As leaves across America make their annual fall pilgrimage from the treetops to the ground, lawn and wildlife experts say it’s better to leave them around than to put them in a bag.
First, because it keeps leaves out of landfills. Every year, about 8 million tons of leaves end up there.
And second, because the leaves help the grass.
The leaves are packed with nutrients, including nitrogen, phosphorus, and potassium.
“These nutrients are returned to the soil,” Susan Barton, a professor and extension specialist in landscape horticulture at the University of Delaware, told NPR. “But probably even more important than that is the organic matter. It’s the fact that you have this tissue that eventually breaks down and improves soil health.”
They also provide habitat for insects, spiders, slugs — and depending on where you live — possibly turtles, toads and small mammals, according to the College of Agriculture & Natural Resources at the University of Delaware.
In order to optimize your dead leaves, a little maintenance is recommended. It is better to go over a thin layer of leaves with a lawnmower or cut them in other ways so that they decompose more quickly. Thick layers of leaves are also bad for grass.
“If you just leave the leaves on the grass, it will shut out the light. And then the grass won’t be able to photosynthesise. Eventually it will die under a thick layer of leaves,” Barton said.
Collect excess leaves in a landscape bed and they will turn into mulch. Shredded leaves can also be piled in a garden.
“Ideally you want to let them break down a bit and they’ll make a really nice mulch. Instead of going out and buying hardwood bark mulch, which is expensive, you can have a better mulch that’s free,” said she declared.
At the same time, city dwellers should be aware that wind and rain can blow leaves onto the streets and clog drainage systems, creating a risk of flooding.
Some cities actually collect the leaves for composting at a central facility, where they turn into mulch that residents can collect for free. On the other hand, leaves in landfills that don’t have enough oxygen to decompose will eventually release a significant amount of methane.
How people treat leaves is only part of a longer-term issue of environmental sustainability.
“We want to look at these leaves as a resource,” not a problem, Barton said. “And when you think about sustainable landscaping, well, one of the things we say about sustainable landscaping is to let natural processes happen. And it’s a natural process.”