Why 'Lazy' Lawn Mowers Are Heroes for Bees

There's no shame in an unmowed lawn. Not only can wild yards and gardens look better than commonly believed, but cutting back on cutting grass can save significant time, energy and money. According to a new study, it could even help save bees.

Led by ecologist Susannah Lerman at the University of Massachusetts Amherst and the U.S. Forest Service, the study examined how homeowners can boost bee habitat with their lawn-care habits. Mowing every other week seems to be the sweet spot.

"We found that backyards can be a surprisingly beneficial habitat for bees," Lerman says in a statement. "Mowing less frequently is practical, economical and a time-saving alternative to replacing lawns or even planting pollinator gardens."

Flower Power

Why would bees care how often we cut our grass? By mowing every two weeks instead of weekly, we allow more blooming of "weed" flowers like clover and dandelions, thus providing more foraging habitat for local bees. Habitat loss is an increasingly dire problem for many bees and other pollinators, whose ancestral wildflower meadows are increasingly replaced by human development.

Yet because grassy lawns are so widespread in many human-altered landscapes — with roughly 40 million acres across the U.S., for example — their collective influence on bee populations could be huge. That's why Lerman and her colleagues decided to investigate the effects of a "lazy lawn mower" approach, as they call it.

For their study, published in the journal Biological Conservation, the researchers recruited 16 homeowners with lawns in Springfield, Massachusetts. They divided the homeowners into three groups, then mowed their lawns at one of three frequencies — every week, every two weeks or every three weeks — for two summers.

Each lawn received five scientific surveys per season, starting with a property-wide count of "yard flowers" (ornamentals unaffected by mowing) and "lawn flowers" (plants like clover and dandelion growing within the grass). The researchers also recorded average grass height for each lawn, as well as bee abundance and biodiversity, to see how the insects responded to different mowing rates.

Lazy Like a Fox

More than 4,500 individual bees were observed during the study period, representing about 100 different species. This included a motley crew of native bees, the authors point out, from various bumblebees and carpenter bees to leafcutter, mason and sweat bees. The exotic European honeybee (Apis mellifera) made lots of appearances, too, but it was often outnumbered by native species.

Yards mowed every three weeks had up to 2.5 times more lawn flowers, the study found, and hosted a greater diversity of bee species. Yet the abundance of bees was highest in lawns mowed every two weeks, which supported 30 percent more bees than lawns mowed at one- or three-week intervals.

It makes sense that weekly mowing was associated with fewer bees, since it limits the availability of lawn flowers. But if a lawn mowed every three weeks has more flowers than a lawn mowed every two weeks, why wouldn't it also have more bees?

The study's authors aren't sure, but they have a theory. The taller grass in lawns mowed every three weeks, they write, "may have prohibited access to the flowers, rendering the floral-abundant lawns less attractive." In other words, lawns mowed every two weeks offered the bee-friendliest balance of grass height and flowers.

Bee the Change

It might seem trivial to study the landscaping preferences of bees, but only if you ignore the huge ecological and economic roles they play. Bees of all stripes are vital pollinators of wild plants and agricultural crops, enabling a wide array of foods and resources. That includes managed honeybees — which pollinate plants that provide a quarter of all food eaten in the U.S., accounting for more than $15 billion in increased crop value per year — but also many less famous wild species.

About 87 percent of all flowering plants rely on pollination by bees or other animals, often pinning their hopes on just a few local species. Yet many important pollinators are now in decline around the world, a crisis that is widely linked to human-related trends like habitat loss, pesticide use, urbanization and invasive species. This has sparked urgent efforts to save bees, butterflies and other pollinators, including campaigns to curb insecticide use or restore swaths of native prairie.

Big projects like those are important, but the new study also hints at the collective bee-boosting power of individual landowners. According to co-author Joan Milam, an ecologist and bee expert at UMass Amherst, these findings highlight how easy it can be for ordinary people to help bees. "I was amazed at the high level of bee diversity and abundance we documented in these lawns," she says in a university statement, "and it speaks to the value of the untreated lawn to support wildlife."

The "untreated" part is key to that value, adds co-author Alexandra Contosta, a post-doctoral research associate at the University of New Hampshire. "There is evidence that even though lawns are maintained to look uniform," she says, "they may support diverse plant communities and floral resources if the owners refrain from using herbicides to kill 'weeds' such as dandelions and clover."

While this is promising, the new study does have some limitations, its authors point out, and it's just one piece of a puzzle we're still putting together. "We acknowledge our small sample size and the study's limitation to suburban Massachusetts," says co-author and Arizona State University ecologist Christofer Bang, although he adds "the findings may be applicable in all temperate areas where lawns dominate."

The findings may also help erode the laziness stigma for non-weekly mowers, since the every-two-weeks approach could appeal to people who aren't obsessive about grass height but aren't ready to embrace the no-mow movement, either.

"While I would never 'let my lawn go,'" one of the study participants says, "I can certainly let it get a little higher than my neighbors' lawns and not feel guilty."