The leaves have been falling for a while now. At first it was just a few spiralling down, puffed about on gentle breezes. A few weeks later there were lashing gales and autumn suddenly accelerated. Gusts sent flurries of leaves spinning through the air and scuttling down the street. Now, as I write a week or so before the end of October, some of the ‘early shedders’, such as the limes that line the lane, are almost naked. But other trees, especially the remnant oaks that survive on plot boundaries, remain resolutely green. It won’t be until early December that they’ll be completely bare.
Fallen leaves are one of nature’s gifts which any gardener or grower should welcome and put to good use. Unfortunately many people, including some gardeners who should know better, see fallen leaves as a seasonal nuisance, fit only for ramming into a recycling bin or, worse still, cremating on a smoky bonfire. How many tonnes of leaves are sent up in smoke every autumn, and how much carbon is emitted in their disposal, I hate to think. Surely there should be more emphasis on how to ‘harvest’ leaves and utilise them. For as all greener gardeners and growers will know, leaves have a variety of uses. What’s more, preparing them for these purposes is, on the whole, easier than stuffing them in a bin or burning them on a soggy and smouldering pyre.
One of the easiest options where there’s already a composting setup is to add leaves to the heap. However, it’s important to remember that composting is a heat generating, bacterially powered, action whereas leaves, which are primarily composed of cellulose and lignin, are naturally broken down by fungi in a slower and cooler process. Piling a huge wad of leaves onto a heap, especially if wet, will result in thick, mushy and poor quality compost. It’s therefore important to add leaves to compost heaps in layers. Make these thin if leaves are very wet, thicker if drier. Between each layer place other compostable material, ideally that which is fibrous, so that the mix isn’t too solid and airless. Added sparingly and mixed with other materials leaves will compost successfully, but for the patient grower there’s a better option, turning the gold of autumn leaves into leaf mould.
Leaf mould, should you not be familiar with the term, is the material obtained when leaves are naturally broken down in a heap composed of leaves alone. The ‘mould’, a not altogether appropriate label as good leaf mould is not ‘mouldy’, should be a dark brown, almost black, substance that’s crumbly and fine textured with a resemblance to peat. Indeed, it’s as a peat substitute that leaf mould can be used although it has a number of other garden applications depending on its age and quality.
There are two common methods of making leaf mould. The one I use, and the most practical where there are lots of leaves, is to build a large pile or ‘stack’. This should be surrounded by anything that’ll keep the leaves contained. I prefer to use old sheets of metal or recycled pallets for the sides, bolstered by posts. This makes a container less likely to bow or collapse as the stack sinks and consolidates. An alternative, and one I sometimes employ, is chicken wire strung between stout stakes. Regardless of how the sides are constructed the top of the stack is best left open to the elements. Rain will help keep the stack moist, dry leaves do not decompose readily. The other common means of making leaf mould, most suitable where there are smaller quantities of leaves, is to put them into bin liners or similar plastic bags. If doing this it’s essential the leaves are wet before the bags are packed. Also necessary is pricking a few holes in the full bags with a knife or fork to let in some air. Once filled the bags can be stored anywhere, outside in a shady corner will do.
It takes one or two years before leaves are decayed enough to be used horticulturally. One year old leaves aren’t usually fully broken down and are most suitable as a soil conditioner. Spread over or dug into the soil these will help lighten sticky clays and increase the water holding ability of light sands. Laid as a mulch, semi decayed leaves can also help retain moisture in summer and protect the soil from the elements in winter. It will also suppress most weeds if applied thickly. The only downside is that leaf mulches can provide a habitat for slugs so may be best avoided where there are vulnerable seedlings. It’s also worth remembering, whether dug in or spread as a mulch, leaves do not contain much in the way of nutrients. Generally leaf mould is not a substitute for compost or manure.
It takes one or two years before leaves are decayed enough to be used horticulturally. One year old leaves aren’t usually fully broken down and are most suitable as a soil conditioner. Spread over or dug into the soil these will help lighten sticky clays and increase the water holding ability of light sands. Laid as a mulch, semi decayed leaves can also help retain moisture in summer and protect the soil from the elements in winter. It will also suppress most weeds if applied thickly. The only downside is that leaf mulches can provide a habitat for slugs so may be best avoided where there are vulnerable seedlings. It’s also worth remembering, whether dug in or spread as a mulch, leaves do not contain much in the way of nutrients. Generally leaf mould is not a substitute for compost or manure.
Whereas one year old, half made, leaf mould is best used on the soil, two year old, which should be much more decayed, can be used for several additional purposes. One is as a peat substitute in compost mixes. I use a two year old leaf mould blended with garden compost and stacked turf (grass scooped up and turned upside down in a pile for at least a year) to grow tomatoes in large pots. It’s also possible to use leaf mould as an alternative to bought compost for sowing or raising seedlings. If planning to use in this way make sure weeds haven’t colonised the heap; if allowed to set seed weeds will readily sprout from any home-made compost! It may also be advisable to sieve leaf mould intended for tinier seeds to remove any chunkier lumps. It is sometimes said that not all leaves are suitable for making leaf mould. This is especially supposed to be the case for larger and thicker leaves such as horse chestnut or sycamore. Older gardening texts often insist that only oak and beech make high-class leaf mould. In my experience this is leaf ‘snobbery’. Almost all leaves from deciduous trees will break down into quality leaf mould within two years, if a stack is not allowed to dry out and the leaves are reasonably wet from the start. If there are a lot of bigger, thicker leaves an option is to shred them with a lawnmower before stacking.
More important than leaf size or thickness is where leaves are collected. Although I sometimes sweep up the leaves from the mown verges of our relatively low traffic lane, I’d hesitate to use any taken from a busier road because of the risk of pollution. A definite no-no is to take leaves from woodland. Done on any scale, this can disrupt the natural cycle of decay and the build-up of a leaf litter layer, as well as potentially affecting the flora, fauna and fungi that depend on fallen leaves. It could also be argued that all leaves should be left to decay naturally. Indeed, along with ‘No Mow May’, there is now a ‘Leave The Leaves’ lobby. In some parts of a garden leaving leaves uncollected may not matter, but on lawns and paths wet leaves can be damaging and dangerous. As with all things horticultural it’s a question of balance: Yes, leave some leaves but don’t overlook the value of leaf mould, nature’s annual gift to all gardeners.
We hope you’ve enjoyed reading Mr Fluttergrub’s findings. Do you have experience of making leaf mould? Do let us know. We’d love to have your point of view so we can add them to our social media when we share this article for the benefit of the WWOOF UK community and beyond. Email us: editor@wwoof.org.uk
Photos: Mr Fluttergrub
