Drip Irrigation For Commercial Areas

Walk into the irrigation department of a big box home improvement store in most parts of the country, and you will probably see hundreds of drip/low-volume products displayed. But be careful, a high percentage of those products should only be installed in residential situations. In order to achieve long-term success in public landscapes, commercial/industrial parks, high-traffic zones and/or places where vandalism is prevalent, it is imperative that the appropriate irrigation products are selected, and that they are installed in the correct manner.

One of the major advantages that low-volume (i.e. drip) systems have over conventional sprinkler systems is that they can be easily adapted to a wide variety of landscapes, and then customized to deliver water more efficiently. The site usage, soil type, and plant material size and spacing are all important factors that determine which products should be used, and where they should be installed. For example, in many wholesale nurseries, 1/2- and 5/8-inch poly tubing (rather than PVC pipe) and 1/4-inch micro tubing are installed above grade to facilitate the irrigation of container plants, which are frequently relocated or removed. This type of installation would be entirely inappropriate in a public park or easement where the equipment could be easily tampered with by passers-by, or disturbed by maintenance practices.

Below-grade installations
One of the more common ways to keep low-volume systems problem-free in public areas is to keep the irrigation equipment out of sight. The simplest way to accomplish this is to install as many components as possible below grade. This normally means using PVC pipe (rather than polyethylene tubing) for the lateral lines; and multi-outlet drip heads — installed below grade — for the emission devices. These drip heads are typically connected to the PVC pipe by 1/2-inch nipples (or swing assemblies), similar to those on conventional pop-up sprinkler heads. Quarter-inch distribution tubing is then run, sub-surface, from the drip heads out to the plant material, where it terminates (above grade) at the drip line of the tree or shrub. With this type of installation, the only components that are above grade and visible are the ends of the tubing, which should be secured by stakes and have insect plugs inserted into the tip of the micro tubing to keep them clog free. Most of the multi-outlet drip heads manufactured today are self flushing and pressure compensating. This means they require little maintenance and can be installed on long laterals while still providing excellent uniformity — even if the terrain is not level. They are available in a variety of flow rates, so that the water application rate can be tailored to suit the soil type present at different sites, as well as the needs of the plant material. Although most of these drip heads contain some type of internal filter, it is still necessary to install a 140-150 mesh disc or screen "Y" filter followed by a 25- to 30-psi pressure regulator downstream of the control valve to ensure long-term reliability. Of course, these components should also be installed below grade. Use rectangular irrigation boxes that are preferably secured with locking lids.

In-line emitter tubing
In-line emitter tubing is another low-volume option available to irrigate trees, shrubs, and ground cover, and is suitable for use in commercial areas. There are several versions available, but it is basically 1/2- or 5/8-inch polyethylene tubing with pressure-compensating drip emitters built into the inside of the tubing. The emitters are placed in several different spacings, and are available in a variety of flow rates. Professional growers have utilized in-line emitter tubing for many years — especially for irrigating row crops where it is usually installed approximately 6 inches below grade. In residential landscapes, it is often installed on grade, and then covered up by 2 to 4 inches of mulch. In commercial landscapes it is best to install in-line emitter tubing about 4 to 8 inches below grade. Although certain manufacturers claim to use self-cleaning emitters, for long-term reliability in subsurface installations it is recommended to install an air relief valve and automatic flush valve for each zone to prevent suction of soil back into the emitter. In-line emitter tubing easily connects to PVC pipe using the appropriate compression adapters or insert fittings. It is an efficient low-volume alternative to irrigate slopes or oddly shaped planters and hedges. It also works well coiled around the drip line of specimen and ornamental trees. Problems with root intrusion have been minimized by pre-treating the emitters with an herbicide, or by new emitter designs that contain physical or mechanical barriers to prevent root intrusion that may clog the emitters. Like other low-volume products, it is still necessary to install a filter and pressure regulator after the control valve, since the in-line emitter tubing operates best between 15 and 50 psi.

These are just a few of the many advancements and improvements that irrigation manufacturers have made to their low-volume product lines over the last few years. So, if you have hesitated to install them in the past due to durability and reliability concerns, you might want to give them a second look. If the right products are installed in the right manner, commercial low-volume systems can be low maintenance, and highly efficient at the same time.

Stuart Spaulding, CLIA, is technical service manager for DIG Corp., a Vista, Calif. provider of alternative power controllers and drip irrigation systems. Spaulding also has more than 15 years of field experience in commercial landscape construction. He is available to answer installation questions regarding DIG products at questions@digcorp.com.