Falling Assets: How to Turn Your Free and Renewable Autumn Leaves Into Rich, Life-giving Leaf Mould to Improve Soil and to Make Your Own Peat-free Potting Compost

Canny gardeners don’t leave any leaves lying – this beautiful and noisy autumn windfall matures into gardening gold that’s free for the raking, and is infinitely renewable year after year after year…

By John Walker. Published on the Hartley Botanic website, 7th October 2014
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Of all the free gifts nature gives to gardeners, autumn leaves are both seriously useful and infinitely renewable.

There’s one turning of the seasons which arrives here with a right old clatter. After a cold jolt in August, most gardeners have been teased throughout September with only vague hints of impending autumn. In my garden, warm, balmy days and the on-and-on-and-on growth of sweet peas, mangetout peas and runner beans – not to mention defiant, please-let-me-set-just-one-more-truss tomatoes, plus runaway weeds – have taken my eye off the clues all around. A bronze tint amongst the larches, rust flushing into the oaks, and butter-infused willows have all crept up on me thanks to subconscious blind-eyeing. Even the pumpkins, orange skins deepening by the day, somehow slipped from the scene. So far my garden has only flirted with frost, but the clock is now ticking. Autumn begins officially here when I wake to a deep blue sky, brilliant, squint-making sunshine, and a clattering chorus of falling leaves. Any day now.

Of all nature’s free and infinitely renewable gifts to gardeners, fallen leaves are right at the top of my list. Sunshine and rain come close behind, but they lack the grab-a-handful quality of leaves and – in their own good time – the product of their unhurried, magical decay: leaf mould. Being effectively manure-less here (and wanting to eliminate animal-derived inputs anyway), I’ve had to rely more on other, gentler ways of mustering my soil’s fecundity. Adding compost, mulching with seaweed and growing green manures have all played their part, but the most conspicuous, most multipurpose, and most copious ally to my garden-making is leaf mould. Enjoy a twinge of envy when I tell you that I collect builders’ bags brimming with leaves from along the lane here, but even modest leaf-gathering yields something useful – even if it’s just enough leaf mould to mulch your indoor plants.

“Of all nature’s free and infinitely renewable gifts to gardeners, fallen leaves are right at the top of my list.”

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My big leaf mould ‘cages’ overflow at collection time, but soon sink (as in the cage on the left) as countless leaf moulders get to work.

I gather up my leaves (ideally when wet) using a spring-tine rake and two pieces of 60cm long floorboard (to give me longer fingers), and pour them into 2m diameter, 90cm deep circular wire mesh ‘cages’, of which I have three (1m wide is the minimum to go for). Each year I aim to empty the cage containing the maturest, crumbliest leaf mould, before refilling it with fresh leaves. With a three-cage system I can, depending on what I need it for, dive into leaves in any of their stages of slow, glorious decay. This spring, the dark ‘crumble mix’ I sieved for my home-made, peat-free potting compost was all that remained from 2010’s autumn haul. This crumble is mixed half-and-half with worm-turned, sieved compost from one of my ‘cool’ bins, which gobble up kitchen and household waste. Leaf mould gives my DIY mix its body and holds onto water, while the rich worm-workings give it added oomph. I use it for sowing and potting up, and bar a few weed seedlings, it works a treat. But digging out this sweet-smelling crumble marks the end of a longer journey, with spin-offs for wild life of all sorts along the way.

The first thing that happens to my brimful cages is that they heat up, even steaming a little on sub-zero mornings (they don’t match the finger-scalding temperatures in a big, well-mixed ‘hot’ compost heap). This brings blackbirds and thrushes, flicking through the top layers, and wrens skittering over the cages, picking off insects. Next up is the invasion of the fungi. Although most leaf-moulderers go about their quiet business unseen, I often get a sudden show of toadstools pushing up from the warm, settling mass. As things cool off toward winter, in come small, red and lively worms (more flicking, sometimes by an odd jay or raven). These relocate from the surrounding soil, along with gazillions more of nature’s unseen decomposers. Toads, frogs, newts and slow-worms move into the ground floor to hole up for winter (look out for them when you’re taking leaf mould out).

“I often get a sudden show of toadstools pushing up from the warm, settling mass.”

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Sieving leaf mould gives dormant muscles a workout. It also gives me a fine ‘crumble mix’ for use in my own peat-free potting mix, and coarser sievings for mulching and to use as soil improver.

By spring the early heat is long gone, and below the crisp top layer, mouldering is full-on, pale strands of mycelia weaving amongst their feast. If I need coarse, chunky mulch, these just-rotting leaves are just the job. I’ll take them straight from the cage, or pass them through a 25mm sieve to remove twigs. If I need soil improver, my 13mm sieve gives me something finer, which works easily into my soil beds (try a bucketful per square metre, forked into the top 10cm). As spring unfolds, the level in a cage soon sinks; you can expect, eventually, to take out around a third, at best, of the volume that originally went in. I try hard not to disturb a cage until it’s at least a year old, which is easier when there are three on the go (never settle for less than two). As the birds seek richer summer pickings and worms head off back into the soil, voles and mice tunnel through the settling heap, and fledgling oaks and hazels sprout. After a full year, most leaves will have fragmented and lost their identity; the deeper in the mass you dig, the less recognisable they become. Only the toughest bits are left behind, and these make up the final, spongy crumble.

If you manage to let your leaves moulder undisturbed for a whole year, by the following spring you can harvest mulch, soil improver and potting mix material (my 6mm sieve gives a fine grade that’s ideal). Time does the hard graft; the longer you lay off your leaves, the finer the mould becomes, and nothing ever needs turning. Any tough, sieved-out bits are tossed back into the cage (or the next-door one) to keep on rotting.

“If you find great swirling ‘leafdrifts’ forming in your local park, see if it’s all right to go along and bag some.”

You don’t need big cages to make leaf mould. Turning an empty compost bag inside out, stuffing it with leaves (pack them in firm, but not tight), tying it off, and jabbing some holes all over it, works fine. Filling a reused builders’ bag (or three) with leaves, then lashing its handles together, is a piece of cake. Leaves simply piled up in an unused corner will eventually become crumble. Your only limit is the amount of leaves you can get your mitts on, so it pays to source laterally. Once you’ve scooped up everything from your own patch, ask the neighbours if you can have theirs (as a sweetener, offer to go and collect them). If you see bin bags filled with leaves on the street, ask if you can have them. If you find great swirling ‘leafdrifts’ forming in your local park, see if it’s all right to go along and bag some – or perhaps think about organising a community ‘love those leaves’ day, by collaborating with your local authority (so that health and safety requirements are met).

Leaves will soon be everywhere, so grab them while you can. I can’t wait for the clattering to begin.

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