Strangely enough, the people of the region are not inhibited by the climate and desire a dynamic aesthetic highlighted by flora not native to the region. The region is covered with large parks, exotic gardens, unique landscaping and 100's of golf courses. Thus, one of the greatest challenges a Landscape Contractor has is bringing the right amount of water to a project to satisfy the inhabitants and their peculiar green thumb.

Soil Preparation

When creating a landscape, analyzing the type of soil, amount of water the soil will hold, and how well plants draw water through the soil are all factors the Landscape Contractor should take into account. The soil is the base for any landscape project involving plant materials and, often times, one or more of these factors is overlooked, which can result in brownspots and dead plant life. Porous soils, like sand, take water well, but hold on to very little of it. Clay soils tend to act like a strong sponge, but can only take so much water at a time, creating runoff. The trick is knowing the type of soil you are working with because it makes a big difference in how you design an irrigation system. "Soil is important in determining an irrigation schedule," explained David Pagano, Associate Editor/Irrigation for LASN and LCM. "The type of soil determines how much water the soil will hold. Take the Southern California desert. There is a lot of blow sand or sugar sand. It might only hold one inch of water per square foot. Clay soils, like in Irvine, hold maybe three inches per foot, but only two inches becomes available and there is a lot of runoff when irrigating for long periods of time."

One way to compensate for this discrepancy in both types of soils it the use of polymers. TeraWet is a non-toxic, potassium-based polymer which, when added to the soil, increases that soil's ability to retain water. Essentially, when soil tension is low, the polymer crystal, roughly the size of a grain of sugar, absorbs excess water and grows to up to 100 times its original size. This water is contained within the crystal until the soil dries and tension increases, draining the water from the crystal into the soil at the root zone, where it is readily available to the plant. "TeraWet is effective in arid climates for three reason," said John Abt, TeraWet President. "A) It lengthens the time between irrigations; B) It reduces water usage and reduces fertilizer usage because when applied with water, the fertilizer will percolate to the root zone and be captured by the crystals as well; C) It increases grass and plant growth. In agriculture uses, crop yields have increased 17-40%."

Controllers, Scheduling and Sensor Arrays

Finding a controller which can address a variety of irrigation programs is essential to most irrigation projects. Since soil and plant types vary greatly throughout the region, precise irrigation is sometimes needed to compensate. Sandy soils, for example, might need two extended periods of irrigation. Clay soils can hold more water, thus needing less irrigation time. But with runoff problems, a schedule which includes a series of short run times, reducing runoff and increasing the soils efficiency in absorbing water.

Weather also plays a huge factor in determining irrigation schedules in arid climates. Not only does scheduling need to work around the hottest parts of the day, it also has to adjust for more random weather phenomenon, like wind and rain. A sensor array which adjusts for random weather can help a controller reduce the amount of water wasted when the Santa Ana's are howling or thunderclouds are dropping much needed precipitation. "Rain sensors are a real good idea," said Dan Veyna, ASLA, President of Jardin Landscape Architecture and Construction. "There's nothing worse than when, in a water tight area, an irrigation system is running during a thunderstorm or in the middle of a steady rain."

There are two solutions for this problem. The first is a controller that is Evapotranspiration (ET) equipped. The ET rate is a measurement, based on environmental readings, which determines the rate at which water will evaporate from the plant and schedules to replenish the same amount. Moisture sensors, which are planted in the soil, may be the best option for irrigation regulation. Irrometer, for example, makes two types of moisture sensors. The most advanced is the tensiometer, which measures soil tension directly from the soil. "As the soil dries out, the tension gets higher which makes it harder to extract water from the soil," noted Dan Gonzalez, Vice President of Sales and Marketing. "It lets you know precisely what a plant's roots are seeing in terms of tension." The soil sensor can be equipped with magnetic vacuum gauge which allows or overrides irrigation. The other type of sensor is the Watermark, a more traditional sensor which measures how much moisture is in the soil based on how well an electrical current can travel through the soil. The Watermark, although less accurate than its sister unit, requires less maintenance and will work for up to 10 years in one location.

The Sprinkler vs. Drip

The often heated debate between contractors in the arena of irrigation usually focuses on which is better: sprinkler irrigation or drip. Depending on the project, both delivery systems have merit, sometimes in the same system.

Veyna, who works a lot in California's San Joaquin Valley, likes to use small pop-up sprinklers for his projects. The trick, he explained, is being able to place the sprinklers efficiently: "Make sure the coverage area of the sprinklers is as close to head-to-head as possible. Do not over space the heads because they won't cover the entire irrigation area. Don't overlap because overwatering is neither efficient nor healthy. A landscape professional should be fairly knowledgeable with plant materials and should be able to determine how much water each needs and dictate the proper coverage areas." Despite being efficient in coverage, standard irrigation practices are impractical because weather factors, usually wind, heat or snow, can drastically alter irrigation schedules. But the most serious problem is runoff, which is where drip irrigation comes in.

One reason, according to some irrigation specialists, that Landscape Contractors don't consider drip irrigation for a project is either a bad experience with drip or lack of knowledge about important factors surrounding drip irrigation. In some cases, a contractor installed a drip system and something went expensively wrong because of a maintenance mistake. In other cases, contractors believe installation costs, especially for sub-terranean installations. Netafim's Director of Landscape Kurt Maloney added, "I can be so bold to say, the kind of drip system we sell has a real advantage over spray systems. It saves water by reducing runoff and doesn't water sidewalks or driveways. We need to better help people understand the technology available and how best to use it. Once they understand the technology and design schemes for installation, they could improve their profitability on ever job."

Two of the major drip-line manufacturers, Netafim and Rain Bird Xerigation, both work on similar principles. Inline tubing, made of flexible polyethylene, is put either on or below the surface. Emitters, either added to the line or built-in, then introduce water directly to the root zone of a plant at a very slow, controlled rate, ensuring the roots will be stocked with enough water to last until the next irrigation cycle. "On the great debate, with drip irrigation, you wet a greater portion of the soil structure, allowing the roots to probe further into the soil. We've found with sprinkler systems, grass roots don't get very far from the surface."

Interestingly enough, the drip industry has its own heated debate about the best form of installation. Mike Baron, Director of the Landscape Division at Rain Bird Xerigation, explained, "I prefer to lay drip systems at grade and mulch over them. It is the most practical application and labor efficient. From a commercial standpoint, it protects against damage caused by burying the tubing." Baron noted the reason mulch was so important is that in arid climates, it keep water in the drip line cool under the summer sun.

Maloney believes a subterranean installation is the best route for drip irrigation systems. "The real advantage is it's out of sight and out of mind. It doesn't need maintenance checks, as long as the filters are kept clean. A lot of people seem to think installation costs more money, but for many areas, especially long narrow areas, this is just not the case." Both agree, however, that the one problem with subterranean lines is the threat of root intrusion, which is why both recommend chemicals which retard the roots ability to invade the tubing.

Essentially, the debates over spray vs. drip and subterranean vs. surface ultimately boil down to determining the project's size and needs. "It is all dependent on plant material and the project design," Pagano concluded. "Golf courses water with rotors all night. For an area with sparsely placed shrub material or plants with unique water needs, drip is the most efficient. But drip has its limitations since you can't use it irrigate a golf course with it." lcm