Stop Raking Leaves This Spring and Keep the Carbon in Your Soil

Tempted to take your spring cleaning outside? Instead, save your energy (and improve your soil’s health) while letting your messy yard fight climate change.

New University of Maryland research found that in places where people let their fallen leaves decompose without removing them, the soil holds up to 32% more carbon, which otherwise could be released into the atmosphere as a greenhouse gas through yard waste burning or rotting in a compost pile. The paper was published in the journal Plants, People, Planet.

Lead author Max Ferlauto, a Ph.D. candidate in the Department of Entomology, was studying how removing fallen leaves affects insects during the winter when he began to wonder about soil carbon.

“Soil is one of the main ways the earth stores carbon, but there hadn’t been any studies looking at the effect of removing fallen leaves on soil carbon function in suburban yards and urban areas,” he said. “What we show in this study is that removing leaves reduces both the carbon and the nutrients in the soil, and that changes the ability of the soil to perform fundamental ecosystem functions.”

About 35 million tons of grass clippings and fallen leaves are removed annually from urban and suburban landscapes, according to the Environmental Protection Agency. Scientists have estimated that in Minneapolis, 11% of residential carbon output is due to yard waste removal, and in Boston, about half the carbon that falls to the ground in leaves is removed from the city.

Carbon is essential for healthy soil. It provides structure, makes the soil more fertile and enables it to hold more water during storms, decreasing runoff. Soils depleted of carbon need more chemical fertilizers and more frequent watering to support a green lawn. And when it rains, more of the rainwater runs off into nearby waterways, carrying those chemicals with it.

To conduct his study, Ferlauto set up test plots in 13 suburban yards between Washington, D.C., and Baltimore. In each yard, he marked off one 2-by-1-meter plot in an area that had been cleared of leaves for many years, and one where leaves had been allowed to accumulate, such as behind a shed or along a tree line.

Ferlauto and his team, which included entomology Assistant Professor Karin Burghardt and postdoctoral associate Lauren Schmitt, divided each plot in half with mesh. In the fall, they cleared fallen leaves from just half, and in the spring, they analyzed the soils in each plot, repeating the experiment for two years.

One of the study's key findings was that leaving fallen leaves on previously raked lawns for those two years was insufficient to restore depleted soils. Within each test plot, the cleared and uncleared halves showed no measurable difference in either soil carbon or the decomposition rates of the leaves. But there was a big difference between test plots in different locations of the yard. Areas where fallen leaves had been regularly left to accumulate had 21% faster decomposition rates, and up to 32% more soil organic carbon compared to areas where leaves were regularly removed.

Ferlauto suggests that people who want to improve soil carbon and the health of their yard’s ecosystem should consider the purpose of a lawn. Cleaning up fallen leaves may make sense for those who have children and pets who use the backyard. But people who don’t use their yards much may consider clearing only the front yard, or turning green space into meadow or a more natural forest floor environment with native plants such as ferns and other species adapted to grow in areas with a leaf layer.

Acknowledging that not everyone can or wants to leave fallen leaves on the majority of their lawn, Ferlauto encouraged people to find spaces to intentionally let leaves lie, like along fence or tree lines, or even moving leaves from lawns into garden beds or beneath trees.

“I’m a big advocate of ‘do what you can, where you can,’” he said. “It doesn’t have to be all or nothing.”