Fall is the biggest composting season of the year. The garden produces a glut of material all at once: fallen leaves by the barrowload, spent annuals and vegetable plants, prunings, grass clippings from the last cuts, and kitchen waste that keeps coming whatever the season. Handled well, that glut becomes next year's soil improver. Handled badly, it becomes a soggy, smelly heap that sits untouched until spring. Fall composting is about managing volume, getting the balance right, and setting the heap up so it keeps working, slowly, through the cold months.
The good news is that fall gives you the two things compost needs most: plenty of carbon-rich browns in the form of leaves, and plenty of nitrogen-rich greens in the form of spent plants and grass. The challenge is that cold weather slows the organisms that do the composting, so a heap that would finish in two months in summer may take six months or more in fall and winter. That is fine, as long as you plan for it: build the heap well in fall, tend it while the weather allows, and let it mature over winter. Our composting basics guide explains the principles, and our compost ratio calculator works out the green-to-brown balance for you. If you are unsure about composting in your area, check your local extension service.
What goes in the fall compost heap
Fall gives you more browns than any other season, and leaves are the star. Shredded leaves break down far faster than whole leaves, which mat together and exclude air, so run them over with a mower or shred them before adding them to the heap. Mix leaves with greens as you add them, rather than piling a thick layer of leaves alone, which will sit dry and do nothing. Spent annuals and vegetable plants are good greens, as long as they are healthy; chop them small so they break down faster. Grass clippings from the last mow are nitrogen-rich greens, but add them in thin layers mixed with browns, since a thick layer of grass alone goes slimy and smelly.
Prunings can go in if chopped small, though woody material breaks down slowly and is often better chipped or kept for a separate slow heap. Kitchen waste — peelings, coffee grounds, eggshells, tea bags that are plastic-free — keeps coming through fall and winter and adds valuable nitrogen. Our coffee grounds in garden and eggshells in garden guides cover two common additions. Straw, shredded cardboard and paper are useful browns when leaves run short. See our compost ratio guide for the balance to aim for: roughly one part green to two or three parts brown by volume.
What to keep out of the fall heap
Some fall material should never go in the compost heap. Diseased plants, especially those with blight, mildew or canker, should be kept out unless your heap runs genuinely hot, since a cool heap will not kill disease organisms and you will spread them when you use the compost. Our powdery mildew treatment and early blight tomatoes guides explain which diseases matter most. Weeds with mature seeds should also stay out of a cool heap, since the seeds survive and germinate when the compost is spread. Invasive weeds such as bindweed and couch grass roots should never be composted, since even small pieces can regrow.
Do not compost meat, fish, dairy, fats or cooked food in large amounts, since they attract rats and smell, and do not compost pet waste from dogs or cats, which can carry pathogens. Treated timber, glossy paper, and anything with chemicals on it should stay out too. Fallen fruit that is diseased or rotting should be disposed of rather than composted, since it harbours disease — see our brown rot fruit guide. When in doubt, leave it out: a heap that is missing one ingredient is far better than a heap contaminated with disease or weed seeds.
Leaf mould: the fall speciality
Leaf mould deserves its own pile. Unlike compost, leaf mould is made from leaves alone, rotted down slowly by fungi rather than by the hot bacterial process of a compost heap. It takes a year or two, but the result is a dark, crumbly, sweet-smelling material that is excellent for improving soil, mulching, and mixing into potting compost. It holds water well, feeds soil life, and is particularly good for woodland plants and for lightening heavy soil. Our leaf mulch guide covers leaves in the garden more broadly.
Making leaf mould is simple: collect fallen leaves, shred them if you can, pile them in a corner, in a wire bin, or in bags with holes punched in them, wet them, and leave them. The pile needs to stay damp, so water it in dry spells and cover it to keep rain off if it gets too wet. Turn it occasionally if you want it faster, or leave it alone if you are patient. After a year the leaves will have rotted into a coarse mould that is good as a mulch, and after two years it will be fine and crumbly and good as a soil improver. Start a leaf mould pile every fall and you will always have one ready, which is one of the best routines in gardening.
Hot heaps vs cool heaps in cold weather
A hot heap breaks down fast because the organisms in the middle generate heat, and a well-built heap can reach high temperatures even in fall. To get a heap hot, build it in one go rather than adding a little at a time, make it at least a cubic metre in size, get the green-to-brown balance right, keep it damp like a wrung-out sponge, and turn it every few weeks to let air in. A hot heap will steam on a cool morning and feel warm when you push your hand into the middle. Our composting basics guide explains the hot heap method in detail.
In late fall and winter, most heaps go cool, and that is normal. The organisms slow down as temperatures drop, and the heap may appear to stop altogether in the coldest weather. That is not a failure: the heap will pick up again in spring. To help a fall heap, build it in a sheltered spot, cover it to keep rain off and warmth in, and insulate it with a layer of straw or old carpet if you have it. Do not turn a frozen heap, since you will lose what little heat it has, and do not add large amounts of water in cold weather. A cool heap still produces good compost, just more slowly — six to twelve months rather than two to three — and it is perfectly good for the garden when it is ready.
Tending the heap through fall and winter
Turn the heap while the weather is still mild, moving outside material into the middle, which reintroduces air and mixes the contents. Check moisture each time: if it is dry, water it; if it is wet and smelly, add dry browns such as shredded cardboard or straw and turn it. A heap that smells like ammonia has too many greens, and a heap that smells sour is too wet and airless. Add browns and turn it in both cases. Cover the heap with a lid, tarp or old carpet to keep rain off, since a soaked heap goes anaerobic and stops working.
In winter, leave the heap largely alone. Add kitchen waste through winter, burying it in the middle of the heap where it is warmest, and cover each addition with browns. Do not expect much visible progress in the coldest months, and do not dig into a frozen heap. In spring, turn the heap, check moisture, and let it finish. Finished compost is dark, crumbly and smells like earth, and you should not be able to recognise the original materials in it. Test it with a few fast seeds such as cress: if they germinate and grow well, the compost is ready. Our vermicompost guide covers worm composting, which can run indoors through winter and is a good complement to an outdoor heap.
Using fall compost in the garden
Compost made from last year's fall heap is ready to use this fall, and it is the best time to spread it. Work a layer into beds being planted, spread it as a mulch on the surface of beds that will rest over winter, and mix it into potting compost for containers. Our fall soil preparation guide explains how to use compost on beds, and our fall mulching guide covers compost as a mulch. Use only mature compost on food beds and on seedlings, since immature compost can harm plants by temporarily using nitrogen as it continues breaking down. Wear gloves when handling compost and wash your hands before eating, and wear a mask when turning a dry heap, since compost dust can irritate lungs. If you are unsure about safe composting practice, check your local extension service.
Frequently asked questions
What leaves are best for composting?
Most fallen leaves compost well, especially when shredded. Shredding stops them matting together and speeds breakdown enormously. Mix leaves with greens as you add them rather than piling thick layers of leaves alone.
How long does fall compost take?
A hot, well-managed heap can finish in two to three months in warm weather, but a fall heap that goes cool over winter typically takes six to twelve months. That is normal, and the compost is just as good when it is ready.
Can I compost diseased plants in fall?
Not in a cool heap. Disease organisms survive cool composting and spread when the compost is used. Keep diseased material out unless your heap runs genuinely hot, and dispose of it with household waste where local rules allow.
What is leaf mould and how do I make it?
Leaf mould is leaves rotted down slowly by fungi into a dark, crumbly soil improver. Pile shredded leaves in a bin or bags with holes, keep them damp, and leave them for one to two years. It is excellent for improving soil and as a mulch.
Should I keep adding to my compost heap in winter?
Yes, kitchen waste can go in all winter. Bury it in the middle of the heap and cover it with browns. Do not expect much progress in the coldest weather, and do not turn a frozen heap. If you are unsure, check your local extension service.