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irrigation design basicsIrrigation is not an essential part of a landscape. You don’t have to irrigate a landscape. Your good plant choices and proper timing for planting will help the plants do alright without irrigation. Irrigation is for landscapes where you want a higher level of quality. Plants love having a reliable source of water. The amount of irrigation you need is dependent on what level of plant quality you are willing to accept.

Compromise is an important word for irrigation design. A perfect design provides even, head-to-head coverage. Good irrigation design, though, reduces that coverage by omitting heads in low-moisture requirement zones like mulched beds under trees and along the edges of buildings.  Check your design to see if there are ribbons of landscape that can make do with a row of heads on only one side. Narrow strips of land between a sidewalk and a curb can be planted in a drought-tolerant grass and may need no irrigation at all. On steep slopes, consider running a line of heads at the top of the hill and allow the water to run down the slope. This can provide adequate coverage all the way to the bottom. Adequate is acceptable in many circumstances. Consolidate high-moisture requiring plants and irrigate only what has high needs.

You need to design with compromises because some zones in the landscape are difficult to access or the plant material is not worth the extra cost. On public projects, irrigation may not be allowed. The budget may be limited. Irrigation systems deteriorate. Without regular maintenance, an irrigation system might last only a couple of years before leaking and damage cause it to be turned off permanently. Your

landscape planting design should count on this happening. If the plant material isn’t fairly self-sustaining after two years of root establishment, then it isn’t a good choice for the site.

Automatic Sprinkler Systems

People install automatic irrigation systems because they want to avoid dragging garden hoses around the yard during droughts. Controllers can be set to run every single week. This doesn’t make sense for the landscape, though. If you irrigate every week without fail, the plants in your landscape will never develop deep roots. For stronger plants, set a system to run through all the zones only when you manually start the process. Run the system only when the plant material begins to show drought stress—gray foliage, crisp leaves, minor wilting. That way your plants become strong and healthy and send down deep roots.

Automatic systems are divided into zones, separated by type and sized according to the feeder line capacity and pressure loss. For a one-and-a-half-inch meter, you can comfortably feed about ten gallons per minute per zone. For a two-inch line, you can run zones less than twenty-five gallons per minute. This limits the number of heads per zone, based on the precipitation rate of the heads.

Heads are configured to different radii to fit the site. On some heads, different nozzles can change the pattern from a circle to a square or rectangle. The ground shifts with equipment running over them and weather fluctuations. The connections between the heads and the pipe should be flexible—either a jointed arm or flexible pipe connection.

Turf heads have a lower precipitation rate and should be run for fifty to sixty minutes. Shrub heads have a higher precipitation rate and their zones should only be run for five to ten minutes. Shrub zones in heavy clay soils can handle only a few minutes of watering from high-precipitation-rate heads before they stop receiving supplemental water. The excess drains away.

All the zones are tied together by feeder lines, with an electronic valve at the beginning of each zone. Electric current needs to be run to each valve, but this can be a challenge in some situations, especially urban streetscapes. Remote-controlled valves are available. Valves are much easier to service if they are located in a multi-manifold configuration, consolidated in one area. Valves should be placed in valve boxes, lined with gravel in the bottom, so they can be maintained easily.

Looping a feeder line can reduce the pressure loss within the system significantly. Large feeder lines might require support using thrust block reinforcement at sharp corners. Without it, the momentum of the running water to break the line.

The meter assembly that feeds the system should include a backflow preventer, with a manual cut-off valve in case of emergencies. A broken, two-inch feeder line makes a beautiful fountain, but the damage water under pressure can do is extensive and expensive!

Typically, without an initial pressure of sixty-five pounds per square inch, an underground sprinkler system cannot provide enough water for the heads to work. The final head at the end of the zone should receive a minimum of thirty pounds per square inch. If you have very low pressure, a pump may be required. If you have pressure over one hundred pounds per square inch, you may need to add a pressure regulator, to calm things down.

Drip

Drip systems are best for agricultural crop situations. An emitter must be located next to every plant, so a grid of small emitters in above-ground piping must be installed over the landscape. It is too much piping for large-scale landscapes. Each and every emitter must be kept free of debris or soil that might clog the emitter. That’s a lot of intense maintenance, especially in areas with heavy clay soils.

In public landscapes, vandals pull up the feeder tubes to tap into a water source. Since the system runs under a layer of mulch, it is difficult to know when there is a leak. For roadside situations, the leaking water might damage the road paving and sub base long before the leak is discovered. Little animals like to nibble on the tubes, too. The cons for drip irrigation for ornamental public landscape projects outweigh the pros by far. It is best to stick with pop-up sprinkler heads with shrub and turf heads for larger landscapes.

drip lines don't work

Home Grown Alternatives to Expensive Irrigation Systems

Homeowners who want to save money can combine quick-connect couplings, sprinkler heads, and garden hoses for a make-do system. Home hose bibs can run about two sprinkler head at a time on a timer, with garden hose acting as the feeder line, the hose can be connected to one set of two heads and then moved to another. The sets, connected by shorter lengths of garden hose, can be left in place in mulched beds and out of paths. Run each set about sixty minutes during periods of extreme drought to keep the landscape alive. Use sturdy, metal sprinkler heads. The plastic ones last for only one or two uses.

Plants need about one inch of precipitation each week during the growing season. They will let you know when it is time to provide supplemental water. Standing with a garden hose for a few minutes is not sufficient. Try timed sprinkler heads if you can’t afford an automatic, underground system. You might find it works so well, you never need to upgrade!

Irrigation