With the snow cover finally melting, we can see our yards again, and I’m sure many of us are thinking about gardening and lawn care. Since moving to Harvard and acquiring a lawn, I have begun reading up on what to do with the (in my case, not-so) green expanse.
According to a 2005 NASA-funded study using satellite imagery—the first, and still most widely cited such research—turfgrass lawn is the most extensive crop grown in the United States, outpacing even corn and covering about 40 million acres. Even though I’d rather not think about it, I am concerned with global warming: I know that how I maintain my small patch of America’s premier crop matters to the health of current and future generations.
Like many people, I absorbed ideas about lawn care from my parents. Although I bought a gas push mower (something I wouldn’t do again), I also have a predilection for keeping a natural lawn to attract insects, amphibians, and birds. Ironically, grass lawns tend to evoke a strong sense of home for many, despite the fact that they are composed of nonnative species and contribute to the demise of native birds and insects.
Recent research—including the Yard Futures Project, as well as a study of bees in suburban western Massachusetts published in Biological Conservation in 2018—affirms that management of yards can positively contribute to ecosystem diversity even as natural habitat shrinks. I am not suggesting we do away with the grass lawn, but rather that we recognize and mitigate some of the environmental problems associated with mainstream, suburban-type lawn maintenance. I want to share a little of my reading and research on this topic, so that this spring, we consider leaving some of the synthetic chemical fertilizer on the shelf at the local home supply store.
Synthetic, commercial fertilizers contain water-soluble nitrogen and some phosphorus, which washes into nearby bodies of water and groundwater. Massachusetts General Laws Part I. Ch. 128, §65A, however, considerably restricts the use of phosphorus in fertilizer to comply with federal law protecting waterways. Depending on the application, the weather, and soil health, a significant portion will wash away. Applying combined fertilizer and broad-leaf herbicide, known as “weed and feed,” is also concerning because the timing is off: It’s better to fertilize when grasses are growing, and de-weed later in the season. “Weed and feed” results in the over-application of herbicide, typically 2,4-D, which can harm nearby trees after just one application, according to the Wyoming State Forestry Division, and gets tracked into houses on the feet of pets and kids. It has been linked to negative health effects. Canada banned the use of weed and feed products in 2010.
Big picture effects
The water from your lawn flows into inland waterways, groundwater aquifers (affecting the quality of private well water), and, finally, out to the ocean. The EPA highlights nonpoint source pollution, to which fertilizers and pesticides from residential lawns are considered important contributors, as the largest and most difficult-to-address threat to U.S. waterways.
The Bare Hill Pond Watershed Management Committee noted in its last annual report (August 2020) that levels of phosphorus had increased in the deeper zone of the pond. Farther afield, WBUR reports regularly on pollution in the waterways and wetlands around Cape Cod, to which fertilizer runoff makes a strong contribution. Eutrophication, the depletion of oxygen in water generally from algae growth, is produced in inland waterways and coastal waters from the imbalance of nitrates and phosphorus. This kills aquatic life and is hard to remedy, especially as temperatures of coastal waters increase. Eutrophication of coastal waters isn’t just a regional issue but also generally affects U.S. coastlines—for example, every summer a massive dead zone forms, larger than the state of Connecticut, in the Gulf of Mexico, mainly from fertilizer runoff from the Midwest.
The use of synthetic chemical fertilizer also contributes to global warming. According to the Garden Club of America, homeowners use three million tons of fertilizer a year. For every ton of nitrogen produced for nitrogen-based fertilizer, representatives of the fertilizer industry in Europe (Fertilizer Europe) estimate that 2.5 to 4 tons of carbon are added to the atmosphere. Further, excess nitrogen not only washes off into waterways, but also, because it is water soluble, gets turned into gas and enters the atmosphere as nitrous oxide, a greenhouse gas that has much higher (up to 300 times) the heat-trapping potential as carbon dioxide. The EPA reported unprecedentedly high levels of nitrous oxide in 2015, due to agricultural usage.
Soil scientist Rick Haney travels around the country warning farmers that synthetic fertilizers deplete the soil by killing the good microorganisms that should be feeding their plants, and this will contribute to erosion, as well as poor crop yield (in the case of lawns, unattractive grass that then requires more fertilizer to look OK). Too much nitrogen on your lawn exacerbates soil compaction, making runoff worse, so over time, more fertilizer goes into the watershed. Excess nitrogen can also attract grubs, which in turn attract moles—and moles turn yards into a lumpy mess.
The more fertilizer a lawn receives, the more water it needs, because growth is stimulated and the grass takes up more water. Also, it requires more water input to look green. Therefore, fertilizer often goes hand-in-hand with the installation of automatic sprinkler irrigation. According to the EPA, landscape irrigation makes up about one-third of all residential water usage in the U.S.—equivalent to 9 billion gallons per day. Much of this water is wasted due to evaporation and runoff. Studies show that by 2050, about 50% of the world’s population will face water shortages: In the U.S., the West and Southwest are most vulnerable, but significant per capita decrease in water availability in Massachusetts has also been predicted starting in the next few decades.
The good news, I think, is that doing less is the best possible solution for most people! Mow less, let the grass grow higher. The grass will invest energy in growing good roots rather than stems and leaves. Good roots combat runoff and soil compaction and attract healthy nutrients back to the soil.
While I understand the attachment many people have to an emerald green lawn, there are nonsynthetic ways to make the lawn look great. Improving soil health with appropriate inputs of compost, allowing the grass clippings to stay on the lawn to cycle nutrients back into the soil, and letting fall leaves decompose back into the yard are great natural methods. (Oak leaves often take two years to compost, so homeowners may like to rake and compost them in piles before using them.)
One final, and very important, alternative is to plant appropriate native plants instead of those favored by the mainstream lawn industry. Kentucky bluegrass is not a native plant, despite its name: It was brought over as forage for livestock in the 19th century and outcompeted native grasses. This process can be witnessed in Midwestern prairies today, according to Global Rangelands (a collaboration of western land-grant universities), where Kentucky bluegrass is listed as an invasive plant in a number of states and outcompetes native prairie grasses. (Also, it seems to fare poorly in acidic soil, which is common around Harvard.)
Eco-friendly mixes of grass seed, generally a combination of tall and fine fescues, are available from a number of reputable suppliers, and require fewer inputs to grow nicely.
After all my reading and research, I’ve concluded that a green lawn does not equal a green Earth. We need to get used to the way grasses look when they are dormant, and think more about the health of the ground beneath our feet.
Catherine Warner of Harvard is an avid gardener, who during her undergraduate years in Virginia worked at local greenhouses and an organic farm.
For more information
- Rebecca Lindsey, “Looking for Lawns,” NASA Earth Observatory, Nov. 8, 2005, earthobservatory.nasa.gov/features/Lawn/lawn.php
- Susannah B. Lerman, Alexandra R. Contosta, Joan Milam, and Christofer Bang, “To Mow or to Mow Less: Lawn Mowing Frequency Affects Bee Abundance and Diversity in Suburban Lawns,” Biological Conservation, 2018, www.fs.fed.us/nrs/pubs/jrnl/2018/nrs_2018_Lerman_001.pdf
- Massachusetts Department of Environmental Protection, “Lawns and Landscapes in Your Watershed,” www.mass.gov/guides/lawns-and-landscapes-in-your-watershed
- Richard Shiffman, “Why It’s Time to Stop Punishing our Soils with Fertilizer,” Yale Environment 360, e360.yale.edu/features/why-its-time-to-stop-punishing-our-soils-with-fertilizers-and-chemicals