Every fall, my husband does his best to avoid raking leaves. He checks our huge silver maple tree daily. And as soon as the leaves start coming down, he gets out the mower. His theory is that chopping leaves with the mower is much easier than raking and bagging them. So he mows several times and allows the chopped leaves to stay on the lawn. It turns out that he hasn't been lazy all these years, he's been right.
New research from Michigan State University shows that chopped leaves left on the lawn not only add organic matter and nutrients, but they also may have compounds that suppress dandelion seed germination.
The research was done on Kentucky bluegrass lawns (the grass most of us have in our lawns) and used a standard rotary mower, but was limited to chopped maple and oak leaves. Still, the results were clear and striking: Bits of leaves can improve spring green-up and reduce dandelions. (To read the report, go to horttech.ashspublications.org/cgi/content/abstract/19/2/297.)
Previous research already showed that chopped leaf mulch had no negative effects on grass. (Specifically, it didn't reduce turf density or shoot growth, didn't add to thatch accumulation or change the pH level.) But the new research indicates that it's actually beneficial to chop your leaves and leave them on the grass, as long as you can still see the grass. That's the key.
Chopped leaves filter down into the soil, where they can do good. Whole leaves can mat down and cover the grass, which can suffocate lawn grasses and kill them. So you're not entirely off the hook when it comes to fall lawn care.
Bottom line: You may not need to rake your lawn, unless you have a very thick layer of leaves on it. But, if you don't rake, you do need to run the mower over the leaves on the lawn several times until you can see the grass through the chopped leaves.
Here are a few more fall lawn care tips:
• Try to remove leaves at least once a week during the fall. If you can't see the grass, it can't grow. And grass does continue to grow in fall.
• Don't leave piles of leaves uncollected on the lawn. Move them to the compost pile.
• You can allow some leaves to remain under trees (as in a forest) or scatter leaves in the wooded areas of your property as long as the leaves are 4 inches or less in depth.
Mary Hockenberry Meyer is a professor and Extension Horticulturist with the University of Minnesota.