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 plantís 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
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,
itís 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, itís time to irrigate again; particularly with the
least drought tolerant plants.
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
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
Most drip irrigation guides carry irrigation schedules that may be
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 plantís root zone.
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.
Maintaining Your System.
Drip irrigation tends to require more maintenance than sprinkler
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
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.
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
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.
More information is available on solving your
water use problems. If you need to speak with someone, call the
Utilities Conservation Office at 781-7217 or 781-7213.