What to add, and what to leave out

Winter kitchen waste is wet and soft: peelings, tea bags, coffee grounds, tired salad leaves. Chop everything smaller than you would in summer. Small pieces break down faster and do not freeze into lumps.

Good winter additions

• Vegetable and fruit peelings, chopped small
• Coffee grounds, loose tea and plastic-free tea bags
• Crushed eggshells
• Shredded cardboard, paper, egg boxes and used kitchen roll
• Dead houseplants and spent flowers
• Wood ash from untreated wood, in thin sprinklings only

Better left out until spring

• Large unchopped items, which sit frozen until March
• Cooked food, meat, fish and dairy in an open heap, as they attract rats
• Diseased plants, perennial weed roots and anything treated with weedkiller
• Dog and cat faeces
• Glossy magazines and shiny wrapping paper

Keep a small lidded caddy indoors and empty it every couple of days. Scraps left in a frozen outdoor caddy stick to the sides and refuse to budge.

A five-minute winter routine

You do not need to fuss over a bin in winter. A short weekly check is enough.

1. Check the lid, weights and any insulation. Wind and rain do most of the damage.
2. Add a handful of browns every time you tip in a caddy of kitchen waste.
3. Do the squeeze test once a fortnight and adjust with browns or a little water.
4. Turn once in midwinter and once in late winter, on a mild day only.
5. Keep the indoor caddy small and empty it often.
6. If the bin is nearly full, start stockpiling shredded cardboard and dry leaves for spring.

Then step back and let it be. The first mild days of March will do more for your compost than anything you can do in January, and a bin that has been kept sheltered, damp but not wet, and reasonably full will usually heat up again within a couple of weeks of the weather turning.

Photo: Efrem Efre / Pexels