Making Leaf Mould to Improve Your Soil

Why Leaf Mould Deserves a Place in Your Garden

Every autumn, the trees on your street and at the end of your garden quietly hand you a free soil conditioner. Leaf mould is not a fertiliser in the usual sense — it is low in nitrogen, phosphorus and potassium — but as a conditioner it is hard to beat. It opens up heavy clay, gives sandy soil some much-needed body, holds moisture through dry spells and feeds the earthworms and fungi that keep a border genuinely healthy.

It is also, quite literally, the cheapest growing aid you can make. All it costs is a few bin bags, a bit of patience and a dry afternoon with a rake. In a year's time you will have a crumbly, sweet-smelling material that is worth digging into every bed you own.

Which Leaves Make the Best Leaf Mould

Not every leaf rots at the same speed. Thin, soft leaves break down smartly, while thick and leathery ones ask for patience — sometimes two years or more.

• Quick to break down (roughly 12 months): ash, lime, maple, sycamore, willow, birch and horse chestnut.
• Slower (18 months to two years): oak, beech, hornbeam and sweet chestnut. These are still worth collecting; they simply need longer in the bag.
• Best avoided in quantity: evergreen leaves such as holly, laurel and conifer needles. Their waxy coating means they can sit around for years. Add them only in small amounts, or shred them first.

Skip leaves that are clearly diseased — rose leaves covered in black spot, for example — and think twice about gathering from a busy roadside kerb, where the leaf litter can carry grime and salt. Leaves from your own lawn, borders and quiet pavement are ideal.

Bags, Bins and Wire Rings: Choosing Your Container

There is no single right way to store leaves, and most gardeners end up using two or three methods at once.

• Bin bags. The classic. Fill black bags with damp leaves, punch a dozen drainage holes in the sides with a fork, tie the tops loosely and stack them somewhere out of full sun. This suits small gardens and rented plots, as the whole lot can be tucked behind a shed or against a north-facing wall.
• A wire cage. Make a cylinder roughly a metre across from stiff wire mesh or chicken wire, held in place with a few stakes. It holds far more than bags, lets in air and rain, and is easy to turn with a fork.
• A spare bin or builder's bag. An old dustbin with the bottom drilled for drainage works well in a courtyard, and a builder's bag is a neat solution if you have a corner going spare.

Whichever you choose, the principle is the same: keep the leaves damp, let air circulate, and leave the heap alone for the best part of a year.

Gathering and Storing: The Autumn Routine

Collect leaves when they are dry if you can. A dry, still afternoon after a frost-free night is perfect — the leaves lift off the lawn with a rake and weigh almost nothing. If you have a rotary mower, run it over the lawn with the leaves still in place; chopping them into smaller pieces can halve the time they take to rot, and the mix of grass clippings adds a little nitrogen to get things moving.

Before bagging or binning, give dry leaves a soak from a watering can, or leave the container open to the rain for a few weeks. The heap should be as damp as a wrung-out sponge. Then add a handful of garden soil or a little old leaf mould as a starter, label the container with the month and year, and forget about it.

One good habit is to keep two heaps going — one from last year that is nearly ready, and one from this autumn that is just beginning.

How Long, and How to Tell It's Ready

After twelve months, most leaf mould is coarse and partly broken down. This is perfect for mulching: spread a 5cm layer over bare soil in autumn and let the worms pull it in. Leave it another year and you get something finer and darker, more like woodland soil.

To test whether it is ready, take a handful and squeeze. Good leaf mould crumbles easily, feels soft and slightly damp, and smells sweet and earthy rather than sour. If it still looks like leaves, it simply needs more time — turn it with a fork, add a splash of water if it has dried out, and check again in spring.

Putting Leaf Mould to Work

Once you have a stash, you will find endless uses for it around the garden.

• Mulching borders: a generous layer around shrubs, perennials and fruit bushes suppresses weeds and locks in moisture.
• Improving soil: dig it into vegetable beds and allotment plots in autumn, or spread it on the surface and let the worms do the work.
• Potting mixes: sieve it and blend up to a quarter of the volume into your usual compost for containers and hanging baskets.
• Seed sowing: a traditional mix of one part sieved leaf mould, one part garden soil and one part sharp sand makes an excellent, free-draining medium for raising seedlings.
• Lawn care: a thin dressing raked over the grass in autumn helps level the surface and improve the turf's structure.

Start with a couple of bags this autumn, and by the following year you will wonder why you ever put leaves out for the council to take away.