Many people and organizations these days are looking for ways to reduce excess carbon dioxide in the atmosphere, in the hope that this might slow the warming of the planet. Even the turf industry claims that “well-managed” lawn absorbs carbon and thus should be considered a good thing.
“Lawn is a valued resource for sequestering carbon, with a net positive carbon storage for all lawn management practices.” That’s what they say at Scotts Miracle Gro, which calls itself the world’s largest marketer of branded consumer lawn and garden products.
Both the Lawn Institute and the Outdoor Power Equipment Institute (who knew there was such a thing?) echo this opinion. Ditto for countless lawn product wholesalers and retailers across this country who are eager to proclaim this newly-discovered virtue of the American lawn.
Yet… is it true? This claim appears to be based on a single research report: “Technical Assessment of the Carbon Sequestration Potential of Managed Turfgrass in the United States.” This report was prepared by Dr. Ranajit Sahu in 2008, at the request of the Outdoor Power Equipment Institute. (hmm)
Before going further, we need to be clear about some basic concepts:
- As the EPA defines it: “Terrestrial carbon sequestration is the process through which carbon dioxide from the atmosphere is absorbed by trees, plants and crops through photosynthesis, and stored as carbon compounds in biomass (tree trunks, branches, foliage and roots) and as organic matter in soils.”
- A carbon sink is any system that stores more carbon molecules than it releases.
- A carbon source is any system that releases more carbon molecules than it stores.
Let’s assume that Dr. Sahu’s data are accurate and that in fact “well-managed lawns capture four times more carbon from the air than is produced by today’s typical lawnmower.” According to Sahu and the turf industry, a well-managed lawn is one that gets mowed regularly, treated with chemicals and watered as needed to keep it growing vigorously. So, let’s take a closer look at this whole system.
How much carbon is actually stored in lawn?
Sahu’s report combines data from several studies to produce this averaged result (stated on page 12, if you’re looking for it): one acre of managed turfgrass will hold about 1.03 Mg/ha/yr. In regular language, this is 0.46 tons, or 920 lbs. of carbon in a year.
How much carbon do mowers emit?
This is the only kind of emission that Sahu includes in his calculations. Citing a “Major Equipment Manufacturer” and the World Resources Institute, Sahu concludes that the average amount of carbon emitted from a mower is 0.08 tons, or 160 lbs. per acre per year. So… 920 lbs. sequestered, minus 160 lbs. emitted by mowing, equals 760 lbs. of carbon storage. And voila…a carbon sink! Could this be the end of the story? No, it is not.
What about lawn chemicals?
We all know that some amount of CO2 is emitted in the manufacture and application of lawn chemicals. How much? Sahu admits that his report does not “evaluate indirect carbon impacts such as due to creation and transportation of the fertilizer necessary for the management of turf.” Apparently, in his mind, this is a minor point. He does footnote, though, a study by NASA’s Christine Milesi, which says carbon emissions due to fertilizer inputs range from 11-28 percent of the total sequestration potential. If we use the mid-point of that reported range, say 20 percent, we can estimate that another 184 lbs. of carbon should be subtracted from the total. This is more than the carbon emitted from mowing! And it brings our theoretical carbon sink down to 576 lbs.
And watering?
Well-managed lawns must also be watered. Why? Because fast-growing lawns need to be mowed often, and the resulting grass clippings, when left on the surface to decompose, will increase soil carbon. (Another Milesi study shows that without these grass clippings, carbon sequestration is dramatically lower. Yet consider: how widespread is the belief that removing the clippings is actually best for the lawn.)
Anyway, irony aside… how does irrigation factor into the equation? The carbon emissions from obtaining clean water are tricky to figure out. Luckily for us, planners in Portland, Oregon have conducted a detailed audit of that city’s water budget, and they conclude that their production of potable water emits 0.01 lb. of CO2 per gallon of water. Portland’s water supply is partly gravity-fed, so communities that rely entirely on pumped water would likely emit more CO2 than Portland. To be on the safe side, though, let’s use this conservative figure of 0.01 in our calculations.
Hang in here with me now, while we work our way through a few more figures. We are commonly advised to give lawns one inch of water a week. On an acre of lawn, this equals 27,154 gallons of water. Let’s say we irrigate our theoretical acre only six times a year (an arbitrary number, on the low side between “never” for some lawns and 15-20 times a year for others). This rather infrequent watering consumes almost 163,000 gallons per year.
Multiplying this amount of water by 0.01 (from the Portland audit), the CO2 emissions amount to 1,630 lbs. per acre. Because 1 lb. of CO2 equals 0.28 lbs. of carbon, this is equivalent to 456 lbs. of carbon molecules emitted due to occasional irrigation.
We are now down to a theoretical carbon sink of 120 lbs, in a whole acre of lawn.
To put this in perspective…
An acre of established temperate forest can hold from 2,000 lbs. up to 6,000 or more lbs. of carbon per year, depending on the age of the trees and other conditions. Mature grasslands sequester 2,400-3,600 lbs. per acre each year. And, except through natural disturbances (decay, fire, etc), these ecosystems emit only small amounts of CO2, when they respire at night.
Surely we can do better than a meager hundred-pound carbon sink in our managed landscapes. And this is not even the whole story. Sahu’s calculations, and the turf industry’s proclamations, also fail to account for:
- CO2 emitted by the manufacture and distribution of relentlessly marketed mowers, blowers, trimmers, edgers, shredders, clippers, sprinklers and sprayers.
- The carbon emissions of lawn care companies lugging their equipment all over town, day after day throughout the growing season.
- The emission of nitrous oxide – a greenhouse gas that is 300 times more heat-trapping than carbon dioxide – which results from using nitrogen fertilizers, an essential in “properly-managed” lawn.
So: is lawn a carbon sink?
Clearly, with all these factors in mind, there is no way that conventional lawn – lawn treated with pesticides, herbicides and fertilizers, lawn that gets frequently watered and mowed – can be considered a carbon sink. We are a society that excels at failing to grasp the big picture. The only way to believe Scotts’ claim that lawn is “a good foot soldier in the fight against climate change,” is if we ignore the entire carbon-spewing lawn-care process that the turf industry so avidly promotes.
On the bright side, we do have options for creating open spaces that actually are great carbon sinks: wildflower meadows; pocket prairies; clover lawns; “low-mow” grass mixes; lawns made up of native grasses, mosses and sedges; lawns full of violets, thyme, yarrow and dandelions; grass maintained organically and chemical-free; grass mowed with sheep; grass allowed to go dormant during dry periods. We can still have lawns…just not the kind that the turf industry has worked so long and hard to convince us to want. Now they’re trying to tell us that their style of lawn is good for the environment. Don’t believe it.
The alternatives to lawn are beautifully infinite…
… and infinitely beautiful.
© 2012, Sue Reed. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. If you are reading this at another site, please report that to us
About Sue Reed
Sue – you always say it best. Thanks very much for this thorough review. In my heart I knew lawn-as-carbon-sink didn’t make sense but it’s very useful to be able to articulate why.
Glad to do it. I just had to find out the truth for myself. (And maybe I’ll be able to use some of what I learned in the next edition of my book!)
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Sue – I rely on your careful analyses and look forward to every essay. Thanks so much.
Hi Nancy. I appreciate your support! And thanks for all the work you do with The Wild Ones.
Sue, excellent information! The statement by Scotts that they were good environmental stewards because lawns were good carbon sinks made very little sense to me. It’s just a ridiculous statement in general, but with your thorough research and listing of specifics helps us see just exactly how ludicrous this idea is. Thank you
Carole Sevilla Brown recently posted..A Love Letter to Wildlife
Fascinating stuff: facts, and how we interpret them.
Sue, love the depth of research. Next would be great to hear about warm/cooling factors of turf grass. I notice the temperature in the shade in my little woodland backyard is always cooler relative to shade under a neighbor’s tree that has only turf grass. Question is: Why?
Hi Julia, and thanks for your comments. Great observation! In fact, cooling the ground and the air are some of the big things I cover in my book, Energy-Wise Landscape Design. Maybe I should have included those considerations in my post, but blog-writing conventions seem to set limits on length.
Sue – terrific article and great in depth analysis. Thanks for walking us through those calculations. It’s always interesting to hear the other side to the various studies done by the industries selling products.
Keep it up.
Hal
Hal Mann recently posted..Goodbye Norway Maple
Thanks Hal. I look forward to reading your post about Norway maples…these are one of the few trees I don’t feel sad about having to cut down, when a project requires it. In fact, I have several colleagues who won’t even take on a project unless the homeowner agrees to remove the Norway maples altogether.
Verrrrry nice!
UrsulaV recently posted..The Container Of My Dreams
The roots of Kentucky Bluegrass grow as deep as the blades grow tall, which is only an inch or two. Not much mass to actually store carbon, Then look at the root systems of native grasses and forbs–the roots descend 2 to 15 FEET deep into the ground. Which os better at sinking carbon? No contest.
great point! thanks for bringing it up.
Thank you so much for this in-depth analysis of grass as a carbon sink. When I read that report by Dr. Ranajit Sahu, a month ago, I suspected a lot of poor and biased research, but did not bother to look into it further. So I am glad that you examined the matter so thoroughly.
It would be interesting to study an abandoned lot, gradually taken over by weeds. I bet that such neglected space would be a better carbon sink than the well kept, well watered, herbicide- pesticide-saturated lawn recommended by that study.
Beatriz Moisset recently posted..Inchworms: more little known pollinators
There are so many factors to consider in what makes a landscape good for the environment. Besides hating the idea of sterile lawn and all that’s involved in creating such an out-dated status symbol, I also object to Scotts oversimplifying the equation, all to make themselves look good and increase sales. The public may be too busy to pay attention, or too accustomed to just doing what’s familiar, but ultimately Americans are not dumb enough to believe for long the turf industry’s load of (toxic) bull.
Wow! Ditto to what everyone has said here. What an outstanding article and report on this subject of the bogus assertions from the lawn chemical industry. You took them apart, piece by piece in a very scientific and careful way.
May I reprint your article Sue on my blog?
Great work!!
Janet
Janet Way recently posted..Trees Are Fundamental to Shoreline’s Character
Janet, thanks so much for your support and your interest in reprinting articles by our team members. The best way to do this is to excerpt a small portion, like a paragraph or so, and link here to the original article, making sure to credit Sue Reed as the author. Thanks again!
Carole Sevilla Brown recently posted..A Love Letter to Wildlife
Hi Sue,
Great article and I generally support your conclusions with the exception of one. Natural ecosystems, forests, old fields, all living plant systems do emit carbon. Plants photosynthesize during the day and respirate at night. Like humans they take in oxygen and give off CO2 during this respiration period. It’s not that much and far outweighed by carbon sequestering during the day, but they do emit carbon.
This should not change our overall opinion as to the value of lawns (god I have to get rid of mine). They are, generally speaking, not ecologically friendly.
I love this website!
Bill
WildBill recently posted..Bottle of Summer
Hey there Bill, and thanks for the clarification about plants emitting some CO2 out at night. Y’know, even as I wrote that sentence, I felt a little twinge of wondering whether it was completely and totally true, but I ignored the twinge. (I should know better!) Some part of me must have been remembering that fact that I once knew, about respiration. I’ll see if I can correct that bit of the post. Glad you’re enjoying our team effort!
Sue, Thanks for doing all the research and crunching the #s for the rest of us. As many others have noted, the assertion that lawns are good carbon sinks just didn’t make sense so it’s nice to be able to have a strong, facts-based response once it comes up again…because you just know it will.
Debbie recently posted..Just Say NO ~ 5 Ways To Break Up With Your Lawn
Yeh, the lawn business is just too huge, and too vulnerable right now, as more and more people see through their falsehoods, to give up on this new treasure they think they’ve found.
I am president of the local Audubon and we have been promoting more native plants and less lawns to help reduce the continuing loss of our neotropical migrating birds. This great analysis added to my arguments against lawns, Thank you. By the way, I just finished removing 90% of my front lawn, getting ready to put in native grasses (no mowing, no chemicals, some water in the beginning) and some native flowers.
Your essay is much appreciated.
Charley
Sue, great article! As others have noted, it is very useful information. Now I need you to write one on why lawn isn’t all that great at stormwater infiltration. I am always trying to get developers to plant rain gardens or trees instead of grass!
Hi Kathy. Thanks for commenting, and thanks for all the noble work you do, trying to shift developers’ mentality. If you’re looking for good info about stormwater management, you might want to get in touch with Tina Schneider, who is one of us ex-Cons. She teaches at the George Washington University Sustainable Landscapes Program where I have done studio time on the subject of saving energy in our landscapes. This program is run/guided/overseen (not sure which) by Lauren Wheeler (another ex-con… we’re EVVerywhere!).
Thanks for the info, Sue!
Thanks Charley. Glad to be of assistance. If you want help your members find a lot more info about creating landscapes that actually are beneficial to the planet, you might recommend that they read Ellen Walther Sousa’s new book, The Green Garden, Catherine Zimmerman’s Urban and Suburban Meadows, or my (award-winning) book, Energy-Wise Landscape Design. Good luck with your new “lawn!”
A most excellent post! This will be a great resource when talking about lawns and the benefits of reducing them.
Ellen Honeycutt recently posted..Arbor Day in Georgia
Thanks Ellen. In this post I focused only on the carbon issue, because my goals was to clearly debunk the turf industry’s claims. But there are so many other great benefits to landscaping with less or no lawn, as you probably know. If you’re not already tuned into Paul Tukey’s group Safelawn.org, you might really enjoy checking out the info available there about the impact of lawn chemicals on people, wildlife and the world. Plus my book, Energy-Wise Landscape Design, presents hundreds of other ways to reduce the carbon footprint of our gardens and grounds.
It’s great that you gathered alllll the factors that go into carbon footprints of your basic lawn. Certainly those companies that stand to benefit are going to skew things by leaving out important factors.
Great Article Sue!
Loret T. Setters recently posted..Boys will be boys
Fabulous article Sue!!! Sadly the overworked and underpaid public is not paying attention in most cases . . . a voice like yours breaks through all the misinformation and downright lies out there misleading everyone. Thank you for your efforts here in so brilliantly documenting the truth.
Carol Duke recently posted..Flower Hill Farm BUTTERFLIES OF 2011 ~ Favorite Fritillaries Part Two ~ Surprise Ending!