Americans love their lawns — a little too much, perhaps. And like all loves, this one has its chemistry — in this case, rooted in nitrogen, phosphorus and potassium, the key components of lawn fertilizer. Sure, it makes the grass grow. But that's not where the effects end if people over-fertilize or fertilize carelessly, and these nutrients end up getting into our lakes, rivers or water supplies.
According to the U.S. EPA's New England Regional Laboratory, 40 to 60 percent of the nitrogen that people put on their lawns through fertilizer winds up in "surface and groundwater."
While the eutrophication problem arises from many sources — much of it can be traced to agriculture and wastewater treatment plants — another key contributor is the large number of Americans busily tending to some 37.5 million acres of turf-grass covered residential lawns, and sometimes making mistakes that can really add up.
For some reason, these Americans feel that their lawns have to look a certain way — super green, with turf grass standing tall, as opposed to an alternative, less environmentally impactful lawn approach — and that fertilizer is the way to get that to happen. So what underlies the belief?
The short answer seems to be: our neighbors. A growing amount of research suggests that people fertilize and over-fertilize their lawns in significant part out of a sense of what those who live around them expect their lawns to look like.
In a paper published in 2012, Amanda Carrico of Vanderbilt and two colleagues found "strong social pressures surrounding lawn maintenance" in the Nashville area. Some 48 percent of people told the researchers that they used fertilizer on their lawns, and the study found that social pressures were a leading key predictor of their use of fertilizer.
A recent paper has found much the same result. The study, published in the February 2015 issue of Environment & Behavior by four University of Minnesota researchers, looked at two Twin Cities neighborhoods, and once again found that people's beliefs about what their neighbors think had a major effect on their fertilization behaviors. More specifically, in a sample of 942 homes, the research found that among those who perceived that their neighbors thought they should fertilize, there was an 85 percent chance of their actually doing so. In contrast, among those who perceived their neighbors felt they should not fertilize, there was a much lower chance (52 percent) of engaging in the practice.
"Neighbors are talking to other neighbors about lawns, and what they say matters," says the University of Minnesota's Kristen Nelson, one of the study's authors.
The study also looked at a particular group of individuals dubbed "high fertilizers" — those who said they apply fertilizer to their lawns four or more times per year. High fertilizers tended to live in suburbs, rather than in urban homes. They tended to employ lawn services rather than managing lawns themselves. But surprisingly, in this group — a smaller number of individuals — the role of neighbors was actually slightly the opposite from what was expected, predicting a slightly decreased (rather than increased) likelihood of being a high fertilizer.
That may just be a quirk of the study, notes lead author Nicholas Martini of the University of Minnesota. "We have less confidence in the result because the statistical significance is weaker and the overall effect is small," he explained by e-mail.
As winter fades and lawns start to recover, fertilizer season is about to begin. The latest research suggests that as the grass starts to regrow, people won't only be eyeing their own lawns for green shoots — they'll be eyeing those of their neighbors, as well.