[A reader asked me to do an edited down version of this article to make it more accessible for those less interested, but in need of its message. This is a stab at that.]
The suburban American lawn has been identified with the fall of nature by many. Today, a good and green American, certainly us Portlanders are included in this, rejects the perfect monoculture of the lawn. Nature:good; lawn:bad. Our lawns demand water that could be better used growing food and assuring healthy fish populations, our lawnmowers spew air pollutants damaging to us all, our fertilizers leach away and move off site contaminating ground water and stream flow while our pesticides used on them, more directly attack nature all around us, all of this for no justifiable benefit, only fulfilling some narrowly defined human desire for an outdated aesthetic. Detractors of the lawn argue against the waste of resources they require and they are difficult to justify if their purpose is restricted to providing a neat and ‘defensible’ perimeter for each house, the appetites of golfers and the youthful fantasies for power and dominance of sport, all increasing the consumption of land ‘stollen’ from nature to sate our hunger for it. But this view of the lawn does it a disservice.
It rejects the understanding that when it is green and healthy it provides some degree of environmental benefit as well as for certain of our human needs. It ignores the fact that lawns fulfill other very necessary psychological and social needs in a human community that increase with the physical size of a city and its density….and, it ignores the fact that if we want a living ‘turf’ for varied activities it is the best surface, more durable that any other planted surface, that we can create or that nature could provide us. Anything more durable will have to be manufactured. Concrete, asphalt and built structures don’t fulfill all our needs as the price of real estate pushes nature out of most of our reaches. Ignoring this minimizes some of what it means to be human. Our lawns, our most intimate level landscapes, those we relax on and our children play and romp over, fulfill very real needs in human beings. But when these are regularly allowed to go brown, to go summer dormant, they lose much of this value and become more of a detriment to our other landscapes.
Lawn – its composition and growth… its ‘strengths’ and weaknesses
I need to dispel the idea that removing summer irrigation is ‘neutral’ regarding the health and composition of a lawn. It doesn’t work like a light switch, simply on or off. A lawn, as simple of a plant community as it is, is still alive and dynamic, responsive to everything that happens in and around it.
The primary component of a healthy lawn in the Willamette Valley is Perennial Rye Grass. The grass seed industry has spent time and resources selecting grasses that perform best in our soils and climate to grow a durable turf to meet both the passive and more active needs of humans living in compact, modern, communities. Just like other plants there is no ‘one size fits all’ when it comes to lawn grasses. In Central Oregon, in the high desert country east of the Cascades, where I spent the first half of my life, it is Kentucky Blue Grass that has been the best choice. Not here. Plant that here and, even with the best cultural practices, it will die out yielding to what ever is available immediately. Leave Kentucky Blue unirrigated with the much less abundant water to our east and its coarser/sandier soils and it will fail quickly there as well. Perennial Rye Grass, grown well here, ’tillers’ and thickens, but it can’t do it on its own, in our dry summer climate. It can’t do it without regular irrigation, mowing and fertilizing.
Seedling rye grass plants increase themselves vegetatively by ‘tillering’. From each crown additional stems form capable of forming new plants, roots, leaves and flowers from the nodes along these stems, creating a denser turf when soil moisture and nutrients are adequate. When soil moisture drops below this level, the plants go into a conservative mode and do not expend energy on tillering and spreading. Instead tillering stops and rooting goes deeper leaving remaining individual plants more isolated from one another. In a sense, a healthy, vigorous Perennial Rye Grass turf, is suspended in a kind of juvenile, expansive state, consistently attempting to spread in and cover open areas. This takes a great deal of resources. You have to provide it with what it needs in order for it to perform. A dense turf, having had its summer irrigation schedule disrupted, puts each rye grass plant into competition with all of the others for water. Inevitably some will weaken, losing any advantage that they may have had and dying, thinning out their population, while the remaining ‘stronger’ plants more successfully ‘chase’ the water down through the soil profile, at least as far as they can. Lolium perenne roots relatively shallowly, in a healthy turf, only 6” or so. This thin top layer dries relatively quickly here. Once the available soil moisture retreats beyond the reach of their roots, these individual plants will wilt and begin to weaken and die as well.
Lolium perenne, is a very resilient, tough plant, when grown well, characteristics that serve it as a turf grass. When it has access to what it needs it can be a very capable invader of adjacent landscapes. This is a common characteristic of many selected urban plants because of the generally inhospitable conditions prevalent in many urban landscapes. Such plants are tolerant of the abuse that these places are routinely subject to, most aren’t, which is why this was chosen, but it isn’t ideal here. If we got regular, significant, rains during our summer growing season, it would be better suited. Our maintenance practices must compensate for this. By cutting off summer irrigation to a perennial rye grass lawn we are removing an essential element for its growth and survival…which compounds the difficulties it already faces. Over time the Rye Grass dies out and is replaced by a mixture of the most dominating weeds available in the immediate area including other grass species, broad-leaved perennials and annuals as well as woody plants and vines. In general these turf weeds are plants that tolerate seasonal drought, the compacted soil conditions common to all lawns and the often nutrient deficient conditions common to them. What can grow, will grow. These become radically degraded landscapes. They are not the lawn they once were.
Lolium perenne is often referred to as a cool season grass, because it continues to grow well into the fall and winter before freezing temperatures set in in earnest. It follows the C3 metabolic pathway and, because of this, is not very water thrifty, by grass standards. Many grass species around the world follow the C4 pathway which is more ‘thrifty’, requiring less water and can tolerate more heat than can this species of Rye Grass as well. This grass initiates growth early in the spring when cool temperatures predominate. In hotter parts of the country it will struggle and weaken in summer’s heat, but is often seeded in the Fall by sports teams because of this ability, providing a durable, playable surface and extending a surface’s useful season. The warm/hot season grasses that provide a good surface all summer quickly decline in the cool of Fall. This ‘strategy’ is a particularly labor and resource intensive one. It requires a commitment. Perennial Rye Grass is chosen for this application because of its durability to play, in cool weather. When it is planted once and expected to perform consistently through out the year, year after year, it requires frequent irrigation in dry summer climates. Perennial Rye Grass is a compromise. Turf grass can’t simply be applied, like synthetic turf is these days, and be expected to perform consistently, with or without active use, while not providing for its cultural needs…no plant can do this.
There are many grasses that are more tolerant of our growing conditions, but they lack the durability of Lolium perenne when well grown. Also many of these C4 grasses are taller in stature with deeper roots systems and don’t respond well to the frequent short mowings that provide us with the low turf that we desire. Some are bunch type grasses and don’t tiller, so they will never form a dense turf on their own. Others may be coarser in texture and so don’t lend themselves to use as a turf. While still others won’t hold up to the repeated regular foot traffic we expect our lawns to withstand.
Drought also effectively reduces a lawns ‘durability’. Stressed turf does not have the ability to recover from ‘heavy’ use, lacking the protective density and the ability to recover from ‘injury’. Use, then, by damaging the cover and integrity of the lawn, speeds its decline. Over the period of several stress filled growing seasons Perennial Rye will more than likely yield completely to weed species and these weeds cannot provide the ‘protection’ the soil surface itself requires causing it to erode and become more irregular and less playable over time.
Lawns, as landscape features, are particularly difficult environments. Lawns, as single species, landscapes, can’t exist in nature without our considerable interference. These are designed and intended as places for certain types and levels of human activity. Perennial Rye Grass, like any other plant, evolved in mixed, dynamic plant communities, in its case, meadows. It is relatively intolerant of shade and will quickly yield to other better suited species. It didn’t evolve with tree canopy unless the trees were very dispersed. It was a single component of a diverse system. Grown under the most ideal conditions this grass will still be subject to weed invasion because there are simply too many niches left available. Perennial Rye lawns degrade over time because of this…even when adequately irrigated.
The Willamette Valley was once covered beneath hundreds of thousands of acres of wet and dry prairie, Oak Savannah, Woodlands of various densities and forest lands supported by soils that ranged from very rich deep alluvial soils to very thin mineral soils atop basalt formations. Perennial Rye Grass is a low growing relatively shallow rooted grass. Prairies and Savannahs, with their species diversity, occupy a greater depth of the soil, are more attuned to the seasonal cycle of precipitation, and are able to bring water back up from greater depths, while deeper rooted species capture and retain nutrients leached beyond the reach of others, returning them over time by the shedding of roots and top growth. In such a healthy system few nutrients are lost. Soils, and the plant communities upon them, in fact, tend to stay in balance or increase in richness over time. This all changes, is degraded, as soon as a diverse plant community is stripped away.
Replacing it with a vastly simplified monoculture like turf, allows much to be lost. Other abiotic factors, like the solar energy to power growth from the sun, continue at the same level. Absent the ground level diversity and layers, much of this sunlight is now available to power the growth of other plants, either weeds or more desirable community constituents. Several key abiotic conditions on a site remain largely the same and a single species landscape, like turf, cannot utilize them all. The energy remains free to other plants that can avail themselves to it. Taller plants, deeper rooted plants, plants that can take advantage of resources that the Rye doesn’t both when it sits dormant and is in active growth. As other plants move in the composition of the community changes. The Rye may disappear completely and its absence be masked by the occupation of weedier and more aggressive grasses. Owners may still have it regularly mown so that it serves some of the original function, but it is not the same. The exposure, the reduced level of care, the species now occupying the space, have themselves changed the growing conditions in the lawn and for the surrounding landscape. Over time these changes continue to accumulate and new invaders, available in the immediate area, move in. You cannot simply turn off the water and magically become ‘green’.
A degraded turf landscape, which is standard fare in much of Portland, may free up some water for other uses, or to remain in streams and the aquifer, but such landscapes, generally, provide unattractive spaces for our ‘social’ needs as people, as places to relax or a good surface for our more active pursuits, nor does it meet the needs of a healthy and diverse population of local fauna. These degraded turf landscapes support a population of aggressive weeds that possess relatively poor wildlife value. Were these landscapes left unmown and taller weeds and species allowed to mature, flower and set seed, its value would perhaps be greater for birds and wildlife, providing nesting cover, and food for more adaptive species, however, this would place an even larger weed seed burden on all other area landscapes, including turf, agricultural lands and the remaining intact and recovering native plant communities. Lawns, done well or poorly, are inherently very unstable, leaving many niches unfilled.
While many argue, rightfully, that the model single species healthy lawn provides very little habitat value, it does provide human value as a desirable place for activity and relaxation. Healthy turf cools and softens the surface of the soil making it more desirable and comfortable. Both allow excess rainfall to percolate down through the soil helping recharge the ground water which is otherwise greatly reduced across our redeveloping and denser city. The idea, that many homeowners have, that turning their lawn sprinklers off is an unmitigated good, is wrong and demonstrates their lack of understanding of what is being lost by making that choice, as it undoubtedly does lead to the decline of these landscapes and increases the weed pressure on all others.
Homeowners and turf managers must keep in mind that other important factors that control and limit a lawn must also be considered and compensated for. Lawns are walked on, sometimes driven over, which leads to soil compaction which limits the ability of roots to penetrate it and access what they need. The shallow root systems of a single species lawn draw heavily from this shallow soil layer in terms of nutrients while nitrogen not picked up washes down more deeply and is lost. Whether we recognize it or not even a lawn is a complex system and our choosing to ignore this does not make it any more different. Lawns will degrade with inappropriate care.
Regardless of what we do, there will always be ‘weed pressure’ on turf areas, especially in urban areas. Turf is an aberration in nature, an over simplification of the landscape. Ignoring it, stopping necessary summer irrigation is not a neutral act. Urban landscapes and soils have a long history of weed invasion and this history can be read in part by examining the seeds that are available in the local soil seed bank. The more weeds that have been introduced to a given area, the longer they have been on site producing generations of seeds, the more thoroughly contaminated the soil seed bank will be. As I’ve stated above a single species turf is perhaps the most unstable and volatile landscape that we can have, barring only bare soil. These seeds will germinate when they can. Given the weakened state of most lawns and the vigor of weeds, invasion is inevitable. The only question is how fast this will occur. We are the only force potentially standing in the way of this. When we ignore our role and responsibility, it is only a matter of how long before the grass turf is completely transformed and lost.
It is one thing to maintain an out of balance landscape for our own uses…it is completely different to create such landscapes and, through our neglect, allow them to degenerate, putting all other landscapes under much more weed pressure, under more threat. In the end, understand that a healthy vital lawn is an asset to an urban community, when well grown. It can play a vital role. A drought stressed, neglected lawn, serves nether the ‘social’ functions that we need of it nor is it an adequate stand in for our lost meadow and prairie landscapes that once covered much of this place, fulfilling vital habitat roles for wildlife. A degraded landscape diminishes us all.