Then there is its cooling influence. When the water drawn in by grass roots is released by its blades – the process called transpiration – it has an effect something like what happens when a human sweats. A Brigham Young University found that turf grass is about 7 degrees cooler than bare ground and 18 degrees cooler than asphalt. Plant more, healthier grass in cities, Mr. White says, and you can help counteract the heat-island effect that makes city dwellers suffer in summertime.
When he hears the claim that a lawn is a sterile environment, he can only laugh. Any lawn-care worker knows that grass is a haven for every kind of bug – grubs, ants, spiders, crickets, grasshoppers, mites, earthworms, beetles – not to mention the millions of microbes that feast on the root thatch and grass cuttings. A healthy, well-cultivated lawn is especially hospitable, supporting 25 to 40 grubs per square foot, compared with five to 10 for one that’s unhealthy.
The water that helps it grow, Mr. White says, isn’t wasted at all. It is transpired into the air or filters through into groundwater and flows into rivers and lakes. The maligned “synthetic” fertilizers that many homeowners use is only nitrogen, phosphorus and potassium, found naturally throughout the environment. To the grass, “it is just chemistry.”
Rob Witherspoon, director or the Turfgrass Institute at the University of Guelph, agrees that healthy grass absorbs properly applied fertilizers and fixes them in the soil, preventing large-scale polluting runoff. Farm runoff causes far more trouble.
As for pesticides and herbicides, Mr. White’s province, Ontario, and many municipalities across the country have banned them on lawns for health reasons that he considers bogus. Federal health authorities still consider them safe to use. But with a little tender loving care, he says, a lawn can grow just fine without them.
One knock against grass is hard to dispute: Kentucky bluegrass (scientific name: poa pratensis) is a non-native species, originating in Eurasia. But so are the starling and the house sparrow, the dandelion and horsechestnut tree. In a modern urban environment, most of what appears natural is introduced or managed. We can’t turn all of our parks and lawns into a xeriscapes, which in any case often need as much weeding and other maintenance as grass does.
Mr. White concedes that by planting a non-native grass in our yards, “we’re growing a plant in an incredibly inhospitable place but, if we can help it live, it will actually produce the very thing we need: a cleaner, cooler environment.”
Grass also happens to be nature’s best ground cover. In open spaces around houses or in parks, we need something to keep the earth from blowing away and to halt the natural progression from weeds to woody plants to bush that occurs when any natural area is left alone. Grass’s great virtue, says Mr. White, is its most obvious one. “It withstands traffic. We can beat it up, we can mow it we can put thousands of people on it for a festival. At the end of the day, it has its own ability to revitalize and re-establish itself.”
With more than 10,000 species, grasses are what the Encyclopedia Britannica calls “the most abundant and important family of the Earth’s flora.” Kentucky bluegrass and other turf grasses have evolved over time to be uniquely hardy. Because animals were always chomping on them – first in ancient grasslands, then in fields and paddocks around human settlements – they developed the ability to grow quickly after their blades were cut.
They also learned to reproduce without seeds. Left to their own, they will grow tall and produce seed heads, but they can also send out rhizomes: horizontal, underground stems that produce new shoots. That is one reason why grass keeps on growing even when you cut it before it goes to seed. Another is that the growing points, or meristems, of grasses lie at the base of the shoot, so that the stem can be cut and keep growing – a trick most flowering plants can’t manage.