Making Leaf Mould for Free Garden Compost

Why Bother With Leaf Mould?

Every October and November, British gardens are buried under a fortune in free organic matter. Those drifts of fallen leaves are not rubbish to be bagged up by the council and carted away — they are the raw material for one of the finest soil improvers you can get hold of, and it costs you nothing but patience.

Leaf mould is what you get when leaves are broken down by fungi rather than the bacteria that drive a hot compost heap. The result is a dark, crumbly, sweet-smelling material that holds water beautifully, improves soil structure, and can be used as a mulch, a soil conditioner, or sieved and mixed into seed and potting composts. It is low in nutrients compared with garden compost, which makes it ideal for young plants and seed sowing where you do not want to push soft, sappy growth.

The best part is how little effort it takes. Unlike a compost heap, leaf mould needs no turning, no balancing of greens and browns, and no attention at all over winter.

Which Leaves to Use — and Which to Leave Alone

Most deciduous leaves are excellent. Oak, beech, hornbeam, field maple and hazel all break down into particularly good leaf mould. Sycamore, lime and horse chestnut are fine too, though they rot a little more slowly because of their thicker texture.

• Best: oak, beech, hornbeam, field maple, hazel, birch
• Good but slower: sycamore, London plane, horse chestnut, sweet chestnut, walnut
• Avoid or use sparingly: laurel, rhododendron, cherry laurel and holm oak — these are thick, leathery and waxy, and can take three years or more
• Conifers: pine and other evergreen needles are acidic and slow, so keep them separate and expect a longer wait

Avoid sweeping up leaves from roadsides where there is heavy traffic, and skip any that are covered in dog mess or came from beneath a plant you know has been sprayed. Otherwise, if it falls in your garden, it is fair game.

The Black Bag Method

This is the simplest approach and the one I recommend to anyone short of space or time.

• Rake or vacuum the leaves into a pile. If you have a rotary mower, run it over the pile a few times — shredding the leaves roughly halves the decomposition time.
• Fill strong black bin bags or old compost sacks, roughly three-quarters full. Do not cram them so tightly that they become solid blocks.
• Add a splash of water if the leaves are bone dry. You want them damp, like a wrung-out sponge, not soaking.
• Punch or stab half a dozen drainage holes in the bottom and sides of each bag. This lets air in and excess water out.
• Tie the tops loosely, label the bag with the month and year, and stack them somewhere out of the way — behind the shed, beside the bin store, against a north-facing wall.

Then walk away. Check them once or twice over the year; if they look dry, add a little water. That is the whole job.

Wire Bins, Wooden Moulds and Other Options

If you have more leaves than bags, a simple wire cage is a good upgrade. Make a cylinder roughly a metre across from galvanised wire mesh or chicken wire, held in place with a few stakes. Fill it with leaves and leave it open to the rain. The material in the middle will rot faster than the edges, so give the heap a fork-over once in spring if you remember.

An old dustbin with the bottom cut out works well too, as does a wooden slatted bin. If you would rather not see the heap at all, a plastic sack tucked behind the greenhouse is perfectly respectable.

One more trick: if your lawn has a light scattering of leaves and you cannot be bothered to collect them, set the mower to its highest cut and run over them. The chopped fragments will disappear into the grass within a fortnight and feed your lawn for free.

How Long, and How to Tell It Is Ready

Leaf mould is made on nature's timetable, not yours. Expect roughly:

• One year: a coarse, partially broken mulch — perfect for spreading around shrubs and trees
• Two years: a crumbly, fibrous material you can dig into borders as a soil conditioner
• Three years or more: a fine, dark, peat-like substance that can be sieved and used in potting mixes

The sign it is ready is simple: you cannot tell what kind of leaf it was. If you can still recognise a sycamore, give it another six months.

Using Your Leaf Mould

Spread it as a mulch 5–8cm deep around shrubs, perennials and fruit bushes to suppress weeds and hold in moisture. Fork it into tired, heavy clay or thin, sandy soil to improve structure. Mix it roughly half and half with garden compost for a superb general-purpose planting mix.

For seed sowing, sieve it finely and combine two parts leaf mould with one part sharp sand and one part good loam. It is also the traditional ingredient in homemade potting composts, and unlike peat, it is a genuinely renewable resource you made yourself from what your trees dropped.

So next autumn, before you reach for the rake and the council green bin, fill a few bags instead. A year from now you will have a free supply of the best soil improver money cannot buy.