Lawns Reduce CO2 Levels

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Robert Pavlis

Is the lawn good or bad for the environment? You can look at this problem from different points of view and today I would like to examine the specific question; do lawns reduce CO2 levels.

A study done by Scotts  Miracle Gro concluded that “The lawn is a good and valued resource for sequestering carbon, even under various typical lawn management practices”. Is this really true??? The answer is more complicated than you might think.

Lawns reduce CO2 levels
Lawns reduce CO2 levels, source: Jeremy Page

 Carbon Sinking CO2

In our modernized society we produce too much CO2 (Carbon Dioxide) and if it is not causing global warming, the excess levels certainly don’t help the problem. One way to get rid of excess CO2 is to grow more plants. Plants take in CO2 and using photosynthesis they convert it to carbon and oxygen. The oxygen is released into the air and the carbon is used to build plant parts like wood, leaves, stems etc. A mature forest holds vast quantities of carbon.

It is ‘common knowledge’ that forests are great at removing excess CO2 – right? This is a myth–for details see my post Do Forests Remove CO2? But for now let’s assume that forests do remove CO2. Following this line of logic, it seems to make sense that a lawn would also remove CO2 from the air. Grass after all is a plant and as plants grow they do remove CO2 from the air.

Microbe Science for Gardeners Book, by Robert Pavlis

Is Grass a Carbon Sink?

Grass does remove CO2 from the air, but growing grass also produces CO2 – this is called a ‘carbon cost’. How much CO2 is being produced in growing and maintaining the grass?

Scientists have coined the terms ‘carbon sink’ and ‘carbon source’. A carbon sink is a system that stores more carbon than it produces. A carbon source is a system that produces more carbon than it stores (ex automobile). For the benefit of the environment we need more sinks and less sources.

What is the difference between CO2 and carbon? In environmental discussions the two terms seem to be interchangeable to some extent. It is CO2 in the atmosphere that is the problem for global warming. Plants convert CO2 to other forms of carbon such as wood. When plants die, the carbon in the plant will again be converted back to CO2. Oil is the result of dead plants – a form of carbon. When we use gasoline, which contains a lot of carbon, it gets converted to CO2. The conversion of carbon to CO2 and CO2 to carbon is a continual cycle.

Maintaining grass produces carbon (or CO2). Running the mower, watering the lawn, and even the fertilizer we apply all produce CO2. The mower burns gasoline and converts it directly to CO2. In order for you to have water, the municipality must pump it around, and filter it – this all requires energy and the production of energy produces CO2. Fertilizer needs to be mined, then processes and then delivered to your door. There are lots of engines burning fuel to make this happen.

The Scotts Miracle Gro article mentioned above and a report from Native Plant Wildlife Garden go through the calculations to determine how much CO2 is produced while maintaining grass and how much is absorbed by the grass. I won’t go into the details here. It is no surprise that the two sources of information disagree with the conclusion. The one group is promoting lawns and lawn care and the other is an environmental group opposed to lawns.

Does It Really Matter Who is Right?

I don’t think so. Let’s look at it in more practical terms.

There is absolutely no doubt that it is better for the environment to have natural grassland or a forest instead of a lawn. Any time we reduce the amount of gasoline we burn, or reduce the use of man-made products (water and fertilizer) we are doing good things for the environment. Is a lawn a good carbon sink compared to a forest or grassland – probably not.

People want lawns. No matter what the calculations say – we still want lawns.

The solution is fairly simple. Don’t make your lawn any bigger than you need. Have just enough to let the kids play a bit, and to make the house look good. If you don’t use the lawn, consider making it a natural wildlife place. If you have a larger lot, consider reducing the amount of lawn by converting some of it to a more natural environment. The lawn out front of your house is there for esthetics in most cases. This can easily be replaced with better options. Even maintained gardens are better for the environment than lawns.

Don’t Maintain Your Lawn.

You read right. Lawns don’t need much regular maintenance. Leave grass clippings on the lawn to fertilize it. Don’t buy extra fertilizer or at least reduce the amount you use – I don’t fertilize my lawn. Don’t water your lawn–most cold climate lawns naturally go brown in hot weather–accept this fact. It does need mowing from time to time, but it does not need it every few days. If you water less and fertilize less, you will mow less.

Allow moss and clover to grow in the lawn. You might even think of planting clover in the lawn.

Both sets of calculations in the above references assume a certain level of maintenance. If you reduce the maintenance, you will reduce your financial costs and you will reduce the amount of CO2 produced by your lawn.

Is a lawn a carbon sink? Is it good or bad for the environment? The answer depends on how you maintain it. If you follow my advice and reduce the maintenance, the lawn is probably a carbon sink and good for the environment. I don’t think it is as good as a natural forest, but we are human and want some lawn. Having grass is not our biggest environmental problem. Grass maintenance is a big problem.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

46 thoughts on “Lawns Reduce CO2 Levels”

  1. Most of the oxygen produced on the globe, and therefore sequestered carbon, is done by the oceans. That mechanism is much more efficient than a blade of grass or a tree. One of the reasons is that on land the exposure of the photosynthesizing surface has a lower maximum, i.e. a 4 inch blade of grass can’t sequester twice the carbon of a 2 inch blade of grass. A blade of grass returns its carbon much more quickly into the environment than a tree. Once the oceans rise, and the carbon sequestering increases, and the earth will start to cool and more poor people will freeze. The only way to prevent that environmental calamity is to keep mowing your lawn with that gas mower.

    I’ll explain the Ocean mechanism if anyone still reading this article is interested.

    Reply
  2. That’s a very interesting article. I found it because I was concerned that many people seem to be suddenly converting their gardens to having artificial lawns where I live. I’ve never watered my garden ever and I probably cut it less than ten times a year so hopefully I’m fairly good in that respect. My neighbour, who must have OCD or something, is obsessed with doing hers, sometimes twice a week. She loves spending money unnecessarily so maybe she’ll end up with a faux lawn. Make my life quieter at least!

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    • Not only do I believe that a lawn will sequester CO2, I believe that it will sequester CO2 quicker and in larger amounts if we set our lawn mowers to their highest cutting height- so that we keep our grass as long as possible. It would seem to me that a blade of grass that is 4 inches long will sequester CO2 twice as quickly as a blade of grass that is 2 inches long. That could double the sequestration rate.
      Dennis

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      • The important thing is the amount of carbon that is squestered – not the rate. A leaf of a certain size has the ability to squester more carbon, but it needs to do something with it. It can’t store an unlimited amount.

        Taller grass tends to have deeper and more extensive roots, which is where excess carbon is stored.

        Taller grass also shades the lower part of the leaf of its neighbors, which reduces photosynthesis in the lower portion of the stem and thereby reduces the rate of carbon sequestering.

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    • I agree as I don’t like to maintain my lawn. I know the making fertilizer creates CO2 and I don’t mind a brown lawn in the summer. It is natural and the more natural the better.

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  3. It’s great to see recognition of the lack of objective scientific data on carbon measurement: “It is no surprise that the two sources of information disagree with the conclusion. The one group is promoting lawns and lawn care and the other is an environmental group opposed to lawns.”

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  4. Seems to me we are not going to give up our lawns. That said, we can grow them: 1. without fertilizer and let them self fertilize by not
    collecting the cuttings,
    2. without weed killer, as mowed weed looks good
    enough,
    3. without watering, as the brown dormant grass
    comes back as rain returns and temperatures
    moderate,
    4. and make them as large a carbon sink as possible
    by setting our mowers to their tallest settings.

    If all of our lawns are catching twice or more the amount of carbon with 3 to 5 inch blades of grass rather one inch blades, then don’t we have a significant new way to combat environmental CO2? As a national or international movement, might this not be significant?

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    • I agree with your plan for maintaining lawns. Most of the arguments against lawns have to do with the way they are maintained. You are also right that we are not getting rid of lawns unless we find a practicable alternative. the call for everyone to turn their lawns into gardens will not work – most people do not garden.

      Longer grass does hold a bit more carbon, but real carbon sink is in the soil. It is the carbon that the grass adds underground that is important. Longer grass helps here to. But if you really want lawns to be good carbon sinks we need water them, and fertilize them so they grow well with large root systems. But then we are adding carbon in other ways like manufacturing and distributing fertilizer. There is no simple solution.

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      • If you can get over the ick factor, don’t mind going to all the extra work and aren’t bothered by the possibility the neighbors will think you’re a bit weird, you could fertilize your lawn with diluted urine. Urine is sterile unless you have a bladder infection and it contains a fair amount of urea, along with a little phosphate, potassium and trace amounts of magnesium, sulfate and calcium. It’s also more or less fossil-fuel free (depending on how the water you use to dilute it is pumped to you).

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  5. From what I’ve managed to find on the internets, lawns will reach their equilibrium state as a carbon reservoir when they reach ~35-50tC/ha. Once they reach that point, the amount of carbon flowing into them will be equal to the amount of carbon flowing back out of them.

    If you want to think about whether your lawn is helping combat the buildup of CO2 in the atmosphere, it’s probably best to think about it in terms of what you could call its carbon sequestration opportunity cost, which would be the difference between the lawn’s equilibrium carbon reservoir capacity and the capacity of the largest possible carbon reservoir that would realistically be there if the lawn didn’t exist.

    Absent human intervention, temperate forests would naturally return to most places where lawns and other turf grass expanses are currently maintained in North America and Western Europe. According to research from Oak Ridge National Laboratory, temperate forests reach their equilibrium state as a carbon reservoir at 325-371tC/ha ±30%. So if you live in the eastern half of the US or Canada, or in Western Europe, your lawn is preventing an additional 275-336tC/ha from being drawn out of the atmosphere and sequestered. If your lawn maintenance regime involves the use of fertilizers, burning fossil fuels or the application of materials whose manufacture and transport was fossil fuel powered, the carbon accounting of the lawn as a land management practice will be even worse, although it will not affect the lawn’s status as a modest carbon reservoir.

    http://www.esd.ornl.gov/projects/qen/carbon3.html

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  6. I am currently cutting my lawn at a much higher height than before to let the wild weeds flower. I can usually count twenty bees on my lawn at any given moment. I suspect doing this is a help to the environment and to the bees and other insects that are being threatened by pesticides etc. . I hope this helps the environment and hope others will consider raising the level of their lawn mower when mowing the lawn. How much this will help is not known to me, if anyone does know please comment..

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  7. I’m just trying to figure out whether or not I should be watering (occasionally). I use a reel mower, so other than the manufacturing waste from ten years ago (and the extra CO2 I expire while I do the work), I’m not too worried about my emissions. I have four trees on my 20′ x 125′ property, so I’m pretty sure I’m pulling my weight in terms of forestry. I don’t add fertilizer or soil. I do add grass seed in the Spring and early Fall, and I water daily while the sprouts are coming up. In the dry, hot summer, I generally let my grass go brown, but a lawn management guy on the radio the other day claimed that the CO2 sequestration from a healthy (not necessarily abundant) lawn would justify some minimal watering. I can’t find anything that backs that up or contests it.

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    • There are really two questions here.

      Is the amount of CO2 sequestered by grass more or less than the CO2 used to get water to the end of your hose? I don’t know the answer and it will depend on the CO2 required to get you the water – which changes for everyone depending on where they live.

      The second question is – is this good use of water. Water is a renewable resource. Any water we spread on the lawn will eventually end up back in lakes and oceans. The problem is that the water ends up somewhere else. If it is moved from a local river or aquifer to the oceans, then we won’t have enough fresh water. In many areas the levels of water are going down, and we need to start thinking of water as a non-renewable resource.

      I don’t think this is good use of water even if this use would sequester excess CO2.

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      • Agreed, and that’s why I haven’t been watering. I only looked this up because of someone (with a conflict of interest) on the radio telling me that it might be good for the environment if I did. I know that there are a dozen inputs to the equation, but it`s probably best to save the water for drinking.

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        • There is no problem with watering your lawn. Only 1 inch of watering weekly is necessary, the problem is over watering. There are many more wasteful sources of water usage than watering a lawn (which has many benefits), raising cattle for example, or producing a pair of jeans, fracking, etc. Concern for lawn watering is distracting us from industrial abuse of water usage, poor water infrastructure, and costs to move water around efficiently with a growing population. If you’re concerned about your own consumption, think about implementing a rain harvesting system at your home, even as little as a couple of rain barrels. Or further that by installing a gray water system. Concern for watering lawns in nonsense.

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          • I agree that over-watering is a problem – especially automated sprinklers that go on during a rain. I also agree that there are other bigger problems to solve, but for some areas like British Columbia and California – saving some water is important.

            I disagree with the statement “Only 1 inch of watering weekly is necessary”, at least for northern type grasses. They don’t need any water. I never water my lawn. If it does not rain, the lawn goes dormant.

            Your comment got me to ask – how mush water is it?

            Hope my math is right. There are 40.5 million acres of grass in the US. Assume these are all watered 1″ per week for 6 months. One acres = 4.35e4 sq ft. 1″ water = 0.083 ft. So 1 acre uses 3.6e3 cuft per week. Times 40.5 million acres, times 26 weeks = 3.8e12 cuft water = 2.8e13 US gallons (28,000,000,000,000).

            This is in the ballpark to the number reported by Scienceline: 2.6e12 cuft.

            Each person in the US uses 80-100 gal/day = about 32,000 gal/year (30% is for outdoor use).

            According to the above calculations, lawn watering in the US uses the same amount of water that 1 billion people use in a full year. The US has only 1/3 billion people, so there is clearly something not right with the above numbers. Assuming the number of acres of grass is right, then the only number that could be wrong is the 1″ per week. I suspect that a lot of the grass in the US in not watered.

            The 100 gal/day number and the 30% for outdoor use are based on a study – assume they are correct. If all of the outside use is for lawns, then 30 gal/day/person are used for lawns. That is 3.5e12 gal per year for the US. That is about 10% of the water used in the first calculation. That is still a lot of water but it seems to show most people do not water their lawns.

            Most people don’t have a gray water system, and don’t have the funds or desire to implement one. But everyone can stop watering their lawn.

          • I enjoy your contrary thoughts on the total CO2 controversy. I have been a landscaper planting trees, shrubs and grass for 30 years. I own a nursery where we grow some of the material we use as well as sell to others. I own some mature timberland as well. Your thoughts coincide with my own. Thanks for your honesty in the information you put forth.

  8. Interestingly, many of these practices don’t happen in my neighbourhood. The properties are small, so people use hand or electric mowers. For fertilizer, most people buy “triple mix”—soil, manure, and compost that comes from local garbage (I assume the manure is not a good things, but it has been produced in any case). We water our lawns, but not often because the climate is fairly rainy (this is late July and my sprinkler is on for the third time this season). We are not allowed to use poisons, so the grubs flourish, despite applications of beneficial nematodes that must alter the environment. Does that mean that we produce less carbon? or more?

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    • No idea if you produce more or less carbon. More or less than what? More than a weedy front lawn that you do nothing to maintain – yes you produce more carbon. Lots of driving around to get ingredients together to make triple mix and then deliver to you. Do you produce more than the person who is meticulous about their lawn and uses commercial fertilizer – probably not.

      Why use triple mix for your lawn? It does not need soil – it already has that. Manure and compost would be good additions, but you probably don’t need both.

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  9. Please explain how you say plants are better for the environment because lawns require water and fertiliser. Correct me if I’m wrong but plants too require water and fertiliser to thrive. You don’t have to use a chemical based fertiliser on your lawns as chook manure is an excellent natural form of fertiliser with very little chemical treatment. To say lawn mowers effect the environment is a little far fetched as I’m sure plant people also drive cars, use air conditioning and have other fuel driven appliances around the garden…even chain saws. Lawns naturally cool down your home and attract bird life and micro organisms in the soil which can only be good for nature.

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    • I don’t believe I say “plants are better for the environment because lawns require water and fertiliser.”??

      Gardeners with plants instead of grass do drive cars – so what – so do people with grass. I have large beds of plants – not native plants – and I don’t use power tools to maintain the gardens, nor do I use fertilizer. Most beds get very little if any water.

      If you grow a lawn, you do have to cut it – which uses fossil fuels.

      I doubt lawns cool your home any better than gardens, – if at all? – and they don’t attract as many birds as a garden.

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      • “If you grow a lawn, you do have to cut it – which uses fossil fuels.”

        Not if you use electric cutters that are powered by Wind generation. Also, being in the UK we need these lawn areas, or plant areas of some kind to absorb rain. We have to much at times.

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  10. It is difficult to deal with some kinds of myths because there is very little evidence one way or the other. The two studies you mention deal with carbon sequestration by lawns; but fail to compare it to the sequestration performed by trees. There are hardly any scientific publications making that comparison. Most studies simply concentrate on trees. The conclusion is that the trees with large, massive tree trunks are the best carbon sinks. The more biomass, the more carbon is stored. Lawns simply don’t have that amount of biomass.

    One of the few studies comparing lawns and trees was done by the University of Florida. Their conclusion was:

    . . . “highly maintained lawns and trees sequester much less CO2 than more natural areas with little maintenance. With more lawn cover than tree canopy cover, the balance can actually shift to emitting CO2”. . . http://edis.ifas.ufl.edu/pdffiles/UW/UW32400.pdf

    It is true that lawn will never go away entirely because humans like it. But your advice is very wise –reduce the size of the lawn, minimize the maintenance, plant trees. All this is good for the planet.

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    • My second reference compares grass to forests as carbon sinks. We don’t really need studies that compare the two. If one group measures grass and another forests, the numbers can be easily compared. I doubt anyone thinks that a tree contains less carbon than grass growing in the same area.

      Your referenced report is interesting, but I don’t agree with their main conclusion, namely that “highly maintained lawns and trees sequester much less CO2 than more natural areas with little maintenance”, implying that natural trees sequester more CO2 than planted trees. Their report only compares areas that have no grass to areas with both trees and grass. They then conclude that the latter areas sequester less CO2 – that is no surprise.

      I agree that there is very little good data. For example, I have found no good references that look at what happens under the ground with respect to CO2. I’ll discuss this issue and the idea of “more biomass = more stored carbon” in a future post.

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      • I have a suspicion, i.e. no proof:), that as the earth doesn’t care if we are here or not, in 1000 years the CO2 we have generated will be absorbed by the oceans. This especially as they expand with the ice caps melting. Now in the 70’s we were worried about the Ice Ages returning, Vis Nigel Caulders book at the time. By rights we should soon be under a mile or two of ice in the UK, no North sea, no Irish Sea – land bridges again.This was only 10,000 years ago!

        In turn, the oceans will absorb the CO2, along with all the plastic, it will be absorbed by living creatures who die, sink to the floor and get buried for millions of years. Then the new race that manages to arise will mine them for fuel. Perhaps a long view, or Deep Time, is the best way to look at things. Mind you the Sun will wipe everything out anyway if the Andomeda Galaxy impacting the Milky Way doesn’t do it first. Ah the mystery of life.

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