How to Make Leaf Mould from Autumn Leaves

Every autumn, gardeners rake up one of the best soil improvers there is and pay the council to take it away. Fallen leaves, left damp in a heap, turn into leaf mould: a dark, crumbly, sweet-smelling material that woodland soils are made of. It holds moisture like a sponge, improves the structure of any soil, and costs precisely nothing. Better still, making it is the laziest job in gardening — nature does all the work, and this is the month to start.

Leaf mould is not compost

A regular compost heap is driven by bacteria: it runs hot, works fast, and needs a balanced mix of green and brown material. Leaf mould is different — autumn leaves are low in nitrogen and high in tough carbon, so they are broken down slowly and coolly, mostly by fungi. That's why leaves in a compost heap seem to sit there forever, and why they get their own separate pile. The trade-off for the wait is a wonderfully fine, dark material that money can barely buy.

Method 1: the bin-bag method (small gardens)

• Collect leaves — ideally just after rain, or give dry ones a soak with the hose.
• Stuff them into black bin bags or old compost bags, pressing them down as you go.
• Stab a few holes in the sides and base with a garden fork for airflow and drainage.
• Tie the tops loosely and tuck the bags behind the shed or in any shady corner.
• Check once or twice over the year — if the leaves feel dry, pour in some water. That's the entire job.

Method 2: a leaf cage (bigger gardens)

If you have the space and the leaves, hammer four posts into a shady corner and staple chicken wire around them to make an open-topped cage about a metre square. Pile the leaves in, firm them down, water the heap in dry spells, and let it sink — a full cage shrinks dramatically as the fungi work. An open heap in a quiet corner works too; the cage just stops the wind redistributing your work across the lawn.

Tip: run the lawnmower over leaves on the grass before collecting them. Shredded leaves rot down in half the time, the grass clippings mixed in add a little nitrogen that speeds things further, and one mower pass collects the lot into the grass box for you.

Which leaves make the best leaf mould?

• Fast and fine: oak, beech and hornbeam are the classics — thin leaves, beautiful leaf mould.
• Slower but fine once shredded: sycamore, horse chestnut, sweet chestnut, plane and walnut — thick leaves that benefit from a pass with the mower.
• Pine needles: rot very slowly (two to three years) and make an acidic leaf mould that blueberries, rhododendrons and camellias love. Keep them in their own bag.
• Avoid: evergreen leaves like holly, laurel and conifer clippings (shred them for the compost heap instead), and leaves collected from busy roadsides, which can carry pollutants.

The waiting, and what you get

After about a year, you'll have a rough, crumbly mulch — leaves still recognisable at the edges but dark and half-vanished in the middle. After two years, it becomes proper leaf mould: fine, dark, and crumbly, ready for the fancier jobs. Patience is the only ingredient, and next year's batch starts while this year's finishes, so after the second autumn you'll have a continuous yearly supply.

How to use it

• One-year leaf mould: mulch beds and borders 5 cm deep, spread it around trees and shrubs, use it to earth up and protect borderline-hardy perennials, or dig it into heavy soil to open it up.
• Two-year leaf mould: sieve it and mix with garden compost and sharp sand for a homemade seed and potting mix, top-dress containers and lawns, or work it into planting holes.
• Any age: it's a soil conditioner rather than a fertiliser — it improves structure and moisture-holding rather than adding many nutrients, so it's near-impossible to overdo.

Warning: leave some leaves where they lie. A layer under hedges and in quiet corners shelters overwintering hedgehogs, frogs, toads and beneficial insects, and worms will pull leaves on the beds down into the soil for you. Rake the lawn and paths — frost-slicked wet leaves on paving are genuinely dangerous — but the wild corners of the garden want their duvet. And when you open a bag of finished leaf mould, avoid breathing in the dust and spores.

Not sure which tree your leaves fell from, and whether they're the fast-rotting kind? Photograph a leaf with PlantMe — the app identifies the tree in seconds, so you know whether you're holding oak gold or plane-tree leather.