Leave the Leaves, a Landscape Expert Urges

“Leaving the leaves” is a landscaping practice that is growing in popularity as gardeners and homeowners become more eco-conscious and seek ways that they can work in concert with nature rather than constantly trying to beat it back.

Susan Barton, Ph.D., a professor of landscape horticulture and extension specialist at the University of Delaware, recently offered her tips for managing fall leaves in a way that is better for soil, plants and wildlife.

Leaves contain nutrients and organic matter, she noted. “When they are allowed to remain on the soil, whether it’s chopped up in the lawn or in a landscape bed, those nutrients are going back into the soil system to be taken back up by plants,” she said.

The decomposing organic matter improves the soil structure, which also is beneficial for plants, she added.

Better soil structure “allows water to infiltrate better and allows there to be more air present in the soil, which is important for plants,” she continued.

“So if you think about a forest system, of course, the leaves are just naturally recycled into a forest — and our forest soils are some of the richest soils that we have. So by allowing that same natural process to occur on your lawns, you’re getting a soil that’s more like a forest soil than a typical suburban lawn soil.”

Soil structure is probably even more important than the presence of nutrients, she said.

“A lot of people think the soil is just the mineral component — the sand, the silt, the clay — but soil is also about 50 percent pore space,” she explained. “If the structure is bad, those pores are very small and they’re completely filled with water. That’s how you get a waterlogged soil, which is bad for plants.”

When the pore spaces are large, about half fills with water and half fills with air, she said, adding, “and that’s a much better system for plants to grow in.”

The remaining 5 percent of healthy soil should be organic matter, such as decaying leaves, fungi, bacteria and earthworms — “all the other living things and decomposing things that would be in a soil system.”

When To Remove, or Move, Leaves

“You do have to remove the leaves from the lawn, because a thick layer of leaves would exclude light, which would not allow the lawn to photosynthesize — and grass needs to do that in order to grow and stay healthy,” Barton said.

One way to “remove” the leaves from atop the lawn is to go over them with a mulching mower so that the shredded leaves are fine enough that they sift down into the grass and decompose, returning nutrients to the soil.

“Or you can rake or blow them into a landscape bed that’s near the lawn,” Barton said.

When it comes to grass clippings, she said, there is no reason to remove them, and that letting them sift down back into the lawn results in reducing the need for nitrogen fertilizer by one-third.

“If you’re maintaining a really high-quality lawn, you might put about three pounds of nitrogen down per year per 1,000 square feet,” she said. “And you could put only two down if you recycle clippings.”

For leaves that have fallen elsewhere — say, under a tree or among shrubs — Barton discourages removing the leaves at all.

“The only reason to rake and bag is if you want to move the leaves to a different location in your landscape,” she said. “What I would really discourage is putting the leaves in a black plastic bag and putting them on the end of the driveway so they’re sent to a landfill somewhere, because then you’re getting rid of a resource and making it a problem as it fills up our landfills.”

Composting Here or There

The South Fork towns both have composting facilities where residents can drop off leaves, assured that they will not end up in a landfill. Residents also can pick up free compost made from discarded leaves and other yard waste.

“If you actually go back to that composting facility and get the resulting compost and use it as mulch for your garden, you’re accomplishing the same thing, only you’ve added transportation into the mix, which certainly could be a negative, environmentally,” Barton said.

Alternatively, residents may also wish to compost their leaves on their own property in a compost bin, tumbler or loose pile.

“You wouldn’t want a pile that’s more than about 4 feet tall,” Barton advised. “The lower the pile and the more spread out it is, the faster the decomposition will occur. And if you really want it to speed up, you could have a fairly low pile — like, maybe 2 feet tall — and you could run over those leaves with a lawnmower and chop them up. And then they’re almost immediately ready to get put back on the landscape as mulch.”

Rather than paying for hardwood bark mulch to be reapplied each spring in garden beds, Barton suggests using leaf mulch, at no cost.

“Leaf mulch is a beautiful mulch that is free and available to you if you have trees that shed leaves,” she said.

Benefits for Wildlife

Many species of insects that pollinate ornamental flowers and food crops, and serve as a food source for baby birds, overwinter in leaf litter.

“By allowing leaf litter to remain in landscape beds, you’re providing that overwintering space for insects,” Barton said. “A lot of people don’t immediately want to encourage insects in their landscape, but, really, only about 2 percent of the insects are considered pests. Most insects are either beneficial or of no consequence to humans, but they are very important for other members of the food chain, particularly birds. Birds feed their young with insects, predominantly caterpillars.

“So if you allow caterpillars to overwinter in your leaf litter, you’re providing food for birds that are going to hatch throughout the spring.”

Reducing Lawn

When a property is seemingly carpeted in wall-to-wall lawn, there are few places for leaves to fall where they won’t smother turf grass. Reducing lawn space by adding more plants or letting it turn into garden beds where leaves can accumulate will better serve wildlife than high-maintenance, pesticide- and fertilizer-intensive turf.

“Sometimes I hear from people, ‘Well, I just don’t have space. I don’t have that many landscape beds to accept all of the leaves that fall,’” Barton said. “And what I would say to them is to look at your landscape and think, ‘Where do I really want lawn?’

“Lawn is the only surface that we can walk on, so it becomes circulation in your landscape,” she continued. “It’s good for a play surface, and it’s good as a gathering space.”

Design those spaces into the landscape intentionally, and allow every place else to be something else, she instructed.

She repeated a message promoted by one of her University of Delaware colleagues, entomologist and native landscapes advocate Doug Tallamy.

“We need to provide ecosystem services in our suburban landscape,” she said. “We need better water recycling, we need cleansing of the air — all of those things used to happen in untouched forests that we just don’t have any more. And so the land that we have available to us is suburbia, and we can manage suburbia in a way that it provides those ecosystem services, but it’s going to provide them a lot better if you’ve got a ground cover, a shrub layer, a small tree layer, a large tree layer than it will if all you have is lawn.”

Replacing lawn with plants also reduces stormwater runoff that pollutes waterways. “Having landscape beds, trees and shrubs that break up the impact of the raindrops and allow water to infiltrate right there is so much better than having water runoff carrying pesticides and fertilizer and organic debris into surface water,” Barton said. “The best way to clean water is to have it filtered down through the soil. So when you allow water to run off the surface you are eliminating that natural process that cleans water.”

Barton is not against lawn. “That emerald green lawn, there’s nothing wrong with it. It should just be smaller and purposeful. And there should be much more interesting plantings around that lawn.”