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Ask the Expert: Doug Tallamy Explains Why (and How to) Leave the Leaves

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Ask the Expert: Doug Tallamy Explains Why (and How to) Leave the Leaves

November 1, 2023

As leaves fall and the call to “leave the leaves” rises—from major news outlets to your next door neighbor—you may find yourself scratching your head as to how, exactly, to leave the leaves.

The slogan is a fun way to get people to consider a serious problem. We are in the sixth great extinction event in the history of the earth, which is directly affecting our food web. When one species goes extinct or its population declines severely, it can have a negative ripple effect on other species and the ecosystem as a whole. How does this tie into leaving the leaves in your own backyard? How does it help? And how do you do it?

Doug Tallamy can explain. He is an entomologist, a conservationist, and a professor in the Department of Entomology and Wildlife Ecology at the University of Delaware. He’s even written a book, Nature’s Best Hope, which is a blueprint for saving the earth one backyard at a time. (It’s on Gardenista contributor Melissa Ozawa’s list of favorite gardening books: see In Gratitude: How a Gift from a Boss Led to a Love for Gardening Books.) Below, Doug gives us the low-down on leaving the leaves.

Photography by Joy Yagid.

Q: Why do you think people don’t leave the leaves?

We&#8\2\17;ve been conditioned to think that we have to clean up the leaves, but fallen leaves are not only beautiful, they help the soil.
Above: We’ve been conditioned to think that we have to clean up the leaves, but fallen leaves are not only beautiful, they help the soil.

A: We do what we observed when we were kids. It’s been part of our culture to get rid of the leaves. You either burn them or you put them out in the curb for the city to take away, but you have to take them off your lawn and do something with them.

Q: What’s the easiest way to start?

A: Well, there is a conflict between having that perfect lawn and and the leaves that fall on the lawn. So people say “I gotta get the leaves off the lawn.” [The solution is to reduce] the area you have in lawn. The perfect way to start doing that is to create beds under the trees that you have. And you do that by raking the leaves into those beds. And in the beginning when you’re trying to actually smother the grass, [to make the beds] you rake a lot of leaves, you make it pretty thick. My son bought a house and the first fall, he called me up and said, “Dad, I got too many leaves. What should I do with them?’” I said: “Put them in your flower beds.” He said: “I don’t have enough flower beds.” I said: “Exactly.” You increase the amount of flower beds and that’s where the leaves go. The extra ones that just don’t fit in those flower beds can go into a compost heap.

Q: Does it matter what kind of leaves you have? What are the best leaves for this?

Leave the leaves around a tree. They will provide valuable nutrients as they break down.
Above: Leave the leaves around a tree. They will provide valuable nutrients as they break down.

A: Oak leaves. [They] break down slower. So, that’s their main benefit. You never want to have bare ground. Maple leaves, tulip tree leaves, and birch—they all break down really quickly, so if that’s your leaf base, you’re going to have bare soil before the end of July and then your soil community really suffers. This is where oak leaves become important. One of the ecological benefits that leaves provide is to make a blanket on the ground that keeps the humidity and moisture in the soil because everything that lives in the soil requires high moisture levels. This includes the mycorrhizae and all of the creatures that are breaking down those leaves. They all require high humidity. It’s funny that people rake up the leaves, and they go out and they buy bark mulch…

The other major thing that leaves are doing is transferring the nutrients that your tree used that year into the soil so that they get to use it again. If you rake those leaves away, you’re slowly starving your trees and all the rest of your plants because you keep throwing away the nutrients. Most people don’t fertilize their trees and it’s hard to do it properly. It’s easy to over-fertilize them. So the very best thing is to keep all the leaves that fall on your property, and they should be as close to the trees as possible so that they can break down and provide the nutrients that that tree needs.

Q: How does one deal with an HOA or municipal regulations about lawns?

If you want to help your lawn (not get rid of it), mow the leaves in place (several times if necessary to get them small enough) and leave the pulverized leaves on the lawn.
Above: If you want to help your lawn (not get rid of it), mow the leaves in place (several times if necessary to get them small enough) and leave the pulverized leaves on the lawn.

A: Well, the lawn you keep is going to be mowed. It’s going to be manicured. That’s the way you edge those new beds you’ve created. So it looks nice and neat. [In the leaf beds around the trees that you’ve created], the perfect mulch is green mulch. So you actually want to plant through the fallen leaves. You want ground covers like ferns and May apples, wild ginger, and goldenseal—all kinds of spring ephemerals. That’s what should be under your trees. The leaves are nestled in there. Then it becomes a beautiful garden. But you’ve still got that mowed strip of grass surrounding that, and it’s neat and your HOA says, okay, you are taking care of your property. That’s all they care about. There’s no conflict.

How to “Leave the Leaves”

  1. To reduce your lawn, rake a thick layer of leaves onto areas where you want to smother grass and create a new bed for natives instead (e.g., around a tree).
  2. To help your already existing garden beds, move leaves off your lawn and onto the beds. They will act as both mulch and, as they break down, compost.
  3. To help your lawn, mow fallen leaves (a few times to chop them into small bits) and rake them back onto the lawn.

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Frequently asked questions

Why should I leave leaves in my garden?

Leaving leaves in your garden is beneficial for several reasons. First, they act as a natural mulch, providing insulation for the soil and helping to retain moisture. Second, as the leaves break down, they release valuable nutrients into the soil, improving its fertility. Lastly, leaving leaves in your garden creates habitat for beneficial insects, such as butterflies and beetles.

Will leaving leaves attract pests or promote diseases in my garden?

Leaving leaves in your garden does not necessarily attract pests or promote diseases. In fact, many beneficial insects rely on leaf litter as a food source and habitat. However, it is important to properly manage the leaf litter by shredding or mulching them to accelerate decomposition, as thick layers of unshredded leaves can create a moist environment that might harbor certain fungal diseases.

How do I incorporate leaves into my garden?

There are several ways to incorporate leaves into your garden. You can rake them into planting beds to act as mulch, spread them around trees and shrubs, or create leaf piles in undisturbed areas of your garden. Shredding or mulching the leaves is recommended to speed up decomposition. Additionally, you can also add leaves to your compost pile to create nutrient-rich compost for your garden.

Can I leave all types of leaves in my garden?

In general, you can leave most types of leaves in your garden. However, it is preferable to avoid using leaves from trees or plants that are known to be invasive or potentially carry diseases. Also, leaves from certain trees, such as walnut trees, contain chemicals that can inhibit the growth of other plants, so it's best to avoid using them if possible.

When is the best time to leave leaves in my garden?

The best time to leave leaves in your garden is during the fall season when trees naturally shed their leaves. You can start incorporating the leaves into your garden immediately or wait until they have completely fallen. Leaving them in the garden during winter and early spring provides beneficial insulation for plants and soil, while allowing them to decompose gradually.

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