Criticism

Not everyone was quick to accept the results of the Del Toro and Ribbons study. In a blog post titled “Documenting serious issues in a bee paper on ‘No Mow May,’” University of Minnesota bee taxonomist Zachary Portman wrote that the paper “had such serious issues that I [Portman] took the step of alerting the journal” (Portman 2022). Portman summarized his concerns into two main categories:

1. “The paper reports multiple bee species that simply do not occur in Wisconsin in May.”
2. “The paper methods state that the majority of specimens were identified by sight in the field. This is a problem because many of the listed species require a microscope to identify.”

Additionally, Dr. Portman called attention to the fact that the study referenced plants unlikely to bloom in the study area in May, misspelled numerous species names, and cited inadequate sources such as regional checklists as their bee identification resources.

Twenty-six months after alerting PeerJ of his concerns, the Del Toro and Ribbons study abruptly fell from grace. On November 18, 2022, the journal retracted the study stating that they found “several potential inconsistencies in data handling and reporting.” Following their retraction, The New York Times redacted their story on Now Mow May to exclude the retracted study (Readel 2022b), and Bee City USA removed references to it on their website (Bee City USA 2021b).

Citing the lack of scientific evidence, in March 2023, Appleton Alder Chad Doran filed a resolution to “eliminate the No Mow May program,” which he described as “divisive” (Charniak 2023) “and delete references to it from the city code” (Appleton 2023). Ultimately, the resolution didn’t pass the council committee and drew ire from the authors of the retracted paper, with Ribbons calling it “a form of bullying,” Del Toro accusing Doran of trying to “just bring attention to himself,” and stating that the results of a new study will soon be published (Behnke 2023).

Analysis

Does No Mow May live up to the hype? Given its increasing media attention and viral spread, coupled with a relative absence of critical analysis, the need to objectively weigh the benefits and drawbacks of the movement became increasingly apparent. In doing so, we factored in the scientific/ecological, and cultural aspects. Not part of No Mow May’s claim, but sometimes included in its defense, we found the potential human health implications relevant to our analysis.

Scientific and Ecological Considerations

• Lack of supporting empirical data — Following Peerj’s retraction of the Del Toro and Ribbons paper, the ecological impact of Now Mow May is currently unsupported by any peer-reviewed research. Conversely, another often-cited study on the relationship between bee species and abundance to lawn mowing frequency effectively contradicts the claim that extended periods of non-mowing equate to more bees (Lerman et al. 2018).
• Food for Pollinators — Yes, cessation of mowing will allow some nectar-producing plants to flower, thus providing food resources for pollinators. However, since most of the biomass of a typical urban/suburban lawn consists of primarily wind-pollinated plants (literally all grasses, plus plantains), unmowed turf makes very inefficient nectar and pollen habitats. Additionally, at least one study has concluded that dandelion (Taraxacum officinale) pollen is of relatively low nutritional quality to honeybees (Apis mellifera)(Loper & Cohen 1987).

• Temporary Habitat — Pollinating insects and other animals are unaware of the difference between temporary and permanent habitats. Therefore, fauna using unmowed lawns, such as ground-nesting bees, nesting eastern cottontails, snakes, mice, voles, and fledgling birds seeking shelter, could be in for a lethal surprise when mowing resumes in June.
• Ecologically Questionable Plants — Not all plants likely to pop up in an unmowed lawn are innocuous, nor should they be encouraged. The Del Toro/Ribbons study includes a table of the most common “flowering plants” from their survey. The list contains Creeping Charlie (Glechoma hederacea) and Canada thistle (Cirsium arvense). The former recognized as invasive by ten states and the latter by 39 (Invasive.org 2018a, Invasive.org 2018b). Furthermore, Bee City USA’s No Mow May FAQ page contains an image of what appears to be goutweed (Aegopodium podagraria), a plant also recognized as invasive by ten states (Invasive.org 2018c).
• Potential for Adverse Reaction — Not everyone will participate in No Mow May, and those who choose not to may not appreciate having their neighborhoods inundated with dandelion and other wind-spread lawn weed seeds. In her blog, Wisconsin’s Erin Schanen, “The Impatient Gardener,” contends that “homeowners who pride themselves on a perfect lawn will likely increase their herbicide applications to counteract a burgeoning dandelion population” (Schanen 2022).
• Reduced Emissions — On a more positive note, less frequent mowing means lowered carbon emissions from mowers still containing internal combustion engines.

Cultural Impact

• Aesthetically Unappealing — Let’s face it, if No Mow May was attractive, people wouldn’t need signs to explain it to their neighbors. In fact, according to the New York Times, in the case of Allison Roberts of Prairie du Chien, Wisconsin, the appearance of her lawn was so alarming that she was awoken from her nap by police officers pounding on her door to ensure that she was still alive (Readel 2022a). The Times continued that one of Robert’s neighbors eventually got fed up and mowed her lawn without her permission.

• Misleading Marketing Materials — Almost universally, the Now Mow May yards signs depict unrealistic, botanically inaccurate, cartoonized floral meadows rich with biodiversity and color. Some, such as the signs produced by Greenbelt, Maryland, feature flowers that occur much later in the year (Harris 2022), and almost none of them include the non-showy, wind-pollinated plants that comprise the majority of typical American lawns.
• June Complications — According to Texas A&M, Kentucky bluegrass (Poa pratensis), perhaps the most abundant turf grass in the midwestern United States, grows 18–24 inches high (Duble 2023). Numerous sources state that no more than one-third of turf grass should be cut at one time (Bauer and Reyes 2018, Duble 2023). According to the University of California, removing more than one-third of the blades damages the root system, slows growth, and increases the susceptibility to weeds, disease, and thatch build-up (UCANR 2017). Therefore, if your grass has achieved a height of 15 inches by June 1, the first mowing should be no shorter than 10 inches, which will require alternative means of cutting as a 10-inch height setting is beyond the capacity of most residential mowers. Following the recommended regimen of removing no more than one-third of the blade with each cutting would likely result in three to four mowings over several weeks to return to pre-May height.
• Pollinator Advocacy — Despite having numerous issues, No Mow May has increased public awareness of pollinator decline while drawing attention to the fact that monocultures of turf grass are not ecologically sustainable environments.

Human Health Factors

• Ticks — Does the cessation of mowing cause an increase in the abundance of ticks? There doesn’t appear to be a clear-cut answer. The most widely referenced study, conducted on 16 suburban properties in Springfield, Massachusets, found no increase in ticks between lawns mowed every week, two weeks, and three weeks (Lerman and D’Amico 2019). Aside from being geographically limited, the study’s mowing cessation maximized at three weeks, less than the duration of No Mow May. In their No Mow May Impact Report, the city of Sun Prairie, Wisconsin, states there is currently no available data linking No Mow May to the abundance of ticks (Sun Prairie 2022). However, the Centers for Disease Control recommends frequent lawn mowing and clearing tall grasses as ways of “preventing ticks in the yard” (CDC 2019). To summarize, given the small sample size of the most recent study and the conflicting recommendations from the CDC, it seems reasonable to conclude that more research is needed.
• Allergens — The impact of Now Mow May on human allergies is also unresolved. Sun Prairie’s before-mentioned impact report also downplays the impact of No Mow May on allergies (Sun Prairie 2022). However, many of the plants affected by No Mow May are wind-pollinated and allergenic. The Asthma and Allergy Foundation of America lists several turf grasses, including Kentucky bluegrass (Poa pratensis), as common allergens and recommends keeping lawns short to prevent allergies (AAFA 2021). A fact sheet produced by Thermo Fisher Scientific states that “Kentucky bluegrass is severely allergenic” (Allergyinsider 2021), and a medically-review article published by WebMD lists “unmowed lawn” as a condition that makes grass allergies worse (WebMD 2022). A plausible reason for the lack of allergenic impact referenced by the Sun Prairie impact statement could be that Now Mow May is relatively new, and participation is still somewhat limited.

Discussion

Worldwide, insects are in steep decline, and it’s not just those who pollinate either. A 2019 paper published by the journal Biological Conservation looked at 73 historical reports of insect decline and concluded that up to 40% of the world’s insect species are at risk of extinction over the next few decades (Sánchez-Bayo and Wyckhuys 2019). The authors listed, by order of importance, the reasons for the decline:

1. Habitat loss due to agriculture and urbanization
2. Pollution, including pesticides and herbicides
3. Biological factors, including pathogens and introduced species
4. Climate change

For the most part, conservation-minded individuals agree on ways to reduce these factors related to insect decline. We understand the consequences of pesticides and herbicides. We take steps to reduce our carbon footprint and are careful not to help spread invasive species.

Regarding habitat, property owners can also make a difference in their communities. Scientists have well-documented the importance of native plants as food sources for native insects (Ehrlich and Raven 1964, Tallamy et al. 2020). They also recognize that some genre of plants are more productive than others at providing food and shelter and that lawn is not an ecologically-sustainable habitat (Hostetler and Main 2010, Hostetler and McIntyre 2001, Tallamy 2007).

Experts and conservation organizations recommend methods that improve wildlife friendliness in residential and commercial landscapes. The Natural Resources Defense Council (Talbot 2016), National Audubon Society (NAS 2016), and the website homegrownnationalpark.org (HNP 2023) are among those who recommend shrinking the size of lawn areas, adding native plants, and removing invasive species. The NRDC also cautions about the potential influx of invasive and undesirable species in no-mow areas and recommends frequent weeding. Additionally, the National Wildlife Federation maintains lists of keystone (most critical) native plant species by ecogregion (NWF 2023).

Conclusion

Although well-intended, given everything we currently know about No Mow May, particularly the lack of supporting science coupled with concerns over potentially detrimental environmental and cultural impacts, precludes us from endorsing the movement as scientifically factual or even good practice. Hypotheses such as those benefits claimed by supporters of No Mow May require much greater study than what has been conducted. Not only is further research necessary, but to be credible, this research must come from independent entities who lack professional conflicts of interest with the results.

Within human habitations, the long-term health of pollinators and other wildlife are better served by planned and maintained native plant gardens instead of unsightly, short-lived habitat dominated by exotic wind-pollinated plant species.

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