Mould glory: the rotten heart of gardening

It’s difficult to make leafmould sound sexy to someone new to gardening.

Even its fungal-sounding name can be enough to make them wrinkle their nose. Bang on for too long about its great usefulness as a soil conditioner that adds valuable organic matter, enhances soil structure and resilience, encourages a great diversity of beneficial soil micro-organisms, boosts plant health and increases productivity, and you risk being met with a barely suppressed yawn.

Talk for any length about how it’s one of nature’s great gifts to gardeners, a wonderfully sustainable, entirely free way to make their plants happy and healthy, and you’re likely to spot a glazed expression flitting across their face.

Nor– or at least not until you’ve learned to love its chocolate-like, fluffy crumbliness and the sweet earthy smell it emits – does leafmould look especially sexy.

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Pitted against any number of glossy gardening images, a pile of brown, rotted-down leaves is, let’s be honest, never going to win any horticultural beauty contests. Instead it’s only when you’ve observed its near-magical powers firsthand that you properly begin to appreciate just how wonderful it really is.

Making it couldn’t be easier.

All that’s needed is a generous pile of autumn leaves and some sort of simple container in which to hold them while they slowly rot down. Those same leaves should be damp, freshly-fallen and ideally from deciduous trees or shrubs – examples include beech, oak, alder, hornbeam, horse-chestnut, plane, ash, sycamore, elder and hawthorn.

As a rule, avoid using the waxy leaves of evergreen species such as laurel, ivy, griselinia and holm oak, which rot down terribly slowly and are instead much better chopped up and added to the nitrogen-rich compost heap. But if you particularly fancy the idea of making some leaf mould for the ericaceous/acid-loving plants in your life, then pine needles are a good choice.

As for the container you use, this can be anything from a couple of strong, black plastic bags (with a few holes punctured in them) placed in a shady, out-of-the-way spot outside to a purpose-built cage made from wooden posts and wire-netting (somewhere around 1m deep and wide is ideal).

Bear in mind that what looks like a large pile of leaves will rot down to between a third and a quarter of its original size. So if you don’t have enough freshly fallen autumn leaves in your own garden to make enough leaf mould (there’s no such thing as having too much leaf mould), then consider gathering them (but only with permission) elsewhere.

Suitable spots include friends and neighbours’ gardens, parks, local graveyards or even quiet streets, just so long as you’re sure that the leaves you collect are free of animal litter or nasty traffic pollutants. But never gather fallen leaves from woodlands, where they perform a vital role in supporting complex ecosystems.

Unlike a traditional garden compost heap that relies on heat and bacterial action for its contents to properly rot down, the process of turning leaves into leafmould is a slow, fungal one (hence the use of the word “mould” or “mold” as American gardeners call it) that requires cool temperatures, a little moisture and plenty of time.

By plenty of time, I mean at least one year, and as much as three if you want to make the finest, most crumbly leafmould, the sort suitable as an ingredient in homemade seed and potting mixes. You can speed the process up by shredding the leaves – running a lawnmower over them a couple of times will do the trick – as well as occasionally turning the pile to keep it oxygenated but even then, don’t expect fast results.

Bear in mind also that the leaves of some species (examples include sycamore, horse chestnut and plane) contain more lignin (organic polymers found in the cell walls of many plants) and will be slower to break down than those with less lignin such as beech, oak and birch.

While both homemade garden compost and leafmould make fine soil conditioners for your garden, they differ in other ways. The latter, for example, is lower in fast-acting plant nutrients but still hugely beneficial in terms of boosting precious humus levels.

Used as a surface mulch (up to 10cm deep), it will help to protect bare soil from the debilitating effects of climate change, boosting its ability to cope with winter flooding and summer droughts. It will also help with soil aeration while simultaneously suppressing weeds and protecting plants’ vulnerable root systems from frost damage.

Such are its wondrous qualities that it will make a heavy soil lighter and more friable while adding body and heft to a light, sandy one. Woodlanders in particular – examples include primulas, trilliums, Solomon’s seal, anemones, hellebores, spring-flowering bulbs such as snowdrops, scillas, eranthis, erythroniums, witch-hazel and Japanese maples – love it.

So do earthworms, which will slowly pull it deep down into their burrows, yet another way in which it helps to improve soil fertility, structure and drainage. Add a few handfuls of leafmould to your compost heap and you’ll also see the benefits in terms of worm activity.

In short, it’s quite magical. Some might even call it sexy.

This Week in the Garden:
Indoor plants' need for water dramatically decreases at this time of year as growth levels slow right down with the arrival of winter and lower light levels.

Overwatering is the most  common cause of their death so always check the compost before watering by sticking your finger into it (if it’s moist, hold off) as well as lifting the pot to check that it’s not sitting in a saucer of old water.

Most indoor plants also really dislike cold draughts so don’t place them near doorways or windows that are regularly opened. Likewise, avoid placing them very near radiators or heaters.

If you’re planning on using berried holly from your garden to decorate your home for Christmas , then it’s a good idea to cut it soon before hungry birds quickly strip the ripe berries from the plant. To keep it fresh, place the cut stems in a bucket of clean cold water in a dark, cool shed or outhouse until required.

Read this:
The updated and expanded edition of British landscape architect Kim Wilkie's classic Led by the Land, which has been widely acclaimed as "a major contribution to the literature on landscape, sustainability, regeneration and design". (£35), pimpernelpress.com

Dates for Your Diary:
At Knockrose Garden, The Scalp, Kiltiernan, Dublin 18 this weekend, Saturday November 23rd and Sunday November 24th (11am-4pm), 'Connected By Nature', a group exhibition by artists Bernard van Giessen, Erica Devine, Maeve Stafford, Fionnuala Broughan and Conleth Gent, all of whose work (photography, sculpture, botanical art and botanical casts) is directly inspired by nature, see knockrose.com

Tuesday November 26th (8pm), Foxrock Parish Pastoral Centre, Kill Lane, Dublin 18, 'Good in Bed (a look at those plants that have a particularly long interest in the garden and really earn their keep)', a talk by the Chelsea Gold medal-winning nursery owner, garden designer and horticulturist Annie Godfrey on behalf of Foxrock & District Garden Club.