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Every October the garden hands you a gift, and most of us rake it straight into a bag for the council to cart away. Those fallen leaves are the raw material for leaf mould, one of the finest soil conditioners you can make, and it costs nothing but a little space and a year of patience. Unlike a hot compost heap that needs a careful balance of greens and browns, leaf mould is made by fungi rather than bacteria. You are not so much composting as shepherding decay, slowly and quietly, in sacks behind a shed.
The result is a dark, crumbly, sweet-smelling material that holds moisture, improves soil structure and can be used on almost anything in the garden. It is also, quietly, one of the best slow-living jobs there is: a task you begin in autumn and forget about until the following year.
Not all leaves rot at the same speed, and knowing the difference saves disappointment. As a rough rule, thin, soft leaves break down quickly, while thick, waxy or leathery ones take far longer.
It is fine to mix them, though a sack of pure oak will simply sit longer than a sack of lime. Avoid sweeping up leaves that are thick with diseased material, and skip the leaves from beside busy roads or under treated timber, as they can carry pollutants you would rather not add to your beds. Conifer needles are worth keeping separately, as they make an acidic mould that suits blueberries, rhododendrons and camellias.
The simplest method is also the most effective. Use old compost sacks, rubble bags or the woven bags that logs and gravel arrive in. Punch a good dozen drainage holes in the base and sides with a garden fork, fill them loosely with leaves, give the sack a shake to settle them, then water it if the leaves are dry.
If you have more leaves than bags, a wire cage is a good alternative. Make a cylinder about a metre across from chicken wire or stiff mesh, held in place with a few stakes, and simply pile the leaves in. Tread them down lightly as you go, but do not compact them solidly, as the fungi need air. A third option is a wooden pallet bin with an open top, which is ideal if you want to turn the pile once or twice with a fork.
Whichever you choose, place it somewhere out of the way but accessible: behind the shed, under a hedge, along a north-facing wall. Keep the sacks off bare ground if you can, as worms will happily move in and help themselves, which is charming but does mean fewer leaves for you.
Moisture is the one thing that genuinely decides success or failure. Dry leaves will sit untouched for years, crackling and unchanged. Sodden leaves turn into a slimy, foul-smelling mess in a matter of weeks.
The aim is the dampness of a wrung-out flannel. If you are filling sacks in a dry autumn, add water as you go and check again after a fortnight. If the weather turns wet, make sure the drainage holes are clear and consider sitting the sacks on a couple of bricks. A sheet of old carpet or a piece of cardboard over the top of a wire cage helps hold in moisture without sealing it.
Do not add grass clippings, kitchen scraps or green prunings. That turns the process bacterial and you will end up with a stinking sludge rather than leaf mould. Leaves alone, nothing else, is the whole recipe. Label each sack with the month and year in permanent marker so you are not guessing later.
Check your sacks once a month or so, ideally on a mild, damp day when you are pottering anyway. Give them a squeeze. If they feel dry, add a little rainwater. If they feel heavy and sour, turn them out, mix in some drier leaves and refill.
By spring the leaves will have darkened and begun to stick together. By the following autumn most will have broken down into a coarse mulch, and by the second autumn you should have a fine, crumbly mould that runs through your fingers. Oak and conifer sacks may need a third year. That is not a failure; it is simply the pace at which those leaves live their lives.
There is a balance to strike, because a heap of leaves is also a small habitat. Hedgehogs, toads, frogs and countless beetles and invertebrates shelter in loose, damp leaf litter over winter. Rather than bagging every last leaf, leave a generous pile in a quiet corner under a shrub, and rake the rest into your sacks. You lose a little compost and gain a great deal of garden life.
Use your finished leaf mould as a mulch around perennials and fruit bushes, dig it into vegetable beds, or sieve it and mix it half and half with garden compost for a superb seed-sowing mix. A thin layer spread over a lawn in autumn will feed the grass gently without encouraging the soft, sappy growth that nitrogen-rich feeds produce.
Making leaf mould asks very little of you beyond restraint. You gather what the season gives, tuck it away, and let the fungi and the weather do the rest. A year from now you will tip out a sack of dark, earthy crumbs and realise you have turned a nuisance into the best compost in the garden.
The Quiet Rowan shares practical, down-to-earth guidance on seasonal cottage gardening, british wildlife and slow nature living for readers across the UK.
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