Why Leaf Mould Is Worth the Wait

Every autumn Britain drops tonnes of free soil improver on our lawns, paths and pavements, and most of it ends up at the tip or in a bonfire. Leaf mould is what you get when fallen leaves are broken down by fungi rather than by the bacteria that drive a hot compost heap. The result is a dark, crumbly, sweet-smelling material that is one of the finest soil conditioners you can lay your hands on.

It is not a fertiliser. Leaf mould contains very little nitrogen, potash or phosphate, so don't expect it to feed hungry crops on its own. What it does brilliantly is improve soil structure, hold moisture, open up heavy clay and give sandy soils something to cling to. It is also alive with fungal life, which is exactly what shrubs, perennials and woodland plants enjoy. Best of all, the raw material arrives on your doorstep every year, free of charge.

Which Leaves Are Worth Collecting

Not all leaves rot at the same speed, and a little sorting now saves a lot of waiting later.

• Quick to break down (roughly a year): sycamore, lime, ash, birch, cherry, horse chestnut and most fruit tree leaves.
• Slower (up to two years): oak, beech, hornbeam and sweet chestnut. Their tough, leathery leaves are high in tannins and lignin, so be patient with them.
• Very slow: conifer needles, holly, laurel and other evergreens. They will rot eventually, but can take three years or more, so keep them in a separate bag or bin.

Skip leaves from busy roadsides, where they can carry oil and exhaust residue, and shake out any litter before bagging. If you can only collect one type, sycamore and lime are the gardener's favourites: soft, plentiful and quick to transform.

How to Collect and Store Them

Damp leaves are easier to handle than dry ones, so a day or two after rain is ideal. Rake them onto a tarpaulin or old sheet, vacuum them up if your blower has that setting, or run the lawnmower over them on the lawn. The mower shreds them as it goes, and that alone can halve the breakdown time.

Then choose your container:

• Bin bags: the cheapest option. Punch a few holes in the base for drainage, fill them, tie loosely and stack them behind the shed.
• Wire cage: four stakes and a length of chicken wire, about a metre square. Fill it as leaves arrive and tread them down.
• Old compost bin or dalek: works well, especially with a lid on top to stop the contents blowing about.

Whatever you use, water the leaves in as you fill, and check the following spring that the pile is still damp. Dry leaves will sit there doing nothing for years.

Speeding Things Along

Leaf mould is not a quick process, but you can nudge it. Shredding is the single biggest help. Mixing in a little nitrogen-rich material, such as a thin scattering of grass clippings, a handful of garden compost or a sprinkle of poultry manure pellets, gives the fungi something to work with. Keep the pile moist but not sodden, and turn it once or twice a year if you have the energy.

If you have room, two bins work better than one: this year's collection goes into the empty one while last year's quietly finishes off.

Knowing When It's Ready

Fine, soft leaves such as lime and sycamore can be ready in nine to twelve months. Oak and beech usually need eighteen months to two years, and conifer needles longer still. A pile started this autumn will be worth sieving the autumn after next.

You will know it is ready by feel and smell rather than by the calendar. Good leaf mould is dark brown, crumbly and earthy, with no recognisable leaves left. Push a handful through a garden sieve and use the fine stuff for potting and seed sowing; tip the coarse remains back into the bin for another year. Label your bags with the date you filled them, and future you will be grateful.

Putting Leaf Mould to Work

• Mulch: spread a 5-8cm layer around shrubs, perennials, fruit bushes and hedges to suppress weeds and lock in moisture.
• Soil improver: dig it into vegetable beds, or spread it on the surface and let the worms do the work. Clay soils become more workable and sandy soils hold water for longer.
• Seed sowing: sieve it and mix with equal parts garden compost and sharp sand or grit for a lovely peat-free seed mix.
• Potting: blend sieved leaf mould with composted bark and a little loam for a homemade potting compost.
• Lawns: mix with sand and brush thinly into the grass as an autumn top dressing.

Start a bag or a wire bin this autumn, water it, label it and forget about it. Two years from now you will have a barrowload of the best soil improver on the plot, and you won't have paid a penny for it.