As summer winds down, many of us can look back at fond memories in our backyards or in the yards of our friends or family. You may have attended a BBQ or pool party. Your kids may have ran through the sprinklers in your front yard or tossed a frisbee for the dog on your lawn. All carefree summer fun, right? Maybe not. Does a green lawn equal a green choice for the environment?
What’s Wrong with Lawns?
You may have guessed that given how many resources people pour into their lawns to keep them green, they aren’t actually that green in practice. In order to keep lawns green, lots of water is used. Many lawn owners also use harmful pesticides and herbicides on their grass. These toxins can end up in our waterways and in our food. And lawn maintenance releases greenhouse gases, such as with the fuel needed for lawnmowers.
Study on the Effects of Turf Fertilizer
A new study on the effects of turf lawns by the University of California, Irvine was recently released in Geophysical Research Letters. The study looked at the impact of fertilizer used to keep lawn grass green and lush.
Researchers looked at ornamental and athletic fields at four California parks and measured how much carbon dioxide was sequestered, how much nitrous oxide was released through fertilization and how much carbon dioxide was released through maintenance. They found that ornamental lawns, such as picnic areas, release a large quantity of harmful nitrous oxide. However, those emissions were offset by the carbon dioxide taken in by plants. However, athletic fields don’t take in as much carbon and often require more carbon emitting maintenance. The study found these lawns to be much more harmful to the environment.
Study on the Effects of Watering Lawns
Another study on the effects of lawns was conducted by Cristina Milesi and her team at the NASA Ames Research Center in California. Milesi’s study looked at the effects of lawns across America. She noticed that most of the grass lawns in the United States are not native to their area. The ecological impact of a lawn grows tremendously when the grass has to be imported and sustained in an unnatural environment.
Milesi explains, “A lawn isn’t a big deal in the northeast, but when you recreate that same landscape out West, it becomes a major ecological issue because the only way to grow those grasses is with high use of water and nitrogen fertilizer. An individual, quarter-acre lawn isn’t a big ecological influence, but adding up all those quarter-acres for everyone in the country . . . We suspected that the ecological impact could be pretty big.”
For the first part of the study, Milesi used a computer simulation to test the impact of watering your lawn based on a fixed amount or watering your lawn based on weather and evaporation rates. The reason Milesi looked at the amount of water used for lawn irrigation is because decreasing water tables and increased water waste is a large issue in America and around the world.
Milesi explained her findings saying, “If people watered according to what the meteorology indicated, factoring in temperature and humidity, for example, then it would improve irrigation efficiency—use less water—in the Southeast, where humidity is high. But in the West, there is so much sun and humidity is so low that plants can evaporate a lot more than 1 inch of water a week.”
With her simulation’s findings, Milesi was able to figure out how much water the US would need to keep lawns looking good. She estimated that 200 gallons of fresh water, suitable for drinking, per person per day would be required to upkeep lawns. That’s equivalent to about 400 water bottles per person per day just for lawns.
Study on the Effects of Carbon
The next part of Milesi’s study looked at the carbon emissions and carbon intake of lawns. She did this by simulating different amounts of fertilizer, watering schedules and whether cut grass was left or removed from the lawn.
Milesi made a strange discovery. She found that a well-watered and fertilized lawn could actually be a carbon sink - the lawn could take in and store carbon that would otherwise be polluting the air. The study revealed that if people left their grass clippings on their lawn to decompose, lawns across the US could store 16.7 teragrams, or 37 billion pounds, of carbon every year. If clippings are composted offsite, a smaller but still beneficial 5.9 teragrams of carbon would be stored each year.
Milesi explains the added benefits of recycling the clippings, “In fact, the model suggests that if we recycle the clippings on the grass, we can almost halve the amount of synthetic nitrogen fertilizer, and the carbon storage is still greater than it would be if we used the higher amounts of fertilizer but removed the clippings from the lawn.”
What are Alternatives to Lawns?
The studies above also published a number of alternatives to typical lawns we see in parks or our own backyards. One alternative, known as xeriscaping or xerogardening, is when lawns are replaced with native plants and mulch to limit the amount of water and maintenance needed in a garden. Grass lawns could also be replaced with clover, wildflowers or a meadow, all which require fewer resources to grow effectively.
In Milesi’s studies, she learned that the only places in the US where lawns were natural, not irrigated or fertilized, were small areas in the Northeast and the Great Plains. In areas where lawns are more wasteful than not, xeriscaping is encouraged. Xeriscaping also helps to conserve water - important in drought ridden areas. In bad drought areas, fines and other penalties are put into place for people who violate watering schedules and irrigate their lawns on their own time.