Making Leaf Mould for Free Soil Conditioner

Why Leaf Mould Is Worth the Wait

Every autumn, most gardens produce a free crop that gets bagged up, carted to the tip or burned on a damp November afternoon. Fallen leaves are one of the best soil conditioners you can lay your hands on, and they cost nothing but a little patience. Leaf mould is not a fertiliser — it is low in nutrients — but as a soil improver it is hard to beat. It holds water, opens up heavy clay, gives body to sandy ground and creates the crumbly, dark texture that roots love.

The recipe is almost embarrassingly simple: gather leaves, keep them damp, leave them alone for a year or so. What you get back is a fine, earthy material that rivals anything you can buy in a bag. Here is how to make it properly.

Which Leaves Make the Best Leaf Mould

Not all leaves break down at the same speed, so a little sorting pays off.

• Quick to rot (6–12 months): oak, beech, hornbeam, field maple, lime, birch and most fruit tree leaves. Oak and beech are the classic choices and give a lovely fine product.
• Slow to rot (18 months–2 years): sycamore, horse chestnut, sweet chestnut, poplar and walnut. Perfectly usable, just give them longer and shred them if you can.
• Best avoided: conifer needles, holly, laurel and other thick, waxy evergreens. They take years and turn acidic. Keep them for a separate pile or leave them out altogether.

If you have a mix, don't fuss. Rake it all up, pick out the twigs and conifer needles, and get on with it. Running a lawnmower over a drift of leaves a couple of times shreds them nicely and can cut the rotting time by several months.

Two Ways to Make It: Bin Bags and Wire Cages

The bin bag method is ideal for small gardens, courtyards and anyone short on space. Use strong black bags — the dark colour helps hold warmth. Fill each bag loosely, add a splash of water if the leaves are dry, then tie the top. Puncture the sides a few times with a fork or scissors so air can get in and excess water can drain. Tuck the bags behind a shed, under a hedge or beside the wheelie bins. Check them every few months; if the contents feel bone dry, add a little water.

The wire cage method suits larger gardens and gives you bigger volumes. Make a cage roughly a metre square and a metre high from chicken wire wrapped around four wooden stakes, or use an old pallet collar. Fill it as leaves arrive through autumn, treading them down gently every so often. A lid of old carpet, cardboard or a tarpaulin keeps them from blowing about and stops them drying out, while still letting rain in at the sides. Two or three cages let you have a batch rotting while this year's leaves go into the next one.

Whatever you choose, keep the leaves separate from your normal compost heap. Mixed in with kitchen and garden waste they slow the whole process down; on their own they do their own quiet thing.

Keep It Damp and Let the Fungi Do the Work

Leaf mould is made by fungi rather than the bacteria that drive a hot compost heap, and fungi need consistent moisture. Aim for the dampness of a wrung-out sponge. If you squeeze a handful and no water shows, it is too dry — water it and turn it lightly. If it is slopping wet and smells sour, fork it over and leave the lid off for a few days.

A handful of grass clippings or a light sprinkle of a nitrogen-rich feed between layers can speed things along, but it is not essential. Mostly, this is a job of doing nothing at all. After twelve months you will have a coarse, dark material that is perfect as a mulch. Leave it another year and it becomes a fine, crumbly conditioner you can use in potting mixes. Sieve out anything still recognisable and return it to the next batch.

How to Use Your Leaf Mould

• Mulch: Spread a 5–8cm layer over borders in spring or autumn to suppress weeds, conserve moisture and feed the soil life beneath.
• Soil conditioning: Fork the finer stuff into vegetable beds and around shrubs to improve structure. It is especially good on clay and sandy soils alike.
• Potting mixes: Mix one part sieved leaf mould with one part garden compost and one part loam or grit for a lovely free-draining mix for pots and containers.
• Lawn dressing: In autumn, sprinkle a thin layer over the grass and brush it in. It improves the soil under the turf without encouraging soft, sappy growth.
• Seed sowing: Well-rotted, sieved leaf mould makes a fine, low-nutrient medium for sowing seeds and potting on seedlings.

Start a batch this autumn, even if it is just three bin bags behind the shed. This time next year you will have a free supply of soil conditioner, and the year after that, something genuinely special. It is the easiest bargain in gardening.