Challenge in the Desert: Water-Efficient Landscaping

Water-Efficient Landscaping

Desert gardeners, urban planners, and highway designers combine aesthetics with water conservation.

Text by Eric A. Johnson Photographs by Christine Keith The desert continues to bloom, but there's a difference. A steadily increasing empha sis on water-efficient landscap ing is altering the appearance of Arizona's lowland commun ities, especially the Phoenix and Tucson metropolitan areas. The primary reason is the need to conserve a limited water supply, but there are other factors: the realization that such conservation does not have to mean sunbaked austerity; the appeal of relatively low-maintenance gardening; widespread and growing availability of attractive water-thrifty plants; and more efficient moisture-delivery systems such as drip irrigation. The return to conscious economy of water use, once a requirement of pioneer survival, is a recent trend in the inland Southwest. One of the pleasant ironies of life in Phoenix and the Valley of the Sun five and six decades ago was that-despite the Valley's location in the midst of the Sonoran Desert-its homes, farms, and industries enjoyed an abundance of inexpensive water. It flowed in sparkling canals from upland dams and reservoirs on the Salt and Verde rivers. The resulting oasis was one of the nation's most fertile and productive agricultural regions, its green fields framing towns of tree-lined streets and broad lawns regularly watered by flood irrigation. The dams and reservoirs are still there, but the population they serve has multi plied more than ten fold in the last half century. Farther south, Tuc son, the state's second largest city, lacked a similar reservoir and canal system but pumped its water freely from a huge underground aquifer. Early in the century, Tucson created its own oasis by massive plant ings of thirsty shade trees. But the rapid urbanization of Arizona since World War II, and especially in the 1970s and '80s, has converted great tracts of virgin desert and cultivated farmland to expanding cityscapes covered with buildings and pavement, creating "heat islands." Both Phoenix and Tucson have become measurably warmer since the 1940s. Population growth has increased urban demand for both water and energy, the latter notably for air-conditioning. Underground water tables have fallen, making pumping more expensive in Tucson and other parts of the state dependent on wells. All of these factors have encouraged Arizona's desert dwellers to reexamine their gardening and landscaping practices. Many now question the validity of trying to duplicate the verdant environments of other climes. Recognizing the positive if fragile characteristics of the desert scene, they seek ways to accommodate to it.

The results are ever more prominent. Sophisticated landscape design and imaginative low-water-use plantings flank miles of new freeways and expressways under construction in the metropolitan areas. Arterial avenues in a number of communities reflect a new emphasis on providing a pleasing yet low-maintenance "streetscape" through the combination of structural elements and drought-tolerant plant materials. Individual commercial buildings and entire industrial parks, especially those recently constructed, boast handsomely tailored plantings of trees and shrubs. Such traditional "greenbelt" areas as golf courses are taking on a new look, the result of greater use of natural contours and native flora; revolutionary "target" courses, in fact, leave large areas of desert terrain untouched, to be leap-frogged by golfers on their tee shots. Meanwhile residential neighborhoods, once a continuum of Bermuda grass lawns, show varied design and material ranging from aesthetically delightful effects to, unfortunately, a "Western" kitsch that may celebrate a deftly placed cow's skull or a plaster of Paris burro, or even a rusting ox yoke carefully framed by white rocks. (No one claims that all landscape contractors, and all their clients, are cut from the same cloth.)

The best of the changes taking place result from revised attitudes, new awareness, and countless decisions large and small by home gardeners, property owners, urban planners, highway designers, legislators, and developers; and they affect not only the appearance but also the quality of life in our desert surroundings. Increasingly those decisions are influenced by experienced and knowledgeable professionals, especially as they pertain to new urban development: landscape architects, plant nurserymen, university researchers.

In their publication Desert Excellence, landscape architect Steve Martino and architect-planner Vernon Swaback argue for caution and balance in the development of desert communities: "Each day we are made aware of the difficult man-nature relationships in developing one of the world's most beautiful and sensitive environments. The issue is not the desert versus development, but rather how to develop communities which have as their unique character the special qualities of the desert. Stewardship of this land is not served by being 'for' or 'against' the myriad of issues that confront us daily. It is a matter of learning from the land and applying those lessons with increasing sophistication. Development means change, and if it is accompanied by understanding, the change can be for good.

"The term 'desert landscaping' means different things to different people. To some, it means a lonely cactus awkwardly placed in a sea of green gravel. To others, it means the desert untouched by man. The first view is simply absurd, the second often irrelevant to the problem at hand. The natural landscape is one which, by way of appropriate selection, placement, and handling of plantings, succeeds in expressing the indigenous nature and ecological processes of the region." If you live outside Arizona but occasionally visit here, you have surely noticed some of these trends. If you live here, you may well be one of the decision makers. And if you are a home gardener, you are probably especially conscious of the subject this month; for unlike the schedule prevailing in many parts of the country, this is planting time in the desert: the season when weather conditions are right, soils remain warm and hospitable, and the creative urge to get active in the garden touches us once again after the long, hot summer.

Water-Efficient Landscaping

expressing the indigenous nature and ecological processes of the region." If you live outside Arizona but occasionally visit here, you have surely noticed some of these trends. If you live here, you may well be one of the decision makers. And if you are a home gardener, you are probably especially conscious of the subject this month; for unlike the schedule prevailing in many parts of the country, this is planting time in the desert: the season when weather conditions are right, soils remain warm and hospitable, and the creative urge to get active in the garden touches us once again after the long, hot summer.

You are conscious of all this if you have lived and gardened in the Arizona desert for some time. But if you are a newcomer, suddenly facing the challenges of a climate different from any you have experienced before, you may well be looking for advice.

One basic bit of guidance is this: whereas it is important to be conscientious about water conservation, you don't need to overreact and pave your property with unbroken expanses of rock or gravel. Such solutions, in fact, add to the urban "heat island" problem and run up your air-conditioning costs. Limited areas of lawn or other dense green ground cover are quite defensible, especially when located where they help to moderate temperatures outside your house and thus reduce the amount of energy needed to heat or cool the interior. Indeed, thought-ful placement of trees, shrubs, and ground covers (including grass) to help control your immediate microclimate is one of the best reasons for a carefully designed landscape plan-as important as the aesthetic purposes, and more significant where your household budget is con-cerned. Such a framework of plantings, especially if the trees shade house walls, can greatly moderate summer heat; and savings in air-conditioning bills will likely compensate for the cost of the water.

Wise conservation, then, is not a matter of using little or no water in the garden but rather of making certain that what water you apply is used efficiently and economically.

Warren D. Jones, professor emeritus of landscape architecture at the University of Arizona, was an early proponent of "water budgeting" spending water where it will be enjoyed the most. Jones pioneered water-conserving landscape patterns, including the "mini-oasis," and in reshaping Southwestern gardeners' habits he defined a distinctive regional style of landscape design. The work of his many former students still reflects his ideas.

The mini-oasis concept advocates an enclosed patio or courtyard where favorite

Water-Efficient Landscaping

(ABOVE) Steve Martino and Associates landscaped the inner courtyard of a Scottsdale office complex called The Studio, designed by Vernon Swaback Associates. Native ironwood trees combine attractively with verbena, red salvia shrubs, and water elements.

(LEFT) Prostrate indigo bush rapidly covers slopes such as these on the Superstition Freeway (Tempe-Mesa). Its soft gray foliage harmonizes with mesquite trees and red bird-ofparadise. Many freeway plantings use water-conserving drip irrigation.

Continued from page 13 plants, even lush green choices, can thrive protected from the elements. Beyond this limited area, the rest of the garden or larger property comprises zones that accommodate various low-water-use plants.

Today the range of available water-thrifty plants is surprisingly broad. Far from implying simply cactus and a few other "deserty" specimens, the category includes not only dozens of attractive natives of the Sonoran Desert but also a large selection of plants from arid regions of Africa, Asia, Australia, the Middle East, and Latin America.

There is a common and understandable tendency on the part of new gardeners in the Southwest to want to reproduce the familiar verdant scenes of home-say, the Eastern Seaboard, the Deep South, the Midwest, or coastal California.

Depending on where the effort is made long-cultivated former farmland in the Salt River Valley is obviously more hospitable to such an undertaking than the caliche hardpan typical of Tucson-it is possible to reproduce the wide luxuriant lawns, broad-leafed trees, and lush shrub borders dear to nostalgic hearts. But the cost in water and maintenance will soon encourage investigation of a different approach that recognizes Phoenix is not New Orleans or Ann Arbor; and the advantages of a garden landscape that is more natural and more practical in the desert environment will become more and more apparent. University of Arizona research shows that appropriate plantings, carefully selected and placed, can benefit your pocketbook as well as the comfort and appearance of your home and garden.

E. Gregory McPherson, assistant professor of landscape architecture, and his associates created landscape situations in which the structures were identical but the surrounding garden plans were of three different types. These were labeled “mesiscape,” characterized by broad lawns and an abundance of moderate water-use trees and shrubs that did not, however, provide much shade; “xeriscape” (from xeros, the Greek word for dry or arid), designed to provide good summer shade from low-water-use plants; and “zeroscape,” in which decomposed granite covered all landscapable area, interrupted only by a few trees and shrubs that gave little shade.

The researchers' technical reports provide detailed data covering a number of variables (including the difference in water costs between Phoenix-the cheaper-and Tucson). But one consistent conclusion was that, although zeroscapes conserved the most water, the xeriscape plans were the most cost-effective in both communities because they resulted in much less energy consumption for heating and cooling than either the unshaded zeroscapes or the traditional mesiscapes.

The practical application of McPherson's study becomes increasingly significant in light of stringent conservation goals for the year 2000 established by the Arizona Department of Water Resources. “It will be necessary to select and locate plants judiciously to meet these goals while still providing the many benefits associated with vegetation,” McPherson stresses. “Designers will need guidelines to determine how much vegetation is needed to achieve a desired cooling effect.” Continuing research is proposed in order to provide such guidelines, including assessment of the relative performance of different species in regard to both water costs and energy savings. Certain facts are already well established. For example, broad trees that shade exposed walls are more effective than tall trees that shade roofs, because the former reduce the large amounts of solar heat gain that tend to come through windows and walls. And shade on a west wall in the afternoon provides greater energy savings than identical amounts of shade on an east wall in the morning. Tree form and crown density are significant factors; and so forth.

A sampling of water consumption figures, comparing costs of watering several kinds of trees of the same size, also emerged from the study. A 20-footwide California pepper costs three times as much to water as a mesquite of similar size; a mulberry costs five times as much to water as the mesquite. All the trees showed an exponential increase in water costs with increasing crown diameter.

McPherson summarized his report to a Berkeley, California, conference last winter as follows: “Summertime temperatures have risen dramatically in Phoenix and Tucson during the past 40 years, and urban canopy cover has diminished. One-dimensional policies that promote water conservation and reward conversion from mesiscape to zeroscape will exacerbate these trends. The result will be increased demands for cooling energy and landscape water, as well as increased carbon-dioxide emissions from power plants. One way to slow this 'vicious cycle' is through urban reforestation with low-water-use plants and xeriscape design.”

Water-Efficient Landscaping

If you are an Arizona desert dweller renovating your garden or starting a new garden from scratch, think about the following suggestions: Start by doing some concentrated reading, especially on the subject of xeriscapes. Then visit one or more demonstration gardens such as those at the Desert Botanical Garden in Papago Park, Phoenix (see page 30); the Boyce-Thompson Southwestern Arboretum near Superior (Arizona Highways, June 1989); the Tucson Botanical Gardens; and the Arizona-Sonora Desert Museum in Tucson Mountain Park.

Even if you plan to design your own garden, it's wise to obtain guidance from a professional landscape architect or consultant. Study the wide range of low-water-use plant material; talk to experienced nurserymen about specific plants.

Consider a mini-oasis, keeping the lawn area small. There are many attractive and practical ways to contour, zone, and plant the rest of the property. Remember that large gravel-covered areas increase reflective heat, collect debris, and eventually become weed-infested.

Learn how a well-planned irrigation system can save water. Group different plantings according to similar water needs. Low-volume bubblers and drip irrigation systems on computerized timers can provide accurate and easily adjusted applications.

Get advice on blending organic matter to improve soil structure, but remember that some native plants prefer less organic material in the planting mix. Caliche, clay, and very sandy soils call for special advice and treatment.Finally, remember that the desert's gardening calendar is different from what you may expect. It's Octoberand fall is planting time!