Making Leaf Mould for Free Garden Compost

Why Bother Making Leaf Mould?

Every autumn, British gardens and allotments produce a free harvest that most people rake into a corner and forget about. Fallen leaves are the easiest soil improver you will ever make, and they cost nothing but a bit of patience. Leaf mould is not a fertiliser in the way that compost or manure is — it holds very few nutrients — but as a soil conditioner it is hard to beat. It improves structure, holds moisture in sandy soils, opens up heavy clay, and makes an outstanding mulch.

It is also the quiet secret behind good seed-sowing mixes. Once you have a bin of crumbly, dark leaf mould, you will wonder why you ever bought bags of the stuff. The best part? Nature does nearly all of the work. All you have to do is gather the leaves and wait.

Which Leaves Are Worth Collecting

Not every leaf is equal. The thinner the leaf, the quicker it breaks down. Good candidates include oak, beech, hornbeam, lime, and most fruit tree leaves. Oak and beech are especially prized because they rot into a lovely crumbly texture that seedlings adore.

Some leaves are better off in the compost heap or the council green bin:

• Conifer and evergreen needles — waxy and slow, they can take three years or more.
• Horse chestnut and sycamore — thick and leathery, they break down very slowly unless shredded.
• Leaves from diseased trees — rose blackspot is not carried on tree leaves, but if you spot something obviously sickly, keep it out.
• Leaves from busy roadsides — they can carry grime and salt, so leave those alone.

If you mix a few of the slower types into your bags, don't worry. Shredding solves most problems.

Bags, Bins and Wire Cages: Where to Put Them

You do not need a fancy setup. The classic method, used on allotments across the country, is the humble black bin bag. Fill it with damp leaves, punch a few drainage holes in the sides with a fork, tie the top loosely, and tuck it behind the shed. Make a handful of these each autumn and you will always have a supply coming through.

Wire cages are the other great option, especially if you have a lot of leaves. Roll a length of chicken wire into a cylinder, hold it with a few stakes, and pile the leaves in. A cage of about a cubic metre is a sensible size — any bigger and the middle dries out. Build two cages side by side so you can turn one into the other after a year, which speeds things along nicely.

Old compost bags, dustbins with the bottoms cut out, or a spare dalek bin all work too. Whichever you choose, keep the leaves damp but not sodden. If they dry out completely, the fungal action stops and you will be left with a bag of crispy leaves in two years' time.

The Waiting Game

Leaf mould is made by fungi rather than the bacteria that drive a hot compost heap, so it works slowly and coolly. Expect a bag of whole leaves to take one to two years to break down into a usable crumb. Shredded leaves can be ready in as little as nine to twelve months.

If you have the space, run the lawnmower over the leaves a couple of times before bagging them up. This chops them into small pieces, roughly doubles the speed of rotting, and lets you fit far more into each bag. A shredder works too if you have one, but the mower is quicker for most small plots.

Check your bags and cages every few months. If they look dry, add a little water. If they smell sour and slimy rather than earthy and mushroomy, they are too wet — open the bag, mix in some dry leaves, and start again.

How to Use Your Leaf Mould

Once the leaves have turned into a dark, crumbly material with a pleasant woodland smell, you have a genuinely versatile product. Fresh leaf mould — less than a year old — is still a bit coarse and is perfect as a surface mulch around shrubs, fruit bushes, and perennials. Spread it two to three inches deep in spring and it will suppress weeds and lock in moisture.

Well-rotted leaf mould, two years or older, is the real treasure. Use it in these ways:

• Seed sowing mix — sieve it and mix roughly half and half with garden compost or loam. It is low in nutrients, which is exactly what germinating seeds want.
• Potting on — add a couple of handfuls to your usual mix to improve water retention.
• Soil conditioning — dig it into vegetable beds in autumn and let the worms work it in over winter.
• Top dressing — sprinkle a thin layer around hungry crops like courgettes and brassicas.

Speeding Things Up and Common Snags

If you want leaf mould faster, mix in a handful of grass clippings or a little garden compost to add nitrogen. Turning the pile once or twice a year helps too. Keep the bags somewhere shaded and sheltered — tucked against a wall is ideal — because baking in full sun dries them out.

The most common mistake is forgetting about them entirely. A quick check in spring and autumn is all it takes. Even a small plot can make three or four bags a year, and once you are in the habit, you will never look at a drift of autumn leaves the same way again. Get them bagged, get them damp, and let nature get on with it.