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Autumn is the season of raking and bagging leaves – or is it? Some cities, environmental groups, and government agencies are encouraging homeowners to leave their leaves alone.
On Thursday, October 19, 2023, SciLine interviewed: Dr. Susan Barton, a professor of plant and soil sciences at the University of Delaware. She discussed topics including: why mulching leaves (or just not doing anything to them) instead of removing them can benefit lawns and gardens; additional reasons not to bag leaves, including keeping them out of landfills, reducing the resources needed to haul leaves away, and benefits to wildlife; and other evidence-based advice for fall lawn care, including when and how to fertilize lawns to minimize runoff that can harm local waterways.
SUSAN BARTON: My name is Sue Barton and I am a professor at the University of Delaware and I study sustainable landscaping.
Interview with SciLine
What are the benefits for lawns and gardens of mulching leaves instead of removing them?
SUSAN BARTON: The leaves contain nutrients and they also are a source of organic matter. So, if you allow the leaves to go back into the landscape, you are providing nutrients for plants to take up and you are providing organic matter that will improve the soil structure. So, if you think about a forest soil is where leaves are just naturally returned to the soil and decomposed every year—it’s some of the richest soil that we have—and so by allowing that to happen in your landscape beds, you are getting the benefits that you would get in a forest soil.
Can leaves that fall on a landscaped property ever be left as they are, or should they always be mulched?
SUSAN BARTON: When the leaves fall on a lawn, we have to rake them up off of the lawn or chop them up with a lawn mower so that they are finer and can sift down in through the grass blades, because grass needs light to photosynthesize and grow. And if we have a layer of leaves on the lawn it will exclude light and that would be detrimental to the lawn. If they fall in a landscape bed, depending on the ground cover that’s under them, which is usually trees and shrubs and larger plants, it’s fine to just leave the leaves without mulching them.
What can be done to keep leaves from blowing from one property to another?
SUSAN BARTON: Chopping up the leaves will dramatically reduce the blowing of the leaves. So, if you get them to be smaller—and that could happen either by mowing over the leaves where they fall in the lawn, or you could rake them into a pile and then mow them up in the pile. There are also vacuums, leaf vacuums, that you can purchase where you can vacuum up the leaves and they’ll chop them up and put them in a bag and then you can take the leaves from that bag and spread them on your landscape beds. But of course, the easiest thing to do is chop them up with a lawn mower. And you wouldn’t want to do that in a six foot deep pile, but about two feet deep you can mow over leaves with a lawn mower that way.
What are the environmental benefits of not removing leaves from a property?
SUSAN BARTON: The leaves are really a resource when we allow them to be recycled into our landscape. If you rake up your leaves and put them in a black plastic bag at the end of your driveway and they’re taken off to a landfill, they then are taking up space in a landfill and they never get to decompose and return those nutrients and organic matter back to the soil. So, you’re taking what could be a resource and making it a problem that’s filling up the landfill. Also, many insects overwinter in leaf litter and so by allowing the leaf litter to stay in your landscape beds, you’re providing an opportunity for overwintering insects. And a lot of people might immediately say, well, I don’t really want insects in my landscape anyway, but only about 2% of all the insects in the world are considered pests. Most of them are either beneficial or of no consequence to humans, but they are very important sources of food for other animals like birds. Birds feed their infant birds insects, especially caterpillars. And so by allowing the insects to overwinter in the leaf litter, you’re supporting bird populations and of course, you’re also supporting pollinators, which we all need for crops and just for the seed development of most plants.
When should people fertilize lawns?
SUSAN BARTON: The lawn should be fertilized in the fall because that is when turf grass is primarily growing roots and the shoots like tillers, which are small plants that are produced right next to an existing plant, and stolons and rhizomes, which are either underground stems, rhizomes, or above ground stem, stolons. And that’s how lawn grass is spread. So, all of that is being done in the fall. And so when you fertilize in the fall, you’re promoting that kind of grass growth that makes a healthy, dense lawn. When you fertilize in the spring, your grass is growing leaves at that point, so you’re really just causing the grass to grow more, grow faster and that’s what we have to cut off regularly. So, it really doesn’t make sense to fertilize in the spring. When you chop up the leaves that fall, you are actually also fertilizing in the fall because you’re putting those chopped up leaves back into the soil. It is a good idea for a well maintained lawn to add some additional fertilizer besides just the leaf litter.
How can people get the most out of their lawns and make their landscaping more environmentally friendly?
SUSAN BARTON: The suburban norm is to have lawn first and then put in some decorative plants around the house or at the end of the driveway or wherever people sort of typically put plants. And I think if you sort of flip that paradigm, and you say alright, I’m going to design my lawn. I’m going to design areas of lawn that provide for circulation and play and gathering spaces and I’m going to make them a particular shape that I really like and then figure out what everything else can be. It’s just a different way of thinking about the landscape and it is much more environmentally sensitive, and will provide all kinds of ecosystem services, whether it’s better water infiltration, better air quality. If we think about pulling carbon dioxide out of the air, we’re doing it a lot more if we’ve got a ground cover, a shrub layer, a small tree layer, and a large tree layer than we are if we have just the surface of lawn.
What advice do you have for reporters covering fall leaf management?
[Posted October 19, 2023 | Download video]