These days whenever we talk about urban living and its effect on the environment we hear terms such as carbon footprint, air pollution, surface runoff and a whole host of other terms that are used to measure or describe how urban life alters the natural environment. Residential living by definition is anything but natural. When you consider things such as roads, foundations and sewers, running cars, lawn mowers and leaf blowers, there is no question “life” as many know it has an impact on the natural environment.
The term “urban landscapes” is often used to describe the general trends when it comes to what plants people choose to grow and maintain in their yards. Aside from their aesthetic and by extension psychological appeal, plants are critically important in any urban environment because they produce tons of oxygen and filter pollutants from the air. While dense forests like the Amazon are called “the lungs of the earth”, plants in an urban setting are often referred to as the “lungs of the neighbourhood”. In densely populated areas that are comprised mainly of multi-family dwellings (apartments/flats/condos) sometimes the only option for plant life is to grow a “green roof” due to a lack of open land.
All levels of government maintain an active and important role in the establishment and maintenance of vegetation in urban environments. For example, many governments have spent millions either treating or replacing Ash trees infected by the Emerald Ash Borer. Due to their size and longevity, trees are some of the best oxygen producing plants available.
Aside from desert-type environments in the U.S. such as Arizona where growing and maintaining green plant life can be a challenge, most North American urban landscapes have always incorporated various forms of plant life. For the average homeowner, the plants they choose to incorporate into their own yard are based on aesthetics, ease of care and property value rather than what’s best for the surrounding environment. Beyond trees, one of the most obvious and by far the most widespread type of vegetation in any urban setting is grass.
There are other ground covers available, so why has grass established itself so prominently? Here a few reasons:
- Dense Growth Pattern: No other type of ground cover grows densely enough to crowd out other unwanted plants (weeds). The average residential lawn has a root system that if stretched out would cover a distance from Toronto to Montreal. There are few plants that can match this kind of density.
- Low Maintenance: Due to its low lying uniform growth pattern, mowing/trimming grass with a lawn mower is relatively low maintenance when you compare pruning other types of vegetation. Although mowing with a gas mower does produce low levels of emissions, that is more than offset by the fact that the clippings from a lawn mower could and should be mulched back into the ground; which precipitates a thick, healthy and dense stand of grass that creates no landfill waste.
- Extends Living Areas: Beyond the “look” of a nice lawn, as opposed to many other plants, grass provides a relatively flat (and plush) surface that provides a whole host of uses broadly covered under things such as sports, family functions and lounging. This is one of the main reasons lawns have become a way of life for many homeowners.
With the advent of pesticide restrictions across many Canadian jurisdictions over the last decade, grass and the perceived “obsession with the perfect lawn” have become very politicized. We’ve seen anti-lawn initiatives such as Xeriscaping in an effort reduce the amount of grass in urban settings. While Xeriscaping clearly has its place in arid or desert-like environments, it can be very effectively proven that an urban setting with less grass is worse for the environment.
At a recent presentation given by Michael Brownbridge, PhD Research Director, Horticultural Production Systems- Vineland Research & Innovation Centre, he described a failed water-saving initiative in the U.S.
“In a bid to save water, California State and local governments paid homeowners to replace their living landscapes (including turfgrass) with mulch, rocks, cactus and plastic grass. In areas where landscaping and turfgrass were removed the soil could no longer capture and filter rainwater, or hold it on site for trees and plants to use. The denuded landscape was the least effective water-saving measure.”
Brownbridge went on to describe grass as a sponge:
“Grass acts like a sponge because it slows down and absorbs runoff, prevents flooding and soil erosion by “holding on” to soil, acts as a natural filtration system, cleans the water it collects, reduces acidity, and breaks down harmful microbes and pollutants, keeping them out of groundwater supplies”
He also broke down the benefits of a 235 m² (2,500 ft²) lawn very effectively:
“A standard lawn (50’ x 50’) produces enough oxygen to meet the daily needs of a family of four. It removes atmospheric pollutants such as ozone, hydrogen fluoride, perosyzacetyle nitrate (eye irritant in smog). It also captures dust, smoke and other particulates and pollutants. The lawn is the largest carbon sink (CO2) in the US and Canada. The dense canopy and fibrous root system sequesters up to 7x more carbon than is used in its maintenance.”
The pesticide debate that led to the current restrictions across the country inaccurately portrayed urban grasses as chemical-dependent plants requiring copious amounts of water, fertilizer and other resources all for the vain and very “cosmetic” pursuit of a perfect lawn. As you have read, the facts couldn’t be further from the truth! While a homeowner’s motivations for a nice lawn remain primarily aesthetic, the process of creating a “perfect” or healthy, lush green lawn is very holistic requiring very little in the way of inputs or resources. Let’s take a practical look at what a 235 m² (2,500 ft²) lawn typically requires product-wise in a season:
As you can see in the chart, the largest quantities are fertilizer and grass seed. The fertilizer applied in this example releases slowly, feeding the lawn gradually without adding any additional phosphorus (already naturally present and usable in the soil). Slow-release granular fertilizer focuses on developing root growth as much or more than top growth, making the goal far more than “cosmetic”. Grass seed fills in vulnerable bare soil areas and stops encroachment by weeds, thereby minimizing the need for blanket weed control coverage.
There are many plants that are beneficial to urban environments, but again few provide the breadth of coverage of turf grass. Trees are great oxygen producers, but they take years to establish.
So next time you come across any anti-lawn sentiments, take pride in the fact that your thick, healthy and lush green lawn is going a long way to maximizing the capacity of the “lungs of your neighbourhood”. Your lawn is an oxygen-producing, air-purifying eco-system that’s far more than just “cosmetic”!