Americans are in love with – or, some might say, addicted to – their lawns. Green, manicured patches of grass are ubiquitous in most suburbs, where the majority of Americans live. At least 40 million acres in the United States, an area larger than the state of Georgia, are grass coveredthe standard lawn plant.
But what if growing and grooming this weed contributed to the planet’s biggest environmental crises, including water pollution and climate change?
That’s the view of a number of scientists who are increasingly talking about the downsides of lawns and the need to switch to alternatives – or, at the very least, more sustainable ways to manage your lawn.
“There are four things every parcel of land must do if we are to achieve ecological sustainability: sequester carbon, support pollinators, support a food web. And the other is to manage the watershed. A lawn is the worst choice out of those four ecological goals,” Douglas Tallamy, professor of agriculture and natural resources at the University of Delaware, told Yahoo News.
For climate change, the biggest issue is not what a lawn does, but what it doesn’t do. Every plant stores carbon dioxide, the most common heat-trapping gas that causes global warming. The more carbon stored, the better for the environment. But not all plants store the same amount of carbon. Generally speaking, the amount of carbon sequestered correlates with the size of a plant and its root system. This is why the logging of old trees, which tend to be taller than younger trees, is particularly harmful for climate change.
Compared to other plants that might grow in a yard, such as bushes and trees, grass has a very shallow root system. Much less grass grows above ground, especially if you cut your grass weekly to keep it neat and short. “In terms of carbon sequestration, lawns fail,” said Tallamy, author of “Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard.”
Then there’s lawn care and the machines that many Americans use to mow and clean their lawns: lawn mowers and gas-powered leaf blowers. According to the Environmental Protection Agency, gas-powered lawn mowers use 800 million gallons of gasoline – and spill another 17 million gallons of oil — every year. Two-stroke engines used by lawn mowers and leaf blowers are especially dirty because they don’t burn about 30% fuel they use, which releases volatile organic compounds.
A 2014 study found an idling scooter with a two-stroke engine releases 124 times more volatile organic compounds like an idling car or truck. The EPA says that operating a typical gas-powered lawn mower produces as many volatile organic compounds and nitrogen oxide – a potent greenhouse gas – as driving 11 new cars on average on the same period. In total, according to the agency, lawnmowers represent 5% of American air pollution (excluding climate). On top of that, many lawns are cut by a regular gardener, burning gasoline back and forth.
“Lawns depend on fossil fuels, period,” Douglas Kent, a landscape contractor who teaches at Cal Poly Pomona, told Yahoo News. “They don’t have to be, it’s just how we maintain them – mowers, blowers, edgers.”
Then there are the emissions associated with the manufacture of fertilizers. The most important ingredient in fertilizers is usually ammonia, which contains nitrogen that helps plants grow. Ammonia is produced at high pressure and high temperature. It therefore requires a lot of energy, which is usually provided by fossil fuels like coal and natural gas. The manufacture of ammonia is responsible for more than 1% global greenhouse gas emissions.
“[Lawns] are huge nitrogen consumers, and nitrogen is the most energy nutrient we make,” Kent said.
“When you add all of this energy that we dump into lawns and compare it to the amount of biomass stored in soil and tissue, you get 1 acre of lawn. [that] contributes about 3,112 pounds of carbon dioxide per year, which is the energy equivalent of 156 gallons of gasoline,” Kent added. (He made this calculation, drawing on previous research for data entries, for his book, “A New Era of Gardening: A Book on Gardening for Oxygen and a Healthier Atmosphere.”)
Many of the same attributes that make most well-kept American lawns a net contributor to climate change also cause them to fail Tallamy’s other sustainability tests. Fertilizer, for example, is usually mixed with an herbicide to kill weeds – the two-in-one products are called “weed and feed”.
But a person’s grass is an insect’s food. Weeds that pollinators depend on, such as clovers and dandelions, are routinely removed from lawns every day. And pollination is the very basis of biodiversity.
“Most vertebrates don’t eat plants directly: they eat things that eat plants, mostly insects,” Tallamy observed.
Similarly, short, regularly cut grass does not absorb much water – an increasingly important task as climate change brings more floods stronger storms – and that runoff can funnel fertilizers and herbicides into lakes, rivers and oceans, potentially poisoning fish and harming swimmers.
“Lawns destroy our watersheds, because, first of all, they don’t hold the water that other plants do,” Tallamy said. “It’s almost like paving the ground in a hot, dry summer.”
Grass is the most common irrigated crop in the United States, and lawns use 3 trillion gallons of water per year. Due to warmer temperatures and more severe droughts associated with climate change, water scarcity has become a crisis across much of the West, forcing local governments to limit the amount of water residents can use. outdoors, although many owners would be expected ignoring the rules.
Of course, lawns aren’t the only detrimental features of the yard. A concrete patio, which comes with its own carbon emissions from concrete production, has no ecological benefit.
So tearing up a lawn and covering it would not be helpful. But what to replace it with? Most experts simply suggest reducing the amount of space dedicated to grass and replacing some taller plants that will absorb more carbon and water. A tree that provides shade also reduces the amount of water that evaporates from the remaining lawn, which means it should require less water.
Ideally, some scientists say, only people living in regions that are moist enough to grow grass without additional watering would have lawns, and people in drier regions would plant less thirsty native species, like cacti in the desert.
There are also low-impact ways to maintain a lawn. Using only hand tools, such as a push mower or power tools, will eliminate emissions from two-stroke engines. According to the Electric Power Research Institute, replacing half of gas-powered mowers in the United States with electric mowers save so much emissions like taking 2 million cars off the road. Taking a more natural approach to lawn management — mowing it less often, skipping weed killer, and letting clovers and dandelions grow — would also minimize the impact.
Some state and local governments are beginning to take action on the worst environmental drawbacks of lawns. Responding to complaints about noise from gas mowers and leaf blowers as much as emissions, California Governor Gavin Newsom signed a bill last October that will phase them out in the state.
“Right now we’re using [lawn] as the default landscape: we put a few plants in our garden and everything else becomes lawn,” Tallamy said. “I want to reverse this. I want to have lots of plants and what’s left becomes lawn.