Piet Oudolf once told me: “Americans like to display their mulch.” He’s not wrong, sadly.
Mulch is part of our garden aesthetic. Is it a lack of imagination? A nefarious scheme to lower the required training of landscape staff? Whatever the reason, I’m so grateful it’s changing.
Gardeners all over the world are developing strategies to encourage biodiversity in our landscapes. The rewilding movement is spreading and naturalistic gardens are seeding in everywhere. But even people who prefer more formal or floral gardens can incorporate practices that invite in wildlife. A big part of that work starts with mulch, leaves and soil.
The very top of the ground, where leaf litter breaks down into humus, is an incredibly rich ecological zone that gardeners often unknowingly remove. That zone, the ‘duff layer’ in ecological parlance, is necessary habitat for many of the animals we love, as well as one of the main techniques that plants
use to create the soils they want to live in.
Gardeners like to garden. But wildlife tends to thrive in areas we leave alone
In autumn, when tree leaves fall to the ground, they aren’t being thrown away. Trees are carefully placing those leaves over their root systems where they insulate the soil and hold in moisture. Worms will pull leaves deep into the ground where carbon is sequestered. Fungi and bacteria will break them down until micronutrients are cycled back into plant-available forms. As leaves, twigs and other plant materials biodegrade, they create the soils that those trees prefer. It’s terraforming. Some gardeners have it backwards: we’re not making soil for plants – the plants are making it for themselves.
Many animals have come to rely on that duff layer. Bumblebees will overwinter just underneath those leaves, in the soft soils of northern slopes. Many moths and even a few butterflies spend part
of their lives in the leaf litter, sometimes as eggs, sometimes as caterpillars, but most often they fall down from trees, descending on silk threads, into the leaves to pupate into adulthood. If you have an oak, there’s a solid chance you also host purple hairstreak butterflies, who spin their cocoons under fallen oak leaves. The charming pink of the elephant hawk moth emerges from a dull brown pupa, camouflaged to blend in with the leaves they hide out in.
Insects such as beetles and woodlice who play critical roles in larger food webs often rely on the structural complexity of that leaf layer to hunt and hide. When we make more habitat for insects, we invite the birds who rely on them into the garden as well.
None of this is to say you should let leaves smother your lawns
When you rake that away, you’ve raked away a bunch of animals. And for what? To compost the leaves, then replace them as mulch? Why not leave them alone?
In the USA, there’s a popular movement to ‘leave the leaves’. They’re literally called leaves – we should leave them. Of course, leaving leaves can look a bit wild, perhaps unkempt. In more formal environments, there are strategies to give a clean look. Often, we remove the first foot or two of duff along the front of a garden bed, and make a clean line of mulch. These ‘cues to care’ make a garden look tidy and let people know they’re intentionally naturalistic. Keep a clean edge, and you can get away with benign neglect in the rest. We call it the ‘garden mullet.’
Gardeners like to garden. But wildlife tends to thrive in areas we leave alone
None of this is to say you should let leaves smother your lawns. Leaves on lawns can be mulched in with a mower. Thicker leaves, or those that fall in massive amounts can be thinned and moved around the landscape. Some of our common garden plants will grow happily through leaves, while others will faint dead away if four leaves get near them. There’s a bit of a learning curve, but it’s worth it. These practices are becoming more important as we watch insects disappear and bird populations decline. The more our gardens mimic the natural environments these plants and animals evolved to inhabit, the better we can co-exist.
Gardeners like to garden. But wildlife tends to thrive in areas we leave alone. Often the biggest hindrance to biodiversity is we well-meaning gardeners. But we don’t have to be. Like plants, we can grow and adapt. We can learn to accept a bit of wildness.
Many of the strategies we hear of to address climate change and biodiversity decline require action – this one requires you not to act. Maybe sit in your garden and have a glass of wine. Watch the sun set. And get to know the animals who share your land with you.
Rebecca McMackin is an ecological horticulturist based in New York.