The Science Against No Mow May

Other lawn practices may be more beneficial to pollinators, including a potential "sweet spot" for mowing frequency.

Gaining in popularity, “No Mow May” is increasingly being practiced by well-meaning property owners as a means of feeding early Spring pollinators. It seems a sound, simple concept: allow grass to grow for one month and more flowers bloom, providing food for bees and others. Yet a 2018 mowing study, as well as some expert opinions, suggest it may not be the most beneficial practice and there’s actually a surprising potential “sweet spot” for mowing frequency to support pollinators.

A Study Retracted

First popularized by UK-based Plantlife, No Mow May was championed stateside by Bee City USA, a Xerces Society, as well as the city of Appleton, WI. It has since been written about in the NY Times and many other publications, spreading the grassroots initiative.

Yet according to the director of state and local government relations for the National Association of Landscape Professionals (NALP), Bob Mann, the research Appleton relied upon—conducted by a city resident who is also a university professor—has since been retracted. This was due to “finding inconsistencies between the published summary data and raw data.”

Mann looked into No Mow May and reported the news this past Tuesday on the NALP site in “The Truth About ‘No Mow May’.” He writes, “News stories in early April 2023 out of Appleton suggest that in light of the study retraction that the city is considering abandoning their ‘No Mow May’ policy.”

A Mowing Frequency “Sweet Spot?”

When Turf covered the issue last year, we reported how the initial No Mow May in Madison, WI, located about 100 miles south of Appleton evolved into a “Low Mow May.” According to NBC15, “City leaders put their own twist on the ‘No Mow May’ movement cutting its way across Wisconsin by passing what they call ‘Low Mow May.’ So, while homeowners cannot simply lock up their lawnmowers until June, they will only be required to mow once during May, rather than every seven to ten days, and be allowed to raise the mower height to four inches, rather than the two to three inches more commonly used.”

While the measure was no doubt meant as a compromise between supporting pollinators and city maintenance codes, such solutions may actually represent an ideal for all involved. In his article, Mann cites findings of another study that determined a potential mowing frequency “sweet” spot for supporting pollinators. They found:

  • Lawns mowed weekly remove weed flowers so there weren’t very many pollinators.
  • Lawns mowed every two weeks had far more pollinators visiting.
  • Lawns mowed every third week showed less pollinators than lawns mowed every two weeks.

According to Mann, “The researchers theorized that the reason why there were more pollinators in the two-week lawns versus the three-week lawns was that it was easier for the pollinators to access the flowers in the two-week lawns.”

This idea is backed up by Katerina Jordan with the Guelph Turfgrass Institute at the University of Guelph. In an April 28 interview with CTV News Kitchener she said with unchecked grass growth, “what’s going to end up happening is you’re going to have competition and overcrowding and self-shading. Self-shading is when you have plants within a community that shade each other.”

Other Ideas

Jordan’s colleagues, Dr. Eric Lyons, a professor in University of Geulph’s Department of Plant Agriculture and the director of the Guelph Turfgrass Institute (GTI) and Dr. Sara Stricker, GTI’s communications and outreach coordinator and instructor for the Diploma in Turfgrass Management program at UG are also critical of No Mow May. The pair assert the initiative while “well intentioned…, is also misguided” in “‘No Mow May’ Bad Idea for Canadian Lawns, Say U of G Turfgrass Experts” posted on April 24.

No Mow May
Dr. Eric Lyons

They say many early-flowering weeds that can be found in lawns, such as dandelions, are actually an incomplete source of nutrition for pollinators. “Dandelions aren’t going to save the bees,” says Lyons. “A much better nutrition source for them are flowering trees, like crabapple, choke cherry and even maple, oak and willow.”

You can still enhance the pollination possibilities in a lawn, however. “You can mix in low mow flowers. Clover is a perfect example. So there is no problem with having a grass and clover mix. And the beauty of clovers is you can mow it. So again, no reason to just leave it be for an entire month,” Jordan told CTV News.

No Mow May
Ajuga reptans in my front lawn.

Editor’s Note: In an area of my lawn where the grass struggles, I planted plugs of ajuga reptans, a pollinator-friendly plant commonly known as bugleweed. It’s low growing, spreads, evergreen, and blooms at the same time as dandelions. However, it is listed as an invasive and some say it can outcompete the grass. Thus far, over several years, mine has been behaved and creates gorgeous blankets of purple in the Spring. The “chocolate chip” variety is supposed to be slower growing.

UG experts also point out that creating temporary habitats in the form of an overly long lawn is not helpful to pollinators if the plan is to eventually mow the grass into a lawn. A better idea is to create wildflower zones in home gardens with pollinator-friendly grasses and shrubs to benefit insects and wildlife all year round.

Dr. Sara Stricker

From a turfgrass perspective, “No Mow May” can harm the lawn. “Allowing lawns to grow long can encourage the growth of undesirable weed species such as thistles, prostrate knotweed and wild violet, which are difficult to remove once they become established,” said Stricker.

After No Mow May, cutting too much of a grass’s length at once in June is also traumatic, leaving the grass with a sudden loss of an energy source during an active growing time. It can increase the risk of “scalping” the turf, making the lawn more susceptible to insects, weeds and disease.

“We recommend mowing home lawns when the grass reaches approximately three inches high,” said Lyons. “Grasses have evolved to be grazed upon by herbivores, so they actually respond positively to mowing practices.”

To summarize, here are other lawn strategies to try for benefitting pollinators:

  • Mow every two weeks in May.
  • Incorporate clover and other low-growing flowers in turfgrass.
  • Create a wildflower zone on your property.

For more information, read “Could Your Landscape Business Handle A No Mow May?”

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