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Helping Trees While Saving Your Lower Back
By Martha S. Hill
Autumn brings the magic of vivid colors (yellows, oranges, and reds of every shade) but as leaves fall, visions shift to backaches and blisters from creating big piles of leaves to cart away. Have we perhaps misinterpreted the message written by the trees in their colored leaves, creating more work for ourselves to boot?
Research suggests people do trees no favor by raking fallen leaves into piles and carting them away, especially when part of the journey includes driveways and streets laden with oils, tars, and other pollutants.
Turf and horticulture experts tell us to stop carting away piles of leaves (a behavior some liken to strip mining ) and to start leaf mulching instead (with less labor in the process!).
Seeing the forest for the trees
In ecological systems that have evolved over eons, trees use their leaves to play key roles providing valuable gifts.
By their very presence, trees are shade (welcoming in hot summers) and umbrella (has a tree befriended you with cover in a sudden rain shower?).
Behind the scenes, trees are wizards. With alchemy of sorts, they use their leaves to create oxygen, purify the air, moderate temperatures, and build nutrient-rich soil. Through photosynthesis, trees take into their leaves the carbon dioxide we have breathed out or pumped into the air by burning fossil fuels, separate the carbon and oxygen, and return the oxygen to the air we breathe. Trees also cleanse that air of toxins (nitrogen oxides, ammonia, sulfur dioxide and ozone) using leaves and bark to trap particulates. Trees cool the environment not just with their shade but also by pumping water from the soil and, through their leaves, releasing it into the air as water vapor. From the air and deep in the earth, trees draw minerals and nutrients into their leaves and branches. By falling to the ground, and with a little help from spent grass blades and soil organisms (molds, bacteria, earthworms and beetles), the discarded leaves and branches are transformed into topsoil and humus -- riches for plant growth in future years.
Fallen leaves contain 50-80% of the nutrients drawn from the soil and air during the growing season , yet, each fall, we cart those nutrients away (and make more work for ourselves by doing so!) With leaf mulching, we leave the leaves there to nourish our woods, backlots, and lawns.
Leave the leaves!
Mulching involves spreading organic matter in a thin layer on the ground to decompose in a natural cycle. Leaf mulching uses a rotary power mower to shred leaves on the ground into small pieces. Leaf mulching:
- Makes nutrients more readily available in the soil and speeds up the soil-enrichment process
- Retains water in the soil during the summer, for drought protection
- Insulates the ground from penetrating cold during the winter, allowing the underground work of earthworms and soil microorganisms to continue the processes of creating humus
- Helps reduce weeds
- Supports many parts of the ecological system better than bare ground or course bark mulch (by providing appropriate cover, for example, for night-feeding caterpillars that need daytime protection from predators)
How do lawns respond? Experts at Michigan State University, Purdue University, and Cornell University have researched influences of leaf mulching on lawns from many perspectives -- turf’s visual quality and growth, soil pH and nutrient availability, thatch formation, and disease and weed infestation -- and these experts endorse leaf mulching.
When done as part of regular lawn-mowing, mulching requires little added labor or fossil fuel use and saves all the backache, blisters, and time associated with the pile-and-cart-away approach. It’s not hard, and it keeps beauty in your trees and lawn. To start mulching this autumn, see the expert tips at (left/right).
Martha Hill is a Sierra Club member and volunteer who encourages you to “leave the leaves!”
She thanks Murdo Morrison of The Garden Bench
for the timely photographs of leaf mulching and excellent source writeup.
References:
i. Goatley, Jr.; Purdue University Consumer Horticulture; The Agriculture Program of the Texas A&M University System; and Belt.
ii. Montgomery County, Maryland, Department of Environmental Protection
iii. TreePeople
iv. The Agriculture Program of the Texas A&M University System
v. Dole
vi. Goatley, Jr.; and Reicher and Hardebeck.
You can do it! Here’s how.
Leaf Mulching 101 – Tips from the experts
- Do leaf mulching in stages throughout autumn to avoid leaves piling up too thickly.
- Do leaf mulching when leaves are relatively dry, to prevent clumping of leaves.
- Rake the leaves relatively evenly over the lawn, creating no more than about a 1-inch carpet of leaves.
- The most effective mower is a mulching mower (a lawnmower with a special mulching blade and a plate covering the side opening). Most mowers sold in the last 10 years are mulching mowers, and kits with a mulching blade for retrofit are available at hardware and garden stores.
- Set the mower to a three-inch height.
- If the mower has a side discharge chute, you probably want to begin on the lawn’s outside perimeter, blowing chopped leaves onto unmowed areas and continue mowing inward. This keeps leaf particles on the lawn and allows you to mow over them a few more times.
- Mow slowly, being sure to give the mower blades time to shred the leaves.
- If a first mowing leaves a significant amount of whole leaves, mow the area a second time (perpendicular to the first direction) and a little slower.
- If your mower has a bagging attachment, you might collect some of the leaf mulch and apply it after the first hard freeze (and up to about a 2-inch depth) over bare spots, around trees, shrubs, perennial beds, or herb gardens, to encourage healthy growth.
- As always, think safety whenever mowing your lawn: pick up branches beforehand, watch for animals and plants within range of the discharge of the mower, and consider safety goggles for safeguarding eyes, an air mask if leaf dust is of concern, gloves, and heavy clothing.
- Sharpen mower blade and change air filter more often when mulching thick layers of leaves.
- Admire your work! Leaves are left in small pieces evenly on the lawn, and little leaf is visible from a distance.
- Enjoy the magic colors while you are leaf mulching!
Lawn services will mulch, too. If you use a lawn service, tell them you’re interested in making the switch to mulching.
Other resources
The Agriculture Program of the Texas A&M University System, Extension Horticulture Information Resource
Belt, Louise M. “Autumn Leaves: Myth & Reality.”
Dole, Claire Hagen. Inviting Caterpillars Into Your Garden
Fosdick, Dean.
“Mulch leaves rather than rake them”
Goatley Jr., Mike. Nov. 2004 “’Leave’ Them Alone: Lawn Leaf Management”
McNelly, Jim. 2000 “Mulching: Nature’s Composting Secret”
Montgomery County Maryland Department of Environmental Protection “Turning Autumn Leaves into Healthy Lawns”
Morrison, Murdo. “Taking Care of Leaves with a Mulching Mower”
Nikolai, Thomas A. “When leaves turn to litter”
Pollan, Michael. 1991 Second Nature: a gardener’s education. New York: The Atlantic Monthly Press.
Purdue University Consumer Horticulture, Much Ado About Leaves.
Reich, Lee. (Jan.-Feb. 2005) ‘Simply Soil: The soil in winter,’ Fine Gardening No. 101: 72-73.
Reicher, Zac and Hardebeck, Glenn. Aug. 1, 2000. “Mulching tree leaves: an alternative to disposal”
Reicher, Zac and Hardebeck, Glenn. 1999. “Leaf Mulching Effects on Turf Performance”
TreePeople. ‘Get Involved; Why Trees?’
York Region. “Leaf Mulching”
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