Making Leaf Mould for Free Garden Compost

Why Leaf Mould Deserves a Corner of Your Garden

Every autumn, Britain's streets and gardens are buried under a free harvest that most people rake up and bin. Oak, beech, sycamore, horse chestnut — tonnes of it, all quietly carted away. If you have a single mature tree within a hundred yards of your plot, you have the raw material for one of the finest soil improvers money can't easily buy.

Leaf mould is what happens when fallen leaves rot down slowly, mostly through the action of fungi rather than the heat-loving bacteria that drive a traditional compost heap. The result, after a year or so, is a dark, crumbly, sweet-smelling material that looks a little like coffee grounds and behaves like a gentle, slow-release mulch. It holds water, improves soil structure and feeds the soil life that feeds your plants.

Best of all, it costs nothing but a bit of patience.

Which Leaves Are Worth Collecting

Not all leaves rot at the same speed. Thick, leathery leaves take far longer to break down, and some are best kept out of the mix altogether.

• The good stuff: oak, beech, hornbeam, lime and most deciduous leaves break down reliably within a year.
• Slower customers: sycamore, horse chestnut and walnut can take two years. Perfectly usable, just be prepared to wait.
• Best avoided: conifer needles and evergreen leaves such as holly and laurel. They are acidic, waxy and slow, though a small quantity mixed in will do no real harm.
• Never use: leaves from diseased trees, or anything raked up with a lot of ivy, weeds or litter attached.

The Bin Bag Method

This is the simplest approach going, and it works in the smallest garden.

• Collect dry-ish leaves on a dry day. Wet leaves are heavy and prone to going slimy.
• Fill black bin bags or old compost sacks loosely — no need to cram them solid.
• Punch six to eight holes in each bag with a garden fork or scissors, so air and rain can get in and excess moisture can drain.
• Add a handful of garden soil, or a sprinkling of water if the leaves are bone dry. Moist, not soaked, is the target.
• Tie the tops loosely so air still moves, then stack the bags behind a shed, under a hedge or in a quiet corner.
• Leave them for twelve months. Check once or twice, and give the bags a shake if you remember.

After a year, the contents should have collapsed into crumbly dark material. If it is still recognisably leaves, give it another six months.

Making It Faster, and What to Do While You Wait

A year is the going rate, but a few tricks hurry things along. Chopping leaves with a mower before bagging them increases the surface area and can shave months off the process. Mixing in grass clippings adds nitrogen and speeds decomposition, though keep the ratio low — too much grass and the bags turn anaerobic and smelly. Turning the heap, or simply shaking the bags every few months, also helps.

If you have the space, a wire mesh bin works beautifully. Hammer four stakes into the ground in a square, wrap chicken wire around them, and tip the leaves in. It looks tidier than a pile of bags and rots a little faster because air reaches it from all sides.

While you wait, remember that a thin layer of whole leaves spread directly on borders over winter does a fine job as a mulch in its own right. Worms will pull them down into the soil by spring.

How to Use the Finished Stuff

Once your leaf mould is dark and crumbly, it earns its keep in several ways.

• As a mulch: spread a 5-8cm layer around shrubs, perennials and fruit bushes to suppress weeds and hold moisture.
• As a soil improver: fork it into beds to lighten heavy clay and add body to sandy soil.
• In seed and potting mixes: sieve it and blend with garden compost and grit for a fine, free seed-sowing medium.
• As a lawn dressing: a light scattering brushed into the grass in autumn feeds the turf and improves the soil underneath.

It is gentle enough to use neat, unlike richer composts, so you needn't worry about burning young plants.

A Few Troubleshooting Notes

If the bags smell sour and slimy, they have gone anaerobic — empty them out, mix in some dry leaves or shredded cardboard, and start again in a fresh bag with more holes. If nothing seems to be happening at all, the leaves are probably too dry; a good soaking will set things right. And if you find the odd bag that has turned into a solid, matted lump, break it up and give it another few months.

The great pleasure of leaf mould is that it asks so little of you. A couple of hours raking on an autumn afternoon, a few bin bags and a forgotten corner of the garden — and next year you have a barrowload of the best mulch you cannot buy. Once you have made your own, you will never look at a drift of fallen leaves the same way again.