Mowing grass in varying degrees of moderation to promote plants, landscaping or pollinators
According to my kindergartner, the lawnmower was “amazing.” The shiny red tractor appeared to have an air-conditioned cab, three wheels and as my son put it, “two cutters” for the grass. It easily made short work of the city park we were visiting, presumably leading to the reopening of a field that had been temporarily closed to the public to allow the grass to recover from the beating it took during Fourth of July festivities. This raised a question for my son though— why was it bad for people to walk on the grass that this amazing machine was now chopping with it’s impressive “cutters?”
Lopping off portions of leaves
To make sense of how grass withstands regular trimmings, it helps to note how grass is structured. The flat ‘blades’ we like to feel under our bare feet are leaves the grow out of a smaller stem just above the plant’s roots. Like the leaves on a tree, losing some percentage of these leaves isn’t as dangerous as damage to the stem. Unlike leaves on tree, grasses have evolved to regrow the cropped portion of a leaf, ensuring that the effects of a modest mowing are only temporary. This likely evolved to help grasses survive visits from grazing herbivores, helping keep the grass and the nibbling animal happy as long as the plant’s stem isn’t trampled.
Mowing for more density
Humans are generally less concerned with grazing on our lawns these days, but there are still plenty of thoughts on how to properly manage grass growth cycles. If one’s goal is to maintain an even, densely-packed lawn, it’s recommended that you trim grass every week. This is to keep any single blades of grass from overshadowing their neighbors, leading to uneven growth overall. There’s also a risk of overcompensating after a lawn has grown taller than desired, as removing more than a third of the grasses’ height at once is more likely to stress the plants.
Pausing for more pollinators
On the other hand, most of us don’t play golf and don’t necessarily need the dense, homogeneous botanical carpet of a putting green. If that’s an option, allowing a lawn to have a bit more time between trims can promote the growth pollinator-friendly flowers like clover and dandelions. Even if you’re not interested in saving time, mower fuel or making tea from your yard’s yellow flowers, allowing some flowering plants to bloom in your lawn may make a big difference to a variety of bees. In a study by University of Massachusetts Amherst and the U.S. Forest Service, honeybees, bumblebees, carpenter bees, leafcutters, masons and sweat bees were all observed taking advantage of suburban lawns, but only if the lawns were mowed on a less aggressive schedule.
This doesn’t mean you need (or should) give up on mowing your lawn altogether. Some lawns in the study were only mowed on three-week cycles, but they didn’t seem to be any better than their two-week counterparts. The cause for this diminished return wasn’t immediately clear, but researchers suspect that three-week-old grass may be tall enough to hide some of these flowers, and thus didn’t provide much of a boost to pollinators.
Source: Why 'lazy' lawn mowers are heroes for bees by Russell McLendon, Mother Nature Network