Why Leaf Mould Deserves a Place in Your Garden

Every autumn the trees give you something for nothing, and most of us either ignore it or curse it. Those drifts of fallen leaves are the raw material for one of the finest soil conditioners you can lay your hands on, and making leaf mould costs nothing but a little patience. Unlike garden compost, which is broken down largely by bacteria, leaf mould is the work of fungi. The result is a dark, crumbly, faintly sweet-smelling material that is low in nutrients but unbeatable for improving soil structure, holding moisture and encouraging the soil life that keeps plants healthy. Spread it as a mulch and you will see the difference within a season: better water retention in sandy soil, easier cultivation in heavy clay.

Which Leaves Make the Best Leaf Mould

Not all leaves are equal. Thin, soft leaves break down quickly, while thick, waxy or leathery ones take far longer.

• Quick (roughly a year): oak, beech, hornbeam, lime, field maple, birch and most fruit tree leaves.
• Slow (up to two years): sycamore, horse chestnut, sweet chestnut, walnut and plane.
• Very slow: evergreen and conifer leaves — pine needles, holly and laurel. These are acidic and best kept in their own bin, then used around ericaceous plants such as blueberries, rhododendrons and camellias.

Leave out twigs, conkers, acorns and any leaves from diseased trees. If you garden beside a busy road, avoid the blackened leaves from the first metre or so of verge, which can carry exhaust residue.

Gathering Leaves: Timing, Tools and Shortcuts

Rake when the leaves are dry if you can, because wet leaves are heavy and mat together. Wait for a still, dry day after a frost and the job takes half the time. A tarpaulin makes the whole business easier: rake onto it, then drag it to your storage spot rather than filling and emptying barrow after barrow.

• A spring-tine rake for lawns, a plastic leaf rake for borders.
• A leaf blower on vacuum mode, which shreds as it collects.
• A rotary lawn mower, run over a thin scattering of leaves on the grass. This chops and collects in one pass, and chopped leaves decompose far faster than whole ones.

Shredding is the single biggest favour you can do yourself. A pile of whole leaves can sit for two years; the same leaves chopped will be ready in half the time.

Bags, Bins and Somewhere to Hide Them

The simplest method is also the cheapest. Fill black bin bags or old compost sacks with leaves, punch a few holes in the sides for air and drainage, add a splash of water if the leaves are dry, then tie the tops loosely and tuck the bags behind the shed or under a hedge. For larger quantities, build a wire bin by driving four stakes into the ground and wrapping chicken wire around them, or use a dedicated leaf mould cage made from timber and mesh.

Whichever you choose, keep the contents as damp as a wrung-out sponge. If the bag feels dry, water it; if it is sodden and smelly, add more holes and mix in some drier material. A handful of garden soil or old leaf mould stirred through the first bag helps introduce the fungi that do the work.

How Long Until It Is Ready?

Expect to wait. Shredded leaves in a well-ventilated bag are usually ready in eight to twelve months; whole leaves in a wire bin can take eighteen months to two years. Check by opening a bag in autumn: ready leaf mould is dark brown, crumbly and smells of woodland floor. A few stubborn leaf skeletons are fine for mulching, but for finer work sieve it through a garden riddle and return the coarse bits to the bin for another year. Speeding things up is simply a matter of chopping the leaves, keeping them moist and turning the heap once or twice.

Putting Your Leaf Mould to Work

Once it is ready, use it generously — you cannot really overdo it.

• Mulch: spread a 5cm (2in) layer around shrubs, perennials and fruit bushes, keeping it clear of stems and trunks.
• Soil conditioner: fork it into tired borders or simply lay it on the surface and let worms pull it down.
• Seed and potting mixes: sieved leaf mould mixed with garden soil and grit makes an excellent, free-draining mix for woodland plants, ferns, hellebores and bulbs.
• Lawn dressing: mix sieved leaf mould with sharp sand and brush it into the grass in autumn to level hollows and feed the soil.
• Compost bin booster: a layer of leaf mould between kitchen waste and grass clippings helps a cold heap behave itself.

Start a bag or a bin this autumn and you will have a free, steady supply of the best soil improver money cannot buy. It is the sort of quiet, thrifty gardening habit that pays you back every year.