City of San Luis Obispo - Utilities Department

Dripping Faucet. Drip Irrigation
Drip irrigation can save an enormous amount of water. It is an ideal watering system for most kinds of plants, if it is done correctly. Water is applied through fixtures called emitters. Application is slow, so the water enters the soil before runoff or evaporation occurs; it goes directly to the plant’s root zone. The purpose of this handout is to supplement the free drip installation guides available online and at some local hardware stores. You should obtain one of these guides before you design your drip irrigation system.

Most of the soil in the City of San Luis Obispo has slow permeability. This means water does not penetrate very easily. For example, some of our local soil can accept water at a rate of only Ľ inch per hour! Water applied in moderate to large amounts, over relatively short periods of time, will almost certainly pool or run off and not reach the roots of the plants you are trying to irrigate. You can see why there is such a strong case for drip irrigation, or very low volume micro sprinklers, as opposed to hand watering in San Luis Obispo.

Every plant has different watering requirements, so you must keep a close watch while you determine an irrigation schedule. For example, shallow rooted annuals may require more frequent watering of shorter duration. Plants pick up water and minerals through tiny root structures called root hairs. These structures are sensitive to water loss, so they should not be allowed to completely dry out. Check the soil moisture by digging test holes in the area in question. If dry soil is invading the root zone, it’s time to apply more water. After a few test holes, you will probably have familiarized yourself with the state of your soil moisture, so you will be able to guess more accurately in the future. A general rule of thumb is when the first two to three inches of soil begin to dry out, it’s time to irrigate again; particularly with the least drought tolerant plants.

Choosing Your Emitters.

There are a variety of drip emitters on the market. Some emitters are adjustable and can easily be cleaned out; these are very desirable features Drip irrigation supplies. that could save you maintenance time and replacement costs. Check with you local hardware or irrigation supply stores before you choose which type of emitter to install. You may also contact the Utilities Conservation Office for information on the types of materials that are currently available.

Irrigation.

Most drip irrigation guides carry irrigation schedules that may be useful, but keep in mind that the schedules may need to be modified for use in San Luis Obispo. Some of our soils are quite shallow, or tend to limit root depth due to a high clay content. If your guide says to space two emitters at the base of a tree, and water seven hours at a time, twice per week, that may be excessive for our area. In shallow soils, or with shallow rooted plants, such a schedule will distribute water well past the root zone, where it will be wasted. Instead, check the literature to determine how much water your emitter delivers per hour, and irrigate only long enough to distribute water to your plant’s root zone.

In the case where root zones are shallow, try experimenting with more emitters that run for less time. For example, you can space emitters in a ring, under the outermost branches of the tree (Figure 1). Limit your duration so that each emitter distributes about one gallon, twice per week during the warmer seasons. This will place the water where you need it, without exceeding the appropriate root depth. With this modified schedule, you may be able to water some of your less thirsty plants only once per month; particularly if you incorporate a heavy surface mulch to discourage water loss through evaporation.

Figure 1
Drip irrigatin tubes.

Maintaining Your System.

Drip irrigation tends to require more maintenance than sprinkler irrigation, but if you choose the right system, you will be rewarded with lower water bills, and a healthy landscape. Clogged or broken emitters are the most common problems. As with sprinklers, a monthly check of the Drip irrigation emitter. system is recommended. Walk around while the system is running, to check for broken or leaky emitters, and to make any necessary adjustments. Regardless of the type of irrigation system you have, you should make sure you know how to operate your automatic sprinkler timer, if you own one. Check your handbook, or consult with your landscaper or the Utilities Conservation Office for help.

Surface Mulch

Thick surface mulch is a vital part of any drip irrigation system; its importance can not be overemphasized. Surface mulch can be anything from bark chips to grass trimmings. Placed over the emitters and the soil surface, it will prevent the sun from evaporating the water you apply, and you will need to apply much less water. For best results, apply surface mulch at least two inches thick; preferably thicker. Different textures are available to suite your landscape. Longer and finer textures are best for slopes, as they tend to interlock and resist moving downhill. An added benefit to surface mulch is weed control.

Types of mulch Drip irrigation around plants.

It is not uncommon for a thick surface mulch to preserve soil moisture for several weeks after the end of the rainy season. Thick surface mulch should be used over drip emitters only. In other systems, such as sprinklers and microsprays, it will act as a barrier; preventing water from reaching the soil.

Additional Information - More information is available on solving your Phone. water use problems. If you need to speak with someone, call the Utilities Conservation Office at 781-7217 or 781-7213.

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