Let Fallen Leaves Lie

Autumn leaves fall, collecting in piles along roadsides, and creating colourful carpets across open areas. They can be slippery, encourage blockages, and deprive lawn spaces of the sunlight the grass needs to survive. But are there times when we should let fallen leaves lie?

The garden here is home to many – including nesting birds, a hedgehog, numerous insects and mini bugs, and a selection of aquatic life. Regular visitors include foxes, and other birds – from stock doves to magpies, robins to sparrows. For the last couple of years, I have extended my ‘no mow May‘ commitment to ‘one mow a year’. Leaving the grass to grow provides food and shelter for insects and other wildlife, and the lawn doesn’t grow out of control. As winter approaches, I turn my attention to what to do with the leaves lying across the lawn.

Nature’s Cycle

Fallen leaves are part of nature’s cycle. Without human intervention, they would remain on the ground, to continue their contribution to the environment. Rewind to spring, when the leaves of deciduous trees begin to grow from branches. A layer between leaf and tree, known as the abscission layer, is formed during the growth. Through this layer, the leaf passes energy to the tree, which is stored for later in the year. As autumn approaches, and temperatures drop, hormone production in the leaf also falls, leading to a weakening of the abscission layer bond. Eventually, the weakened bond means the leaf falls from the tree. The process of shedding leaves enables the tree to save both energy and moisture during winter months. It also means strong winds put less strain on the tree, as they blow straight through the empty branches rather than tangling within foliage.

Leafmould

Leaves which are left to lie where they fall undergo a fungal process which rots them down into leafmould. This provides a source of rich nutrients for soil, and can help to deter plants which would otherwise compete with trees for the nutrients. Deciduous leaves shed in gardens can be collected when damp, stored (separately from compost which is broken down through a bacterial rather than fungal process), and used as mulch.

After a year or two, young leafmould can be used to keep lawns healthy by keeping soil moist, and suppressing plants which might overrun the area. It can also be dug into heavy soil to encourage better drainage, which enables grass roots to thrive. More mature leafmould (over two years old) provides a suitable balance of nutrients for seeds to germinate, or to keep established pot plants healthy.

When To Let Fallen Leaves Lie

Leaves which have fallen directly onto grass can be left where they fall. To avoid the lawn being overwhelmed, using a mower without a hood will distribute the leaf cuttings around the area. Smaller cuttings begin to decompose more quickly, and continue their natural cycle of giving back to the soil.

The pond in the garden of our childhood home was covered by oak leaves every autumn. These were cleared from the surface, to avoid overwhelming the pond and resident wildlife. Some leaves were left within the pond’s ecosystem to rot down as habitat for hibernating amphibians.

Leaves which fall to form a light covering over borders, or orchard areas, can be left. They will rot down and provide nutrients to the various plants around them.

I tend to leave the ones which fall across wilder areas of the garden. If they’re not smothering other plants, they will provide habitat for all sorts of residents. Including our prickly friend, whose thoughts will surely turn to hibernation before long.

With gardens, there really are no particular rules beyond using common sense, and trying to do the best for nature. We need more wild gardens, and fewer manicured lawns. As always, I find the Wildlife Trusts and RSPB excellent sources for information and ideas on creating natural havens. The Wildlife Trust gardening pages can be found here, and the RSPB have a similar section on their website.

Finally, with COP27 in session, we are reminded – again – of the devastating impact which climate change is having on our planet. The Royal Horticultural Society has a guide to things we can do within our own garden areas towards trying to slow the change. Whether that’s dealing with autumn leaves, or growing a rooftop garden, there’s something for all.