Why Leaf Mould Deserves a Place in Every Small Garden

Come late autumn, most of us are staring at a path, a lawn or a balcony corner covered in fallen leaves and thinking about the nearest green bin. That is a shame, because those soggy brown drifts are one of the best free resources a UK gardener can get their hands on. Leaf mould — simply rotted leaves — is a soil improver of the highest order. It holds water like a sponge, opens up heavy clay, brings lightness to sandy mixes and makes a superb base for seed and potting compost. Best of all, it costs nothing but time, and it takes up barely any space at all.

If you grow in containers, window boxes or a tiny courtyard, leaf mould is especially valuable. Bagged multipurpose compost dries out fast, slumps in the pot and loses its structure after a season. Leaf mould does the opposite. Mixed through your containers it keeps roots cool, holds moisture through a hot July and gently feeds the soil life that keeps everything ticking over.

Which Leaves to Collect — and Which to Leave Alone

Not all leaves rot at the same pace, so it pays to know roughly what you are gathering.

• Quick rotters (around a year): oak, beech, hornbeam, alder, lime and most hedgerow leaves.
• Slower customers (18 months to two years): sycamore, horse chestnut, sweet chestnut and walnut. Run them over with a mower, or scrunch them up in a sack, to speed things along.
• The awkward ones: holly, laurel and conifer needles are leathery and acidic, and can take three years or more. Use them sparingly, or rot them separately for acid-loving plants such as rhododendrons and blueberries.

Leave anything with obvious disease — rose blackspot, or horse chestnut leaves blotched by leaf miner — out of the bags, and skip leaves collected from the edge of a busy road if you can. A few stray twigs and conkers are fine.

The Bin Bag Method, Step by Step

• Pick a dry-ish day and gather the leaves with a rake, a stiff broom or gloved hands into a trug or old compost sack. An hour of raking usually fills several bags.
• Use heavy-duty bin bags, or better still old compost or builder's bags — they are tougher and far less likely to split. Black ones warm up nicely in the sun.
• Fill each bag about three-quarters full. Do not ram the leaves down hard; a bit of air is your friend.
• Water them if the leaves are tinder dry. You are aiming for damp, like a wrung-out sponge.
• Pierce eight to ten holes around the sides and base with a garden fork for drainage and airflow.
• Tie the top loosely, or simply fold it over.
• Stash the bags behind a shed, under a bench, beside a bin store or in a quiet corner of a balcony. Weigh them down so winter gales do not scatter them.
• Check every few months. Bone dry? Add a splash of water. Slimy and sour? Add more holes.

Squeezing Leaf Mould Production into Tiny Spaces

One of the joys of leaf mould is that it asks for almost no floor space worth speaking of. A stack of bags takes up less room than a water butt, and it can live somewhere you would never put a compost heap. On a balcony, tuck the bags behind a planter or beneath a shelf. In a small yard, a wire cage about a metre square, or an old dustbin with holes drilled through the sides, does the job neatly.

If you have no leaves of your own, ask around. A neighbour with a big garden, a friend with a lawn, or a local allotment holder will usually be delighted to see them go. Offering to sweep a communal path — with permission, of course — is another easy way to bag a free harvest.

How to Use Leaf Mould in Pots and Containers

After a year, the contents of your bags will be coarse, dark brown and partly broken down. This is perfect as a mulch. Spread a layer two to three centimetres deep over the surface of pots, window boxes and raised beds to lock in moisture and suppress weeds. Worms will pull it down and improve the soil beneath.

After two years, you have something genuinely special: crumbly, almost black, and smelling pleasantly of a woodland floor. Sieve it and it becomes a first-rate ingredient for homemade potting mixes. For general container growing, try roughly equal parts leaf mould and garden compost with a handful of grit or sharp sand for drainage. For seed sowing, sieve it finely and use it on its own or blended with a little sand. It is also wonderful for ferns, hostas and other woodland plants that hate drying out.

Troubleshooting and a Little Patience

Problems are rare, and almost all of them come down to air and moisture. A sour, stagnant smell means the bag is too wet and short of oxygen — prick more holes and give it a turn. Leaves that look exactly as they did last autumn are probably too dry; add water and shake the bag. Mice or squirrels may occasionally nest in a warm bag over winter. It is harmless, though if it bothers you, simply move the bag somewhere else.

Label each bag with the month and year, so you always know which batch is ready. Start a fresh lot every autumn and you will build a steady supply, with one year's mulch and two year's seed compost coming along behind it. There is something quietly satisfying about turning a nuisance into next season's growing medium — a little piece of the woodland floor, made for free in a bin bag on your balcony.