Why you may not want to let your lawn grow wild this ‘No Mow May’
“No Mow May” started in the U.K. as a campaign to increase biodiversity. But new research reveals a month without mowing may not be as beneficial for lawns everywhere.
When spring rolls around in the northern hemisphere, so do conversations about “No Mow May.” Homeowners forego mowing, allowing otherwise hidden flowers to bloom in your lawn, increasing your yard’s biodiversity and providing food for pollinators like bees. However, scientists have increasing questioned whether this trend, which began in the United Kingdom, is compatible with United States lawns.
Many U.S. lawns are filled with non-native species like dandelions (Taraxacum officinale), which Europeans colonists introduced to North America. These plants are not necessarily a good food source for native pollinators as they lack certain important amino acids that make nectar and pollen nutritious.
Because of concerns like these, No Mow May has actually “become quite controversial” in the U.S., says Grace Glynn, the state botanist for the Vermont Fish & Wildlife Department. “I mean, who knew dandelions could be so controversial?”
Why did No Mow May begin?
“No Mow May” started in 2018 as a campaign by the U.K. organization Plantlife. The group originally coined the slogan to encourage local U.K. councils to manage green spaces more like traditional hay meadows to increase biodiversity, according to Sarah Shuttleworth, a specialist botanical advisor for Plantlife.
Historically, workers who tended hay meadows let them grow long throughout spring and most of the summer, only cutting them at the end of summer to make hay. Plantlife picked May as the month to focus on for two main reasons: May is the month that many U.K. grassland species start to flower (although climate change is shifting that), and May is also when farmers traditionally removed animals from hay meadows so they could grow. Plantlife suggested local authorities test out the hay meadow management style with “No Mow May.”
Plantlife soon realized that the slogan was catching on with the public, and that “this could be a really great way to engage the public about the importance of grasslands,” Shuttleworth says.
In the U.K., she says, “people’s lawns are often kind of relic grasslands,” and letting them grow can reveal native flowers they didn’t know they had in their lawn. These flowers provide nectar and pollen for native bees and other local pollinators that evolved alongside these plants.
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Plantlife chose May for its campaign because it aligns with traditional hay meadow management, not because there was specific scientific evidence about not mowing in May. Since the campaign started, there has been at least one study examining its effects: In 2022, Ecological Solutions and Evidence published a paper showing that un-mowed grassland plots in the U.K. produced more nectar in mid-late May than mowed plots, providing more food for native pollinators.
But in the United States, the effects of No Mow May aren’t necessarily the same.
Why No Mow May never took off in the U.S.
No Mow May caught on in the United States as early as 2020, when the city of Appleton, Wisconsin, started encouraging residents to participate.
In September of that same year, the journal PeerJ published a study purporting to show the benefits of Appleton’s No Mow May. Yet two years later, PeerJ retracted the paper, citing “several potential inconsistencies in data handling and reporting.”
By the time PeerJ retracted the paper, more than 30 U.S. cities had adopted No Mow May initiatives, and many individual households had become interested in practicing it. But at the same time, scientists began to question whether this was the right strategy for U.S. lawns.
The U.S. has more varied climates compared to the U.K., meaning that flowers bloom at different times across the country. In addition, the country’s history of colonization means that a lot of the plants in U.S. lawns (including, often, the grass itself) are non-native species, Glynn says. These non-native plants don’t necessarily provide good support to native pollinators.
In 2024, Appleton announced that it was dropping No Mow May in favor of “Slow Mow Summer.” The city now encourages residents to raise their lawnmower’s blades to four inches and wait to mow until the grass reaches six inches. Many other U.S. cities have moved away from No Mow May, too. Like Appleton, some have replaced the initiative with slogans like “Less Mow May” or “Slow Your Mow.”
The benefits of a Slow Mow Summer
Scientists suggest that mowing less frequently throughout the growing season and prioritizing the growth of native species could be a better strategy for U.S. lawns than practicing No Mow May.
Slower or less frequent mowing does have some scientific support in the U.S. In 2018, Biological Conservation published a study in which researchers mowed Massachusetts lawns at different intervals between May and September. They were surprised to find that lawns mowed every two weeks yielded more bees than lawns mowed every week or every three weeks. They theorized that this was because two weeks was long enough for flowers to sprout, but that at three weeks the grass length made it harder for bees to get to those flowers.
The study didn’t focus on which flowers bees targeted, but Susannah B. Lerman, a research ecologist for the U.S. Forest Service and co-author of the paper, says that out of the roughly 60 species of lawn flowers they identified, about a third were native and therefore supportive of local pollinators. Glynn says she sometimes mows around native plants in her lawn to encourage their growth, although this does require some extra research on the mower’s part to figure out which ones are native.
Doing what you can
There’s one key barrier to mowing less in the U.S. that doesn’t exist in the U.K.: local ordinances may fine homeowners if they let their lawn grow out too much. When the city of Appleton announced it would transition to Slow Mow Summer, it also noted that properties with weeds or grass over eight inches may receive fines.
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The financial burden of fines is also tied with the social burden in the U.S. to keep a trimmed lawn. Lerman and her colleagues did all the mowing for their study, and when they arrived at the houses that were due for a three-week cutting, she says “we could barely get out of the car and get the lawnmower out of the car before the householder ran down to meet us and was like, ‘I’m so glad you’re here, my neighbors are getting really upset about my lawn.’”
Although Lerman would advise U.S. homeowners to choose slow mowing over No Mow May for both ecological and social reasons, she thinks that “if that’s their gateway into thinking about other ways of managing their lawn, that’s fantastic.”
Glynn feels similarly, saying she thinks of No Mow May “as a gateway towards ecological gardening,” which involves cultivating native plants.
