It’s easy to be nostalgic about autumn with its crisp clear skies, colorful trees and the unforgettable aroma of raked leaves burning in a neatly mounded pile. Norman Rockwell even immortalized the scene in his artwork.
Do you spot a problem in this walk down memory lane? First, most cities today would frown on lighting a match to a pile of leaves in the back alley, as we once did. Second, a beneficial natural resource, leaves, is going up in smoke. Third, there’s a good case for not raking at all — instead, simply mow the leaves back into the lawn.
Have you ever walked through a forest and noticed the richness of the forest floor, as fallen leaves over time have decomposed into a compost-rich soil? Leaves can similarly benefit our own yards, and there’s little need to meticulously sweep them from our lawn and landscape.
The concept is simple. Lawns become healthier if leaves are mulched back into the lawn with the mower, instead of raking them away.
Research initiated by Michigan State University in the late 1990s set the pattern for what has become the recommended norm from turf researchers and lawn care professionals for the past 20 years. The extensive study by MSU showed that leaves pulverized back into the lawn with a mower created a healthier lawn versus removing the leaves. Time has proven the research correct.
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Lawn areas where leaves were mulched were healthier than lawn areas 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.”
MSU’s findings made great impact on autumn lawn care. Their studies showed that homeowners can achieve a remarkable 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 even 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 or only barely moist, 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.
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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, University of Minnesota, North Dakota State University, Consumer Reports and even Bob Vila.
The Scotts Co., known for their lawn products, advocates the process also. “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.
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.
