Did you hear about the guy who doesn’t believe in repeating gossip, so you need to listen closely the first time? I don’t repeat many of our gardening columns from year to year either, unless it’s with a new twist, new research — or it’s a topic that’s proven popular.
Today’s topic has generated more interest in past years than even tomato blight. The thought of never raking leaves again is welcome news for many lawn owners.
The concept is simple: Lawns become healthier if leaves are mulched back into the lawn with the mower, instead of raking them away.
Surprisingly, mowing over fallen leaves and letting them remain is great for the lawn, and there’s research to prove it. In the late 1990s, Michigan State University wanted a research-based answer to the question of whether it’s better to remove leaves from the lawn or pulverize them back in. During the extensive three-year study, scientists considered three different leaf layer thicknesses: none, 3 inches and 6 inches of mixed tree species, mulched in with a rotary mower every October.
In summary, mowing leaves back into the lawn proved beneficial for turf health. Lawn areas where leaves were mulched were healthier than the lawn area receiving no pulverized leaves. MSU concluded, “Research clearly indicates that mulching leaf litter into existing turf grass provides benefits for the soil and turf grass plants by adding nutrients, retaining soil moisture, loosening compaction and reducing weed growth.”
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MSU’s findings have made great impact on autumn lawn care. Their studies showed that homeowners can achieve a nearly 100% decrease in dandelions and crabgrass by mulching autumn leaves for three years, as the shredded leaves cover up bare, weed-prone spots between grass plants. Mulched leaves keep the turf’s soil warmer in winter and cooler in summer. Mulched lawns green up faster in spring, with less fertilizer needed.
Researchers at MSU suggested using a rotary mower that pulverizes leaves well, such as a mulching mower or a mower with the discharge opening covered, and with the mower height adjusted to a high setting. Leaves should be dry and mowed slowly with a sharp blade to grind leaves fine. If leaves are still in large pieces, go over the lawn again at right angles to the first pass.
The optimum time to mulch the leaves is when you can still see some green grass through the fallen leaves, rather than letting the leaves gather too thickly.
Pulverized leaves should settle into the turf within a few days, and remaining leaf litter shouldn’t be allowed to cover grass blades entirely. If leaves accumulate in a layer too thick to mulch, an option is to rotate by raking or bagging one week, then mulching the next.
The beneficial effects of mulching leaves back into the lawn are most noticeable after following the practice for several years. Leaves are a natural soil-builder as they decompose. Besides MSU, mulching leaves is advocated by Purdue University, the University of Minnesota, North Dakota State University, Consumer Reports and even Bob Vila.
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The Scotts Co., well-known for its lawn products, also advocates the process. “Take the grass catcher off your mower and mow over the leaves on your lawn. You want to reduce your leaf clutter to dime-size pieces. You'll know you're done mowing leaves when about half an inch of grass can be seen through the mulched leaf layer. Once the leaf bits settle in, microbes and worms get to work recycling them. When spring arrives, the leaf litter you mulched up in the fall will have disappeared.”
Don’t let unmulched leaves lay on the lawn over winter, as they can smother grass. If your yard has too many leaves to mulch into the lawn, you can put the bagger attachment on, collect the leaves and spread the mulch on flower beds and gardens, incorporating it into the soil. Microorganisms will break down the organic materials, improve soil health and release nutrients. Mulched leaves will biodegrade and disappear by spring.
Well, there you have it. Raking leaves may soon be relegated to nostalgia and Normal Rockwell prints. I will admit, though, I miss the autumn aroma of a burning leaf pile.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu or call 701-241-5707.
