It’s summer in Minnesota.  The sun is shining, everything is a rich vibrant green, and the smell of fresh cut grass is wafting through the window.  That smell triggered childhood memories for me…as well as curiosity: what is the carbon footprint of lawn care?  Before we calculate our lawn's footprint, let's look at some lawn facts:

• 80% of all residences in the United States have private lawns.
• Lawns cover 31,629,440 acres in the United States.  This is an area equal to the New England states combined – making lawn the largest irrigated crop in the country.
• 54 million homeowners maintain lawns.
• The average lawn size is 6/10ths of an acre.
• 1 hour of gas powered lawn mower use produces 11 times the emissions of driving the average new car for an hour. 
• The average length of mowing season in the United States is around 32 weeks

1 hour of lawn mower use produces 11 times the emissions of driving the average new car for an hour.

An acre of grass, whether maintained or left alone to grow unmolested, will sequester approximately 3,600 pounds of greenhouse gas annually which seems pretty impressive.  Switch grass, however, will sequester up to 10,000 pounds and a stand of maple trees 13,740 .  Consequently, an argument could be made that part of the carbon footprint of our lawn is the difference between the amount of carbon native landscapes like switch grass or forest can sequester and the much smaller amount sequestered by man-made grass lawns.  We’ve decided not to include this number in the total calculation of a lawn’s carbon footprint, however, we believe it makes the case that a maintained lawn should not be considered carbon negative  .

The carbon footprint of lawn maintenance comes primarily from three inputs: mowing, lawn chemicals, and irrigation.   For lawn chemicals and irrigation this input is an embodied carbon footprint, meaning comes from the use of fossil fuels required to mine, manufacture, process, package, and distribute the resource to customers. For mowing, the carbon footprint is a direct input – meaning the use of fossil fuels to power the lawn mower.

Mowing:
Surprisingly, regardless of whether you use a “walk behind” or riding mower, if it is powered by gasoline it will consume roughly the same amount of fuel per mow: approximately 9/10ths of a gallon of gas for an average lawn, producing 17.6 pounds of greenhouse gas.  With an average mow season of 32 weeks, that is 563 pounds of CO2 annually.

Lawn Chemicals:
In a study by Christiine Milesi of NASA , the carbon emissions associated with residential lawn fertilizers averages 195 pounds of greenhouse gas per acre and a study by Zhang et al identified the footprint of pesticides at 104 pounds per acre.  This means for an average sized lawn, the chemicals used account for 179 pounds of CO2 annually.

Irrigation:
According to a detailed study by The River Network, every gallon of tap water is responsible for 0.14 ounces of CO2.  According to the EPA , the average American household uses 35,000 gallons of water for exterior irrigation annually for an irrigation carbon footprint of 306 pounds of CO2.

Adding Up Your Lawn’s Carbon Footprint:
As the numbers above add up, maintaining an average lawn of 6/10ths of an acre will be responsible for 1,048 pounds of CO2 annually.  Remembering that this represents man-made atmosphere, this is a volume of 9,327 cubic feet of greenhouse gas added to the atmosphere.  All told, then, the 54 million households maintaining lawns produce 503 billion cubic feet of atmospheric greenhouse gas annually.  And these emissions will remain active in our atmosphere for up to 200 years .

What You Can Do To Repair That Impact
We will be posting an entry in our Practically Green Sustainability tips to identify ways you can reduce your lawn’s carbon footprint.  You can also offset your lawn’s impact with a BLUEdot Easy Offset.

What ways have you found to reduce your lawn’s energy and water use?