Making Leaf Mould for Your Garden

The Best Soil Conditioner You Can Get for Free

Every autumn, British gardens produce a crop nobody planted. Oak, beech, sycamore and lime drop it across lawns, paths and borders, and most of us spend a weekend raking it into bags and carting it to the tip. It is worth stopping and looking at that haul again, because fallen leaves are one of the finest soil conditioners available to any gardener, and they arrive free of charge, every single year.

Leaf mould is not compost. It is what you get when leaves are left to rot slowly with the help of fungi rather than the hot, bacterial rush of a compost heap. The result is dark, crumbly, sweet-smelling material that holds water like a sponge, opens up heavy clay, gives body to sandy soil and teems with the soil life that feeds healthy plants. It contains very little in the way of nutrients, so it is not a fertiliser. What it does is improve the ground itself, and no bagged product does that better.

Which Leaves Earn Their Keep

Not all leaves break down at the same speed, and knowing which is which saves a good deal of disappointment.

• Quick, roughly a year: sycamore, horse chestnut, lime, willow, poplar and ash. These soften and rot readily.
• Slower, up to two years: oak, beech, hornbeam and sweet chestnut. Oak and beech make arguably the finest leaf mould of all, but you must be patient with them.
• Very slow, three years or more: conifer needles, holly, laurel and other thick, leathery evergreens. Pine needles give a slightly more acidic product, which suits rhododendrons, camellias and blueberries.

Speed things up by shredding. A pass with the lawnmower over a spread-out heap, or a few minutes with a shredder, halves the volume and roughs up the leaf surfaces so the fungi can get to work. Mixing quick and slow leaves together in the same bin also helps, as the fast rotters get the process moving.

Two Simple Ways to Store Them

Whatever container you choose, the principle is identical: damp leaves, in the dark, with air moving through them.

• A wire bin. Knock four sturdy stakes into the ground and wrap chicken wire around them to make a cage roughly a metre square. Site it somewhere shaded and out of the way, behind a shed or under a hedge. Fill it with leaves, tread them down to exclude air pockets, and leave it. A bin this size holds an astonishing quantity of leaves once they are pressed down.
• Bin liners or old compost sacks. Cheaper, tidier and ideal for small gardens. Half-fill each bag with damp leaves, punch a handful of drainage holes in the sides and bottom, tie the top loosely rather than sealing it, and stack the bags in a corner. A row of sacks behind the garage is a perfectly respectable leaf mould factory.

Do resist the temptation to send leaves to the council green waste collection. You are giving away the raw material for the best soil improver your garden will ever see.

Damp, Dark and Patient

Leaf mould is made by fungi, and fungi need moisture. Keep the contents of your bin or bags as damp as a wrung-out sponge. If the leaves were dry when you gathered them, water each layer as you fill the bin, or give the bags a soak before tying them. Through a dry summer, check the bin and water it if the leaves are crisp.

Turning is helpful but not essential. Twice a year is ample: fork the pile from one side to the other in spring and again in autumn, which mixes the outer, drier leaves into the damp middle and lets a little air in. You will see the change as you go. After twelve months the leaves will have broken into a coarse, brittle mulch. After two years you will have a soft, crumbly, dark brown material that smells pleasantly of woodland floor. Leave it a third year, sieve it, and you have something close to fine potting compost.

Putting It to Work

• One-year mould: use as a coarse mulch around shrubs, roses, fruit bushes and perennials, spread 5–8cm deep. It suppresses weeds and holds moisture through summer.
• Two-year mould: fork it into vegetable beds and borders as a soil conditioner, or spread it thinly over a lawn in autumn as a top dressing and let the worms pull it down.
• Three-year, sieved mould: mix with garden compost and a little grit for seed sowing and potting on. It is low in nutrients, which is exactly what young roots want.

Leaves, Wildlife and the Water Course

A leaf pile is one of the simplest pieces of wildlife gardening you can do. Left in a quiet corner, it shelters hedgehogs looking for somewhere to hibernate, frogs and toads, beetles, centipedes and the pupae of moths. Do not sweep every last leaf from under hedges and shrubs; that thin litter layer is where blackbirds, wrens and thrushes hunt for grubs through the winter, and where many insects spend the coldest months.

Do, however, keep leaves out of drains, gullies and gutters. Sweep paths and driveways before the rain arrives, because leaves washed into the drainage system can block it, and in quantity they add nutrients to streams and rivers, encouraging the algae that starve water of oxygen. Rake them off the grass, gather them from the paving, and tip the lot into your bin or bags. In a year or two you will have a barrowload of dark, crumbly gold — and a garden that holds its moisture, feeds its soil and looks after its wildlife, all from something you were going to throw away.