Making Leaf Mould for Free Garden Compost

Why leaf mould is the cheapest compost you will ever make

Every autumn, trees hand you a free soil improver, and most gardeners either burn it, bin it or bag it up for the council. Leaf mould is different from garden compost: it is made almost entirely by fungi, it is low in nutrients, and that is exactly why it is so useful. It will not burn plant roots or push soft, sappy growth late in the season. What it does is open up heavy clay, help sandy soil hold water, and give you a crumbly, dark material that seedlings and potted plants adore.

You do not need a big garden or a proper three-bay composting system. A strip of ground behind a potting shed, a shaded corner next to the water butt, or the back edge of an allotment plot is plenty. If anything, leaf mould suits small spaces better than a hot compost heap, because it needs nothing from you except damp and time.

Sort your leaves before you start

Not all leaves rot at the same speed, and knowing the difference saves a lot of disappointment.

• Quick (about 12 months): sycamore, lime, ash, willow, horse chestnut and poplar. These break down into decent mulch within a year.
• Slow but worth it (18 months to two years): oak, beech and hornbeam. They take longer but produce the finest, most crumbly leaf mould of all.
• Very slow: conifer and evergreen prunings, holly and laurel. They are acidic and waxy, so keep them in a separate bag and use the result around blueberries, rhododendrons and camellias.
• Leave alone: leaves from the gutter of a busy road, or anything mixed with dog mess or pernicious weed roots such as bindweed or ground elder.

A mix is fine. If you have oak and sycamore together, the sycamore will rot first and you can sieve it out as you go.

Bag it, cage it or stack it

The classic small-space method is the black bin bag. Fill it loosely, punch six to eight holes in the base and sides with a fork, give it a splash of water if the leaves are dry, then tie the top loosely rather than sealing it tight. Tuck the bags behind the shed, under a bench or along a north-facing wall. Woven builder's sacks and old compost bags turned inside out work just as well and look tidier.

On an allotment, a wire cage is hard to beat. Drive four stakes into the ground in a square about a metre across, wrap chicken wire around them, and line the sides with cardboard. Fill it with leaves, firm them down gently as you go, and water the pile if we get a dry spell. When it has slumped to about half its original volume, shovel it into bags to finish. A bin made from four pallets wired together does the same job and gives you somewhere to lean your tools.

Aim for the dampness of a wrung-out sponge. Too dry and nothing happens; too wet and it turns to slime. If it smells sour, fork it over and mix in some shredded cardboard.

Speeding things along

You cannot rush nature, but you can nudge it:

• Run the mower over the leaves before bagging. Shredded leaves rot in roughly half the time.
• Mix in a thin layer of grass clippings or a couple of handfuls of old leaf mould as a starter.
• Sprinkle in a little garden soil to introduce more fungi.
• Keep the bags or cage out of full sun so they stay consistently moist.
• Turn a wire cage once or twice a year with a fork. Bags can simply be rolled over.

Label everything with the month and year in marker pen. Memory is unreliable, and there is nothing worse than opening a bag of half-rotted leaves in spring when you wanted mulch.

Using your leaf mould

After a year you will have a coarse, usable mulch. Spread a 5cm layer around soft fruit, rhubarb, raspberries, perennials and fruit trees in autumn or early spring, keeping it clear of stems. It suppresses weeds and holds moisture without feeding lush growth.

After two years, sieve it and you have something special. Use it as a seed-sowing mix on its own, or blend one part sieved leaf mould with one part garden compost and two parts loam or topsoil for containers, raised beds and potting on. It is also excellent brushed into a lawn as an autumn top dressing, and it makes a lovely dark top layer for pots on a shed windowsill or outside a greenhouse door.

Store finished mould in bags inside the shed or under a tarpaulin, and keep it just damp. It will sit happily for a year or more, ready whenever you need it.