Mention the southwestern United States and visions of jagged mountains and sweeping deserts come to mind - maybe even a camel or two! Yet the area, when examined more closely, is as geographically varied as the balance of the United States. In Arizona, the northern part of the state can see temperature of -20 degrees in the winter while the summers regularly deliver days exceeding 115 degrees to those that live in the Phoenix area. In addition to the climate, soils vary greatly. Mountain areas are comprised of solid granite and shale while flat and expansive farmlands compare to any Midwest farm field in actual soil composition. These are the extremes that landscape and irrigation contractors deal with and tame each day in the American southwest. Add to the recipe a land that is often drought-stricken, receiving less than 5 inches per year, and it quickly becomes apparent that a very well designed irrigation system is not a luxury but a necessity to maintain hospitable outdoor environments in the American west. Designing an irrigation system in the southwest requires the designer to focus on insuring complete water coverage for turf areas while minimizing water waste. Overspray onto walks, streets and buildings will creates not only a mess but, in many communities, the excess water on the streets and walks can result in a citation from the city for ?EUR??,,????'??wasting water.?EUR??,,????'?? Shrub areas tend to be less formal in layout, so blanketing the beds with water is generally not recommended. Let?EUR??,,????'???s look at the challenges and practices most often used to landscape and irrigate the Southwest desert. In a desert region such as the Sonoran desert, rain cannot be counted on to keep the plantings alive. Without an effective irrigation system, the desert will remain a desert. And no one seems to want that in Arizona. Most challenges to installing an effective irrigation system involve the difficulties of digging. The other area of challenge is the actual design and placement of sprinkler and emitter heads. Desert Soils As previously discussed, there are many soils and combinations of soils in the desert. Due to the extreme temperatures, mostly in the summer, the land experiences a consistent drying effect. As the surface dries, moisture rises to the top levels to replace that which has evaporated. The moisture also pulls microscopic minerals and salts left from previous drying periods toward the surface of the ground. This process, repeated for centuries, creates a layer of very dense soil known as ?EUR??,,????'??caliche.?EUR??,,????'?? Caliche is comprised of dissolved salts and minerals often impervious to water penetration and alkaline in nature. These mineral laden layers of soil can extend very deep into the earth, making excavation and digging as difficult as digging in the tightest clay or rock areas. The most difficult area often requires the use of a backhoe tractor with a jackhammer attachment mounted on the digging boom, known as a ?EUR??,,????'??hammerhoe.?EUR??,,????'?? Many areas make regular use of trenchers with ?EUR??,,????'??rock saw?EUR??,,????'?? attachments to penetrate the soil for irrigation systems. Other areas can have soils comprised of a mix of soil, sand and rock. These areas are generally found in locations where dry desert river and streambeds have occurred and are now in the path of development. Trenching in these acres can be a bone jarring experience if you chose to use a ?EUR??,,????'??DitchWitch?EUR??,,????'??-type of trencher. Round river rocks rattle and roll in the trench until they finally pop out and roll down the line of spoils, adjacent to the digging areas. When the rock component is too difficult, the best solution is the use of a backhoe or mini-excavator. Remembering that everything that comes out of the trench is supposed to go back into the trench, these conditions can create huge challenges. Often, the soil must be screened to remove the larger rocks and debris. Our company maintains a large rock screen that is moved to the more difficult sites for facilitating the process. Some projects prove so difficult that sand is imported. It is used to ?EUR??,,????'??bed?EUR??,,????'?? the pipe and insulate it from the adjacent rocky substrate. The resulting screened materials are either hauled off-site or used for fill in creating mounded areas. In one project that was completed by our firm, we were able to avoid ordering 260 tons of drainage rock and replace it with the rock that was generated by our trenching operations. We often install irrigation systems in areas that are being re-vegetated. Re-vegetation is the idea of restoring native plant palette that has been damaged due to construction or overuse by the landowner. These environmentally sensitive areas require attention to insure that any additional damage will not be done. Utmost care must be used to minimize damage to the area as irrigation lines are snaked into it. This becomes a process of cautious digging through the mineral encrusted soils while drip irrigation lines are run to each plant. In these areas, there is no replacement for the century old method of ?EUR??,,????'??pick and shovel?EUR??,,????'?? work. Moving materials and equipment into these areas must be done carefully so as to not damage any existing vegetation. Watering desert or ?EUR??,,????'??drought tolerant?EUR??,,????'?? trees and shrubs can be a challenge as well. The general rule of thumb is to provide long durations of watering at less frequent intervals. The duration of watering is dictated by how porous the soil is. If the soil is very dense, the soil will quit absorbing water and run off will result. In more porous soils, watering can extend for greater durations. The intent of long watering periods is to force the root system to reach deep for water while leaching the natural occurring salts deep into the soil as well. As salts are leached deep into the soil, the planting medium can be maintained in a more neutral pH, resulting in healthier and healthier looking plants. The resulting root growth is healthier and more able to withstand the climatic extremes of the desert. All plants require some amount of water. Not all plants require the same amounts. Some trees, such as the majestic Mesquite tree (Prosopsis varieties), will take all the water they can get. Others are very sensitive to over-watering. The Ironwood will decline and die if too much water is given to it. Many desert trees and shrubs have developed a mechanism to absorb all the water that they can get during a naturally occurring rainfall. This natural mechanism is good if you are a plant in a desert or drought prone area. With the introduction of an irrigation system, these same plants ?EUR??,,????'??drink them selves to death?EUR??,,????'??. Such is the case of the spectacular Saguaro cactus. If given too much water, it will continues to take it all in until it splits at the seams. Often the difference between a tree surviving or dieing is determined by how well the tree pit drains. If the roots sit in constant moisture, the tree will eventually die from lack of oxygen and a resulting bacterial infection. In this scenario, management of the irrigation system is critical to the survival of the plantings. Watering trees and shrubs in the desert southwest can be accomplished by the use of drip irrigation systems. Unlike a bubbler or shrub spray system, drip irrigation requires the use of one emitter head per plant. Larger plants may require more than one emitter per plant. When installed, emitters must be sized to match the water requirement of the specific plant, relative to the other plants on the irrigation zone. Emitter heads are preset for the amount of water that each one delivers to the plant, so the correct head must be selected as the drip system is built. Because emitters are plant specific in the manner that they are installed, they must be placed in close proximity to the plant. It is also important that they are not too close as to encourage abnormal root growth, resulting in a root bound plant. Often when planting on slopes, emitter head placement must occur on the uphill side of the plant to guaranty that water will run to the plant instead of away from it. Another challenge to watering in a drought prone area is the presence of animals that view the irrigation systems as their source of survival. Often, rabbits and ground squirrels will drink from the drip systems heads. In the attempt to get water, they can chew through the soft polyethylene tubing, allowing the water to flow unmetered into the landscape. Our firm will always install the emitter heat below grade, leaving just the open end of the poly tube exposed at the base of the plant. This prevents the supply line and head from being damaged by thirsty animals and rodents. It also prevents the gardener from catching the emitter with his rake and damaging the system. Whenever I travel, I find myself looking in valve boxes and at sprinkler head placements. I guess I will always be curious, trying to understand how others do their work. The next time you visit one of the resorts or golf courses in the southwest, take a good look. You will be amazed at all that goes into making the Sonoran Desert landscapes some of the most spectacular in the world. Dale Micetic is a Phoenix, Arizona-based landscape contractor with Terrain Systems, a division of Grounds Control Inc.