How to Make Leaf Mould for Free Compost

Why Leaf Mould Deserves a Place in Every Garden

Come October, most of us look at the lawn and see nothing but a chore. A carpet of sycamore, oak and beech leaves that smothers the grass, clogs the gutters and has to be cleared before it turns to slime. But those same leaves are one of the finest free resources a gardener can lay hands on. Given a year or two, they rot down into leaf mould — a dark, crumbly, sweet-smelling soil conditioner that will do things no bag of shop-bought compost quite manages.

Leaf mould is not a fertiliser in the usual sense. It is low in nutrients, but that is precisely its strength. It is a soil conditioner, not a feed. Dig it into heavy clay and it opens the structure, letting air and water move. Spread it on sandy ground and it holds moisture where before it ran straight through. Use it as a mulch, a seed-sowing mix ingredient, or a top dressing for woodland plants, and you will see the difference within a season.

What to Collect, and What to Leave Alone

Not all leaves are equal. The best leaf mould comes from leaves that break down reasonably quickly and are low in tannins and lignin.

• Ideal: oak, beech, hornbeam, field maple, hazel, lime and most fruit tree leaves. These rot into a lovely friable mould in twelve to eighteen months.
• Slower: sycamore, horse chestnut and sweet chestnut take longer and are best mixed with faster material.
• Avoid: evergreen leaves such as holly, laurel and conifer needles. They are waxy and acidic and can take three years or more. Keep them in a separate bin if you have the space — conifer mould is excellent for rhododendrons and blueberries once it finally matures.

Never collect from roadsides where leaves may be contaminated with oil and heavy metals, and avoid leaves from trees showing signs of disease. Horse chestnut with bleeding canker, for example, is best left where the council can deal with it.

Bags, Bins and the Black Bin Liner Trick

You do not need a fancy compost system. The traditional method is the simplest and still the best.

Take a black plastic bin liner, punch a good dozen holes in the sides and base with a garden fork, stuff it full of damp leaves, tie the top loosely, and tuck it behind the shed. That is genuinely all there is to it. The holes let air in and excess water out, the black plastic warms in the sun, and the fungal action gets to work. Leave it for a year and you will open it to find a crumbly brown material at the bottom and recognisable leaves at the top. Give it another year and the whole bag will be ready.

If you prefer something tidier, a wire mesh bin about a metre square is ideal. Fill it, tread the leaves down, water them if they are dry, and cover with an old piece of carpet or a tarpaulin to keep them moist and dark. Turn the heap once or twice if you have the energy, but honestly, leaf mould is forgiving. Neglect it and it still works.

A word on quantity: one cubic metre of loosely packed leaves will give you roughly a wheelbarrow of finished mould. If you have a decent-sized garden, aim for several bags. You will be glad of them.

Speed It Up Without Buying Anything

Leaf mould is naturally a slow process because it is driven by fungi rather than the heat-loving bacteria of a compost heap. You can hurry it along a little with a few tricks.

• Shred the leaves first by running over them with a lawnmower. Smaller pieces rot far faster than whole ones.
• Mix in grass clippings in thin layers. The nitrogen in the clippings feeds the fungi and speeds decomposition, but keep the layers thin or you will get a smelly, matted mess.
• Keep it damp. Bone dry leaves will sit there for years unchanged. If the bag feels dry, add a little water.
• Add a spadeful of old leaf mould to a new batch as a starter, just as you would with a yoghurt culture.

How to Use the Finished Product

After twelve to twenty-four months, depending on the leaves and the weather, you will have a material that is dark, soft and smells of the woodland floor. Sieve out any twiggy bits and return them to the next batch. Then put it to work.

Use it as a mulch around shrubs, perennials and fruit bushes, spread two or three inches thick in spring. Fork it into vegetable beds to improve structure. Mix it half and half with garden compost for a superb potting blend, or with sharp sand and loam to make your own seed compost. Leaf mould is also the secret to a decent fern, hosta and woodland border — it mimics the conditions these plants evolved in.

There is something quietly satisfying about turning a nuisance into a resource. The leaves you would otherwise bag up and send to the tip become, with nothing more than time and a bit of patience, the finest soil improver money cannot easily buy. Start a bag this autumn. Your soil will thank you for years to come.