It’s a good month for mould. The days are shortening, the busy season of gardening is behind us, but the fungal underlayer is just starting to really get to work.
As the leaves are beginning to fall, I keep a greedy eye on them, ready to make the most of their bounty. Now is the time to make leaf mould and I am excited.
Crunching on the drying leaves and humming ‘California Dreamin’’ (the leaf mould-maker’s earworm), I think about all the work the natural world is about to do and the many benefits my garden will soon be gifted.
Leaf mould is perhaps the greatest gift the lazy gardener is given – such little work for such high reward. I never have quite got over the magic of the stuff – weed suppressor, perfect seedling compost, moisture-holder, soil aerator – and it’s all for free.
To understand the wonder of leaf mould, it makes sense to first understand the wonder of trees – and what wondrous things they are!
After a busy spring and summer of photosynthesis and growth, trees begin to shift into their dormant stage. The nutrients gathered are drawn back into the branches and trunk, and the trees bid us adieu with their multi-copper-coloured finale before dropping their leaves in preparation for the darker months. There are a few reasons for this – it expends less energy, it conserves moisture within the trunk, and the leafless branches allow wind to blow through more easily, putting less strain on the tree during the winter storms and gales. These fallen leaves, though, are not waste material (is there such a thing as waste material in nature?). They fall around the base of the tree forming a layer alive with micro and macro organisms. And thus leaf mould begins to form.
The process that follows is at once simple and endlessly complex. In essence though, the autumn leaves slowly decompose with the help of fungi and any number of critters, turning from light papery leaves into a dark crumbly substance. The nutrient level is low, the moisture retention is high and the texture is light, making it the perfect mulch (those trees know how to look after themselves).
It is not just the trees that can make good use of the stuff though. The light-weight consistency of leaf mould makes it the ideal soil amendment. Good growing conditions require aerated soil, so adding some leaf mould is just the ticket to achieving optimum soil structure in your beds or containers. The low nutrient content is also great for using as seed compost. It can be used as a mulch around the base of trees and shrubs too, to help conserve moisture, moderate soil temperature and protect roots from extreme summer and winter temperatures.
There are several ways to make leaf mould. Those fungi that do all the hard work breaking down the leaf structure do best in damp, airy conditions. Traditionally, this meant making a leaf mould cage out of chicken wire and allowing the autumn rains to do the work, but if you don’t have space for a cage, recycle old compost bags. These are ideal because they’re tough and won’t disintegrate, unlike bin liners, say. Punch extra holes into the bags with a fork to improve air flow, fill them up with your leaves, pour a little water in there to keep it all nice and soggy and then tuck them into an out-of-sight corner and let the fungi work their magic. It will be ready to use in about a year’s time, but you can leave it there for longer and take out what you need for years to come.
‘Go lightly when foraging leaves’
You can give the leaves a head start by breaking them down a little first – just bash them about with a spade, or get your blood pumping with some energetic leaf-stomping.
Or take the lazy route, which is increasingly my preferred one. Gather up wet, semi-rotten leaves over the next few months (staying away from leaves on roads – they are often contaminated), spread them over the surface of bare soil and leave the worms to it. They will bury a good percentage to line their burrows.
It’s best to let the leaves decompose as close to a tree as possible, because there the fungi doing the hard work for you will be especially populous. If you can’t do that though, not to worry, the leaves in your pile will already host plenty of spores from the fungi present – being close to a tree will just speed up the decomposition.
When it comes to what leaves to go for, us Hackneyites are spoiled for choice. There are over eight million trees in London – an urban forest that covers around 21 percent of the city. And thanks to a pioneering program of tree-planting over the last 20 years, Hackney has a more diverse population of trees than any other borough in London. Paul Wood, the aptly named author of London’s Street Trees, estimates that the area boasts at least 350 species.
If you’re looking for a pleasant way to while away some time, Hackney Council’s website has a wonderful tree map that lists the 45,000 street trees in our borough, detailing their location, species, common name, and age.
The holy grail of leaf mould is made from oak or hornbeam, matured for two years. If you have the patience to do this, you will make the best seedling compost money can’t buy. Pine needles are worth gathering and placing in a separate pile as they produce acidic leaf mould, which is ideal for mulching ericaceous plants, such as rhododendrons, azaleas, camellias, and blueberries.
The general rule of thumb is that the stiffer the leaves, the longer they will take to break down, so go for species such as ash, beech, birch, cherry, elm, hornbeam, lime, oak, poplar and willow for speedier results.
As ever, go lightly when foraging these leaves. They are as excellent for the forest floor and your lawn as they are for our pots and beds, so be sure to gather small amounts from different spots. Other than the leaves you take for making leaf mould, leave the rest!
There is overwhelming evidence for how beneficial leaves are for the natural environment, and yet, every autumn the din of leafblowers begins, spewing out clouds of carbon dioxide. Leaves are cleared from the bases of trees and under hedges (the exact places they are needed most), and bagged up to be shipped to landfill. Without enough oxygen to decompose, the bags of organic matter release the greenhouse gas methane.
The only garden area that really needs to be cleared are the paths, which can be done very effectively with a rake. And if you’re wondering what to do with all that extra time you have saved? Well, why not join me in writing to Hackney Council to ask that they stop clearing the autumn leaves too.
Steph Goward is an ecological gardener and food grower. She is the postcode gardener for E5, a horticultural therapist at St Mary’s Secret Garden, and works with a number of gardening groups across Hackney. You can follow her at @steph_orla_gardens.