Straight talk about drip.
Sunset has been reporting on drip irrigation for nearly two decades. Some of our early reports were based on visits to farms in Israel, where irrigation pioneers were harnessing a then-new technology to water crops in an arid land. Today, drip systems water many home gardens in arid Western states. But as with any technology, drip irrigation is constantly evolving, presenting new possibilities--and puzzles.
To help demystify drip, we asked readers who had installed systems to share the challenges and surprises they encountered. We then presented these responses--many concerning cost, durability, and effectiveness--along with a few questions of our own to three California-based irrigation experts for advice on how to make drip work efficiently.
Their answers can help you decide if drip is right for your garden and plan an irrigation system that best meets your plants' needs, or solve problems with an existing system.
When is drip irrigation most practical, and when should sprinklers be used?
Tom Bressan: The most compelling situation for drip is in gardens of widely spaced shrubs and perennials. Drip also works in small, awkward planting beds, or narrow planted strips, which if watered with sprinklers results in overspray.
Bob Galbreath: One way to judge whether or not plants are suited to drip is by the size of containers they're growing in. Plants from 1-gallon containers or larger are appropriate for drip; plants from flats are better suited for spray.
Owen Dell: Put sprinklers on your lawn, and design the rest of your garden for drip. Use plants including ground covers) with individual root systems, rather than creeping types, like gazanias, whose diffuse root systems can't be effectively watered by drip.
How do drip-irrigation kits compare with custom-designed systems?
Bressan: Kits may seem cheaper than custom systems, but you frequently end up with components you don't need. The filter and pressure regulator provided with kits are often inadequate as the system expands. it's best to plan your system, then buy what you need in the quantities you need.
Galbreath: People are knocked over by the thousands of dollars a contractor might quote for an irrigation system when they compare it with a $350 kit that theoretically covers the same area. Remember, a contractor is designing a system to fit your specific needs, and he plans to install it once--correctly. In contrast, kits offer a lot of irrigation potential for the money, but they require the homeowner to tinker with the system on an ongoing basis.
As a compromise, you might design a custom system, hire a contractor to install the valves and underground pipe, then install aboveground drip components yourself.
Does it make sense to convert sprinklers to drip, or is it best to start from scratch?
There are two basic approaches to converting sprinklers to drip. One is to use multioutlet emitters that screw directly onto sprinkler risers, without the need for a filter or pressure regulator. Although the retrofit is quick and easy, it has drawbacks (addressed below). The second is a full drip conversion using existing underground PVC lines as a delivery system; adapt one or more risers for drip and cap the rest. A filter and pressure regulator are required, usually best placed directly after the control valve.
While our experts agree that multioutlet emitters have limited use, their opinions vary on the savings of full sprinkler conversion using existing underground lines.
Bressan: The large quantity and small size of the distribution tubing in multioutlet emitters can be a maintenance problem, since the tubing breaks and detaches easily and is vulnerable to damage from animals, foot traffic, and gardeners. This type of conversion is most effective in small areas watered by a few sprinkler heads.
A full conversion (using existing underground lines) can save time and money when existing valves are functional, areas have similar plants, soils, and exposure, and lines are PVC. Don't convert an old in-ground galvanized system.
Galbreath: If you're hiring a contractor, 9 times out of 10 it's not cost-effective to convert an old system. It is extremely time-intensive to explore underground pipes and joints to assess their condition. The portions of a system that may be worth saving (from a cost standpoint) are pipes that go under sidewalks or driveways. Most experienced contractors want to start from scratch using the best available materials.
If you plan a do-it-yourself retrofit, shrub borders around the house are perfect candidates for drip. If a portion of your lawn is on the same valve as the shrubs, you're going to have to give up that portion or skip the retrofit, since lawn cannot be drip-irrigated effectively. You usually can't justify the cost of a conversion by converting only for shrubs. The lawn will probably still be the biggest water user, and lawns require sprinklers.
Dell: It's not practical to convert lawns to drip. And, in situations where plants are overgrown, it may be physically difficult to get drip tubing in place, unless you cut plants back.
The plants you are converting from sprinkler to drip have developed root systems accustomed to diffuse overhead irrigation. When you change to drip, you change the water pattern. To help plants through the transition, make the conversion in winter when rain is likely. As you move into spring, use drip and keep an eye on the plants, particularly trees, which may need some overhead water during the warm season. By the second year, use drip only.
If you are covering long distances with drip, or if you need to carry more than 4 gallons per minute (gpm) of water through 1/2-inch tubing (that's 240 1-gpm emitters per line), it pays to use existing PVC pipe as feeder line and tap in aboveground with conventional 1/2-inch drip tubing.
This strategy has several advantages over multioutlet emitters: you have more flexibility since you can put your drip tubing anywhere (not just at existing sprinkler heads); and, by inserting emitters directly into sturdy 1/2-inch tubing, you avoid the maintenance and potential physical hazards associated with protruding multioutlet tubing.
An alternative for small gardens where plants are close to the valve is to abandon the existing underground pipe and just use the existing valve; add a filter and pressure regulator and run the 1/2-inch drip tubing with emitters aboveground. Remove and cap off the sprinkler heads from the old system but leave the pipes in the ground.
How do you estimate the cost of a new drip system?
Bressan: Make a sketch of your yard, and map out the drip system. Determine the length of tubing and number of emitters needed. Decide how many planting zones you need to irrigate, and then decide if they will be automated. Automated zones require valves and a time clock. Take your plan to an irrigation supply store, and get help computing costs. This eliminates excessive trips to the store and, since you can buy in bulk, the penalties of small packaging.
The cost for most drip systems, excluding timer and valves, but including filter, pressure regulator, tubing, drippers, and accessories, falls in the range of $50 to $150 per zone. The cost of the drip system is less dependent on coverage area than on the number and density of plantings.
Dell: Drip systems are not cheap. Generally, budget as much for drip as you would for a sprinkler system; with drip, the cost savings result from saving water. (A well-managed drip system uses only 20 to 50 percent of the water a typical sprinkler system uses.)
Compared with sprinklers, drip offers additional hidden savings: it doesn't water the house (as many sprinkler systems do), which minimizes home maintenance, and there is no spray onto paved surfaces, which can be a slippery hazard.
If you're doing the installation yourself, work from a design to estimate costs. if a contractor installs the system in a new landscape, the cost per plant is about $2 to $3, plus your drip setup, which consists of the valve, pressure regulator, and filter. The drip setup ranges from $100 to $300. (A controller costs extra.)
How do you minimize maintenance?
Our experts say that proper design and installation ensure a trouble-free system. Maintenance should cost only a few dollars each year if you do it yourself. Shop where the professionals go, and use top-quality products. Prepare a sketch of your landscape, noting the water source, plants, and dimensions, and take it with you when you shop.
If your system is complex, call a landscape contractor, landscape architect, or irrigation designer for advice--even if you plan to install the system yourself.
On the subject of specific components, our panelists agree that a pressure regulator and a filter are essential. Minimize the use of minisprays and 1/4-inch or smaller tubing.
Bressan: To minimize damage from animals or cultivation, use as little 1/4-inch spaghetti tubing as possible. Self-flushing drip emitters are the least troublesome; minisprays on stakes are the most vulnerable. Emitters shouldn't clog if you use a filter and flush the system once a year. If you are placing emitters underground, use types designed for that purpose.
Galbreath: Filters collect particles from the water, preventing clogged emitters. In rare cases, insects or bacteria may cause emitters to clog. If insects are a problem, use special emitters with bug caps. If you suspect unusual water conditions, such as bacterial iron slime, ask your county cooperative extension agent for advice.
To prevent components from leaking or blowing apart, regulate the water pressure (addressed later), and use tubing and connectors from the same manufacturer.
Dell: Don't use spaghetti tubing or minisprays. Place emitters directly along 1/2-inch drip tubing. Install the emitters on the side of the tubing, instead of on top, so that if the tubing gets stepped on, the emitters are less likely to break off.
Put the tubing on the ground, and cover it with several inches of mulch. To prevent the tubing from buckling between stakes and popping up out of the mulch, place wire hairpin anchor stakes at 1-foot intervals along the tubing (rather than the recommended 4 feet or so).
When attaching emitters, use a punch that removes the plug of tubing. A good fit prevents components from leaking or blowing apart; use a punch with interchangeable heads or one designed to be used with your emitters.
Try self-flushing end caps; they flush some water at the beginning and end of every watering period so you don't have to flush the lines annually.
Usually it's sufficient to clean your filter once a year at the beginning of the watering season. In rare instances, the filter may need to be cleaned oftener. If you use well water that is full of sediment, you may need to use extra filtering at the well to keep the system clean.
How do you regulate water pressure so the system won't blow?
Most low-volume systems are designed to run between 20 and 30 pounds per square inch (psi). Since household lines generally range from 50 to 100 psi, even up to 300 psi in some areas, you need one or more pressure regulators to reduce pressure so it won't cause leaks and blow fittings apart.
Galbreath and Dell echoed each other's advice, which is summarized here.
First you need to rent (from an irrigation supply) or buy a pressure gauge that measures static pressure (the pressure pushing against the pipe when no water is flowing through). To measure, hook the gauge up to a hose bibb and open the spigot. If your pressure is less than 80 psi, a plastic pressure regulator preset at 20 or 30 psi will do.
If your pressure is more than 80 psi, consider installing a heavy-duty master regulator near your main shutoff valve to drop the supply pressure down to a manageable 55 to 75 psi. Then put a separate preset regulator downstream from each valve to reduce the pressure to 20 to 30 psi.
The master regulator should be installed by a plumber or landscape professional. Braukmann and Wilkins are two recommended brands of heavy-duty pressure regulators.
What causes low water pressure and variable pressure?
Low pressure is caused by trying to use more water than the source can provide. Pressure loss along the lines is caused by too much flow for the tubing size or lines being too long. Variable water pressure can be caused by changes in elevation along the lines.
Bressan: If pressure is low throughout the system, don't try to exceed the gallonage of water that your source can provide. As a general rule, limit your system to 70 percent of available flow.
To determine flow, turn on your hose bibb or valve full force and measure the flow in gallons per minute (gpm). If you use a 5-gallon bucket that fills in 30 seconds, flow is 10 gpm. If you have 10 gpm, you can use 7 gpm, which is 420 (7 x 60) gallons per hour (gph). The total gallonage of your emitters should not exceed that number. Leave a margin for future expansion of the system.
To avoid pressure loss along the line, use tubing that's large enough to carry the maximum expected water flow for the required distance without excessive pressure loss due to friction. Calculate total flow by adding the output of all the emitters you plan for one line. A reputable irrigation supplier or manufacturer can tell you the flow capacity for different-size tubing. For most home systems, 1/2-inch tubing is sufficient.
Dell: The carrying capacity of 1/2-inch tubing is about 240 gph per line, or the equivalent of 240 1-gph emitters. Allow for additional emitters along the line as plants mature. If you anticipate a need for more emitters than a line can supply, run two lines from the valve. Or run additional drip lines from underground PVC distribution lines.
Bressan: If elevation changes cause irregular pressure, but the rise or drop in elevation is less than 12 vertical feet, pressure changes are not significant. When water runs down a steep slope, adjust the pressure by placing additional pressure regulators or adjustable check valves about every 20 vertical feet.
When water flows uphill from the valve, leaving inadequate pressure at the top, it may be necessary to take water at least partway up the slope in PVC pipe at full pressure; at that point, set the initial pressure regulator and run drip tubing along the contour of the land so that it remains level; the PVC can run up and down the slope.
How much water do plants need, and how do you give them what they need?
Our experts agree: when it comes to understanding plant needs, there is no substitute for knowing your garden environment, digging in the dirt to check soil moisture, and observing plants for signs of water stress. Even the best irrigation system can't manage water for you.
As a starting point, refer to the September 1988 Sunset article "Taking the guesswork out of drip irrigation," which includes a chart to help you determine how much water to give different kinds of plants. Copies are available for $2 each; send to Drip Reprint, Sunset Magazine, 80 Willow Rd., Menlo Park, Calif. 94025.
In addition, the Sunset Drought Survival Guide," reprinted from the May 1991 magazine, tells how many of which size emitters to use for different types of plants. Reprints are available for $2.50. (Send requests for copies to the address above.)
Dell: You can change the quantity of water a plant receives by adding or subtracting emitters, but you can't change the frequency or duration for an individual plant. So "hydrozone" your landscape; group plants with similar water needs.
Design the system to separate areas with different water needs based on plant type, microclimate, soil, and exposure. Having separate valves for separate zones gives you flexibility in terms of watering frequency. For instance, if you have a sandy area on the south side of a slope, you may want to water it twice a week. In clay soils on the north, you may want to water only once a month.
Plants in shade are usually zoned separately from plants in sun. But plants under the shade of a tree may be an exception; if tree roots are taking water from surrounding plants, the shaded plants may need as much water as those in sun.
Bressan: Through observation you can learn how little water plants need before they show signs of stress. To save water, decrease the frequency of irrigation and observe, over time, whether or not plants are stressed. If only some plants show stress, install additional emitters next to the thirstier ones, or zone them separately.
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|Title Annotation:||drip irrigation|
|Date:||Jul 1, 1992|
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