Why Leaf Mould Deserves a Corner of Your Plot

Every autumn, a free resource lands on your lawn, your drive and the pavement outside your gate. Most of it ends up raked into the council bin. A smallholder should do something rather different: leaves are the raw material for leaf mould, one of the finest soil improvers you can make, and it costs nothing but a bit of space and a little patience.

Leaf mould is not compost. It rots down slowly, in the cool, by fungal action rather than the hot bacterial frenzy of a compost heap. The end result is dark, crumbly, sweet-smelling stuff that holds water like a sponge and opens up heavy clay like almost nothing else. Spread it on your beds and the worms will do the rest.

Which Leaves Are Worth Collecting

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

• Quick to break down (six to twelve months): sycamore, lime, ash, horse chestnut, field maple, poplar and most fruit tree leaves. Grab these first if you have a choice.
• Slow but excellent (up to two years): oak, beech, hornbeam, sweet chestnut and walnut. Worth the wait, because the resulting mould is superb — but keep them in a separate bin so they do not hold back the rest.
• Best avoided: conifer needles, holly and laurel. Acidic, waxy and slow — three years or more. A little pine needle is useful for ericaceous plants, but do not tip a whole sack into your main bin.
• Leave alone entirely: anything from a diseased tree, and leaves mixed with dog mess or litter.

If in doubt, mix it in. A blend of species generally rots more evenly than a single variety.

Gathering the Harvest

Timing matters more than technique. Wait until the leaves are dry and just fallen — a crisp morning after a dry night is perfect. Wet leaves mat down and turn slimy, which slows the whole process and smells unpleasant.

Rake them into a heap on the lawn and run the mower over them. Shredding a pile of leaves cuts the rotting time dramatically: what might take two years as whole leaves can be ready in one, sometimes less. If you have no mower, a strimmer in a dustbin works, and so does simply piling them up and letting the weather do the work.

Keep leaves out of your main compost heap. They slow it down and never heat up properly among kitchen scraps.

Building a Bin, Bag or Cage

Leaf mould needs three things: air, moisture and time. It does not need warmth, turning or any particular skill.

• Wire cage: four stakes and a length of chicken wire, roughly a metre square. Line the sides with cardboard in a dry spell to hold moisture in. The tidiest option, and it holds a lot.
• Bin bags: the classic cheat. Fill black bags with damp leaves, punch half a dozen holes in each for drainage and air, tie the tops and stack them behind the shed. They take up almost no room and suit a small garden perfectly.
• Cardboard box or old compost bag: fine for a modest quantity, though it will deteriorate within a year or two.

Site it out of the way. This is a slow crop and you will not want to look at it daily. Two bins side by side lets you start a fresh one each autumn while last year's gets on with rotting.

Leaving It Alone to Get On With It

Check the moisture occasionally. The pile should feel like a wrung-out sponge. If it is bone dry, water it. If it is sodden and smelling sour, fork it over to let air in — though in a well-made cage this is rarely necessary.

Turning speeds things up but is not essential. You will know it is ready when the leaves have lost all trace of their shape. The first year gives you a coarse, partially broken material that is ideal as a mulch. After two years it becomes fine, dark and crumbly — this is the good stuff, and a handful of it feels like velvet. Sieve it if you want a finer grade.

Putting Leaf Mould to Work

Leaf mould is a soil conditioner first and a fertiliser a distant second. It feeds the soil rather than the plant, which is exactly what most plots need.

• As a mulch: a 5cm layer around shrubs, fruit bushes and perennials suppresses weeds and keeps moisture in.
• On clay: fork in coarse, one-year-old leaf mould to open up the structure. On sandy soil it does the opposite job, holding water and nutrients that would otherwise drain away.
• For seed sowing: two-year-old, sieved leaf mould mixed half and half with garden soil and a little sharp sand makes an excellent homemade seed compost.
• In the kitchen garden: spread it over raised beds in autumn and let the weather work it in. Beans, brassicas and root crops all love it.
• Around acid lovers: a mulch of pine needle leaf mould suits blueberries, rhododendrons and camellias.

Start one bin this autumn, fill a few bags if you have not the space for a cage, and mark the calendar for a year from now. It is the nearest thing to free soil improvement a garden ever offers, and all it asks is a rake and a bit of patience.