By Stuart Spaulding, CLIA
Over the past several years, micro-irrigation manufacturers have been quite busy producing new low volume irrigation products and improving on the extensive array of existing products available to the home gardener. There are now so many products and installation options available that it's easy to see how a consumer can get a little confused when it comes to learning which products to utilize, and how these products should be installed. But fear not! The good news is that the confusion can be easily minimized, and the residential gardener can install an efficient, unobtrusive, durable drip system, so long as the initial design is sound, and the correct products are chosen.
When it comes to drip irrigation systems, simpler is almost always better. The simplest way to start your drip system is at the closest hose bib to the areas to be irrigated. Because these efficient systems need clean water and low pressure, low-volume drip systems start with a filter and a pressure regulator, (which screw together), and this assembly is usually screwed directly on to the faucet. Tip #1: Make sure these components all have "hose" type threads (not "pipe" type threads). If the faucet is needed for a garden hose hookup, install a brass Y splitter on the faucet so that each side can be used independently. Tip #2: If the faucet is in a high visibility area, install this head assembly at the end of a garden hose, at ground level where it won't be so conspicuous.
So called 1/2" poly tubing is the primary supply line that delivers the water out to your plant material. It is run from the head assembly out through the areas to be irrigated. The poly tubing produced today by major manufacturers is durable, easy to work with, requires no glue or special tools, and contains compounds that make it resistant to the harmful affects of solar (UV) radiation. Tip #3: Be aware that there are actually several different sizes of 1/2" poly tubing, none of which have a diameter of exactly 1/2"! It's important to know the outside diameter of the tubing, so you can use the proper size fittings. Tip#4: Use either .700" OD tubing with .700" compression fittings (black insert) or .710" OD tubing with .710" compression fittings (blue insert). Both sizes are readily available at most suppliers throughout the western U.S. To simplify installation and maintenance, do not bury the tubing, lay it on grade with gentle curves for expansion/contraction, and secure it every 10 feet or so with a stake. Run it next to smaller shrubs, and coil it around the drip line of foundation shrubs and specimen trees. Cover it up with with 2"-3" of mulch if you wish to keep it hidden. It is a good idea to stay away from the smaller, 1/4" tubing as much as possible, and only use it when necessary, such as branching off to a plant in a container. Tip #5: Install all the emission devices directly into the 1/2" poly tubing wherever possible.
There are many types of drip emitters to choose from, but the most important thing to know is the drippers flow rate, which is measured in gallons per hour. Tip #6: Select the drippers flow rate based on your site soil type, not the size or species of the plants. Plants in heavy clay soils, which are common in the Western US, are best irrigated with low flow drippers like the 1/2 or 1 gallon per hour type. For lighter loamier soils, use a higher flow dripper like a 2 gph version, but stick with the same type throughout the garden. For larger shrubs or trees, simply use more of them per plant, and spread the water out over the entire drip zone. Always install a minimum of at least two drippers per plant.
In situations where there are many small plants close together, (i.e. flower beds or ground cover areas), forego drip emitters altogether and install micro-sprinklers on the edge of the beds directly into the 1/2" poly tubing. Tip #7: Micro-sprinklers and drippers may be installed on the same zone, but a separate zone should be installed to irrigate vegetable gardens.
Fortunately for the do-it-yourself gardener, today there is much more information readily available about the design and installation of water saving drip irrigation systems. Some useful books are available in the book section of your local nursery, and more material is posted on the Internet and on drip manufacturers web sites. If you do a little research, and remember to keep it simple, you will be able to install a durable, efficient drip system that will save water, and produce healthier plants at the same time.