Chapter 18
IrrIgatIon
by John Begeman
Knowing when and how to water plants is one of the most important aspects of gardening and
landscape plant maintenance; it is also one of the most complex. Many interacting factors
determine the frequency of application and the amount of water to be applied. Some of these
factors include: the plant's inherent water requirements based on species; the climate of the region
(maco climate) and the environment around the home (micro climate); the season of year; the type
of water delivery (irrigation) system; and the desire or necessity to conserve water.
A great portion of Arizona is either arid or semi-arid, and within these regions reside much of
the state's population. Tremendous and ever-increasing demands are being placed on our limited
water resources. As water for landscapes and gardens utilizes roughly 60% of the total water
consumed by residents, it behooves us all to make wise decisions about the use of this water for
irrigation purposes. This includes proper landscape planning, plant selection, efficient irrigation,
and wise water management practices.
2
Introduction
This unit is a brief introduction to irrigation principles
important to horticulturists. Proper design and
operation of irrigation systems requires experience,
science and art. Irrigation system design begins with
a landscape plan specifying plants suitable for the
available topography, soil, climate, and water. Plant
species adaptable to climate and soil conditions are
easier to irrigate and maintain. The following items are
necessary for design and operation of irrigation system
for landscapes.
— Plant water requirements (peak demand)
— Condition of the water and its supply
— Soil type(s), condition and topography
— Weather and climate information
— Microclimate concerns
— Irrigation scheduling constraints
Water Requirements
Irrigation water requirement is the quantity of water
which needs to be applied with the irrigation system.
The irrigation water requirement considers a plant’s
evapotranspiration (ET), irrigation losses, rain, and
leaching requirements. Typically only about 65 percent
of the total irrigation water delivered is available for
plant growth, the balance is lost to leaching or held too
tightly by soil particles to be absorbed by plant roots.
The portion of the precipitation available to plants
depends on the timing and amount.
Evapotranspiration (ET)
Weather and MicrocliMate
Evapotranspiration is the combination of evaporation
of water from the soil and transpiration from the
plants. Evapotranspiration is necessary for plant
Irrigation
3
growth (photosysthensis); it maintains a healthy plant
temperature and provides for the transportation of
nutrients to and through the plant. Evapotranspiration
requires energy. Energy comes from radiation and
advection. Radiation usually comes from direct sunlight,
and advection comes from heated air surrounding the
plant. In addition to the energy required for evaporation,
the air above the plant needs to be able to accept more
water. The drier (lower humidity) and hotter the air, the
more water the air can hold. If energy is being added to
the plant and no evaporation is taking place, the
temperature of the plant will increase.
ET can be estimated by mathematics equations that use
weather data (temperature solar radiation, humidity, rain
and wind) to determine available energy and humidity to
evaporate water. A potential ET can be adjusted to a
particular plant type, plant growth stage, plant
population, vigor, and stress.
The location of a plant in a landscape affects its ET
rate because of differences in available energy for
evaporation. The following lists show locations that
increase and decrease plant ET.
Increases available energy
— south or west exposures
— reflected sunlight from surfaces
— non-vegetative surroundings parking lots, streets
— proximity to desert
— exposure to dry hot winds or wind channeling
Decreases available energy
— north or east exposures
— shade by building
— shade by other plants
— sheltered from the wind
— locations in the center of largeirrigated or wet
areas
4
Plant Water Use
Plant species have different rates of ET based upon the
characteristics of the plants and available soil water.
Plant stomates are the evaporation surfaces on the
leaves. Plant leaves control transpiration by stomatal
closure. Leaves that reflect more of the sun's radiation
(gray or silver) usually transpire water at a lower rate
than green leaves. Plants that can tolerate higher leaf
temperatures evaporate water at a lower rate.
Low water use plant characteristics
— Low fertilizer requirements
— Slow growing plants
— Small or narrow leaves or leaves that roll-up
during high temperatures
— Leaf modifications (color, hairy, waxy, sunken
or reduced number of stomates)
— Small plant size
Drought tolerant plants are not necessarily low water
use plants and vice versa. For example, mesquite trees
are drought tolerant, but are high water users when
water is available. Drought tolerant plants go dormant
or near dormant when soil water is unavailable and then
become active when water is available. Some low water
use plants are not drought tolerant. Many plants
not normally considered low water use species become
water thrifty for survival when soil moisture is limited.
Some plants considered low water use species will use
water at a high rate if water is available and revert to low
water use when not available. Low water use plants don’t
conserve water if they are irrigated as high water use
plants.
Available soil water also affects the rate of transpiration
from plants. If soil moisture is limited, then
transpiration and plant growth decrease. If soil water
is abundant and not limiting plant growth (this does
not mean that it is being over-irrigated), turfgrasses
and many woody plants will maximize their water
Irrigation
5
use and maximize their growth. This may or may not
be desirable. For plants that need to survive and
reproduce from season to season, this allows them to
optimize a limited amount of natural rainfall. For
landscape plants under constant abundant irrigation,
this promotes succulence. Succulent growth does not
withstand traffic or wear (turf); is more susceptible
to disease and mechanical damage (wind); promotes
uncontrolled growth; encourages high water use;
decreases drought tolerance; and decreases tolerance to
heat and cold. Research has established that cool season
turfgrasses like perrenial ryegrass can survive at 80
percent of its maximum water use and not reduce turf
quality (80 percent of actual Evapotranspiration (ET)
rate). Bermudagrasses (not overseeded) can preform well
at 60 percent of its actual ET. However, caution should
be exercised when trying this over extended periods
because of the accumulation of soil salts
that will occur over time when irrigating with water
containing these salts. This same reduction in applied
water on ornamental plants and its effects has not been
examined. Generally speaking, the higher the aesthetic
expectations are from a landscape and the amount of
"abuse" expected, more water is required to meet these
requirements.
Other factors that affect plant water use are soil fertility,
turf mowing height and frequency. Fertilizer applications
that stimulate growth increase plant water use in turf,
ornamentals, fruits and vegetables. Pruning of landscape
plants also promotes growth that results in greater water
use. High, frequent mowing of turfgrass increases water
use by providing more leaf surface
for transpiration. However, this type of mowing also
increases rooting depth , thus making turfgrass more
drought tolerant.
Evaporation from open water surfaces is about 1.25
to 1.5 times more than from a well irrigated turf area.
There are no leaves and stomates to limit evaporation
6
from an open water surface. Natural and manmade
lakes can also lose water through leakage and deep
percolation.
Tips for minimizing plant water use:
1. Select native and low water use non-native
plants whenever possible.
2. Select smaller plants over larger plants
whenever possible.
3. Use as much hardscape or surface mulched
areas as possible.
4. Reduce fertilizer use to the lowest level possible
while maintaining acceptable plant health and
aesthetics.
5. Use surface mulches around plants and in bare
soil areas.
6. Avoiding excessive irrigations.
7. Water trees, shrubs, ground covers, and
herbaceous plants to their potential rooting
depth.
8. Zone irrigation systems, separating plant
materials by water use, exposure, topography
and soil type.
9. Increase mowing height of lawns to allow plants
to develop deeper root systems.
10. Keep the lawn mower blade sharp. Sharp mower
blades make cleaner cuts that cause less water
loss than cuts from dull mower blades.
11. Control all weeds. Weeds use water that would
otherwise be available for desirable plants.
12. Cull plants that are growing poorly. Don't waste
water caring for marginal or undesirable plants.
13. Apply wetting agents to hydrophobic (water
repelling) soils.
14. Match nozzle and emitter to deliver the same
Irrigation
7
gallonage output.
15. Keep sprinkler heads and drip emitters clean to
ensure uniform water distribution.
Irrigation losses
Irrigation losses consist of spray drift and evaporation
losses, deep percolation due to over-irrigation,
uniformity losses, required salt leaching and runoff.
Spray and drift losses range from 10 to 30 percent. The
losses depend on time of application, wind, sprinkler
type and sprinkler water pressure. High pressures
break up the water into small drops that creates more
evaporation and drift. Deep percolation due to irrigation
non -uniformity and overestimates of plants' needs
range from 10 to 35 percent. Uniformity losses include
uniformity of application, as well as uniformity of soil
infiltration. Once an irrigation system is installed, it will
have a characteristic uniformity of application (how
evenly water is applied to the site), which is dependent
on:
— how well the irrigation components were
engineered.
— how the system was designed.
— how the system was installed.
— how the system was maintained.
Irrigation components from major manufacturers will
give reasonable uniformities when the correct nozzles
are chosen, water pressure is regulated with an
appropriate design and maintenance schedule.
It would be advisable that a new system should be
designed or approved by a certified irrigation designer.
After installation, the system should be audited by a
certified auditor or someone trained to perform audits,
with a minimum acceptable, uniformity established
prior to the installation and agreed upon by the client,
designer and contractor. Once a system has been
installed with a guaranteed uniformity and audited,
the maintenance contractor must be aware that any
changes in head spacing, number of heads, nozzle sizes,
8
head manufacturer or model, pipe sizing and operating
pressure will decrease uniformity and increase water
use. The maintenance contractor (when applicable)
should be responsible for regular replacement of worn
nozzles and emitters, checking heads and emitters
for proper operation, clearing and cleaning heads and
emitters of blockage and debris, replacement or
maintenance of non-operating heads and emitters,
fixing leaks and breaks, regular maintenance of
irrigation components and monthly irrigation
scheduling.
Just because a system applies water uniformly does not
mean plants receive water uniformly. Problems
associated with systems applying water more rapidly
than soils can absorb; 2) slopes and landscape mounds;
and 3) compacted soils all decrease the time available
for infiltration to take place, leading to runoff and
puddling in low spots. This requires the application of
more total water than is needed to cure dry areas.
Correcting irrigation losses from spray drift, wind and
evaporation:
1. Use low volume drip or micro-spray irrigation.
2. Use a pressure regulator on the system if
pressure is too high or booster pumps if too low.
3. Use low angle nozzles in windy locations.
4. Irrigate during early morning hours when winds
and evaporation are typically lower.
5. Design spacing of heads to compensate for
windy locations.
6. Select heads and nozzles that provide a
predominance large water droplet sizes rather
than fine sprays.
Correcting losses from deep percolation:
1. Calculate irrigation run times to wet the
observed root zone, no more.
2. Zone irrigation systems to types of plant
Irrigation
9
material and their characteristic rooting depths
3. Know your water quality so the proper
leachingfraction can be included in an
irrigation.
Correcting uniformity losses include:
1. Correct all obvious irrigation distribution
problems, e.g., sunken heads blocked heads,
non-rotating or plugged heads, tilted heads,
replace worn or improperly sized nozzles and
spray angles replace substituted heads for
design-specified heads, check "As-Built"
irrigation design for field compliance, and
review any designs done by a non-certified
designer with a certified designer.
2. Do a complete irrigation audit, recording catch
can values corresponding to sprinkler head
locations.
Correcting runoff losses:
1. Aerate slopes and compacted soils.
2. Construct reservoirs around landscape plants
irrigated with bubblers.
3. Select drip emitters with a lower G.P.H.
(gallons per hour) output.
4. Schedule irrigations with several stop/start
cycles to increase infiltration time.
5. Redesign slopes and mounds to eliminate turf
and concentrate turf on flat areas.
6. Place a landscape "buffer area" designed with
drip irrigation between turf and parking lots,
sidewalks, driveways and hardscapes.
7. Not placing overhead irrigation on median
strips or planter areas.
Water Supply
10
Most water used in horticultural irrigation is supplied by
municipalities or water districts. These agencies can
provide information on the cost, quality, quantity and
pressure of the water they supply.
Effluent
Other sources of irrigation water may be treated
effluent or waste water, wells, and surface water such
as streams, rivers, reservoirs, and lakes. Effluent or
waste water may be an available, economical source
of irrigation water. Water for irrigation can be lower
in quality, requiring less treatment than municipal
water. Use of effluent for irrigation can have both
environmental and economical benefits.
Usingeffluenthasthefollowingpotentialbenefits:
— Conserves higher quality water supplies.
— Lower cost than water treated for drinking.
— Plants remove nutrients, such as nitrate, in
effluent water which improves water quality and
reduces plant fertilizer requirements.
Effluent water reuse for irrigation has the following
limitations:
— Health concerns (protozoans, fungi, bacteria and
viruses).
— Quality control because of annual and seasonal
changes in effluent quality.
— Irrigation demand may be inconstant with
effluent water supply.
— Irrigation system design and maintenance
considerations.
— Water quality and potential toxic elements build
up in the soil.
— Higher salt concentrations.
Water Quality
Irrigation
11
If the proposed irrigation water supply has not been
previously used for irrigation or you are uncertain about
the water, have the irrigation water quality determined by
a chemical analysis. Water quality analysis can be
obtained through private soil and water testing firms.
Have the analysis interpreted by a professional.
Water testing
A water-quality analysis will indicate concentrations, in
parts per million (ppm) or milligrams per liter (mg/1),
of most of the following. Effluent water may also
contain toxic amounts of boron, chloride, copper,
nickle, zinc, cadmium or aluminum:
Sodium (Na)
Potassium (K)
Calcium (CS)
Magnesium (Mg)
Carbonate (CO3)
Phosphorus (P)
Sulfate (SO4)
Nitrate (NO3)
Total dissolved salts (TDS)
Electrical conductivity (EC)
Bicarbonate (HC03) Sodium absorption ratio (SAR)
Chloride(CI)
pH
Boron (B)
Private laboratory fees will range from $25 to $150
per sample. Generally an interpretation of the results is
provided together with recommendations.
You may request additional tests for heavy metals, such
as aluminum and manganese and total suspended solids
(TSS) to assist you in designing appropriate filtration
systems.
1. Total Dissolved Salts (TDS)
Applying salt-laden- irrigation water restricts root
absorption of water and reduces water availability as
soil water becomes limited. The resulting high soil
salinity makes it increasingly difficult for the plant’s
roots to extract water. More frequent and deeper
irrigations are required to leach salts below the root
zone.
If the irrigation water has less than 640 ppm (1
millimhos per centimeter) total dissolved salts (TDS), it
12
will be suitable for nearly all applications. Under most
circumstances, water with a total salts concentration of
more than 1,920 ppm (3 mmhos/cm) is unacceptable for
irrigation of most garden and landscape plants. When
using water of marginal quality with salts in the range
of 640 ppm to 1,920 ppm, use the management
practices listed at the end of the water supply section.
2. Salinity
Plants remove much water from the soil but only a small
amount of soluble salt. Evaporation also removes water,
but no salt. Salts contained in irrigation water
can therefore be removed effectively only by applying
enough excess water to leach them downward, out of
the root zone where they can accumulate or into the
underground drainage system. Indicated “leaching
requirements” give the amount of water (%), in excess
of plant requirements, which must be applied and
drained down through the root zone in order to control
salt accumulation. Plants vary widely in their salt
tolerance, as indicated in table (1).
3. Sodium
Sodium often times can appear in relatively high
concentrations in arid soils. High concentrations
of sodium in the soil or applied to the soil through
irrigation water result in the soil becoming laden with
sodium. The soil structure is then destroyed, clogging
soil pores and reducing permeability. For this reason do
not use softened water for irrigation. Water softening
replaces calcium and magnesium with sodium. Some
residences have their entire interior plumbing on
softened water. Hose bibs on exterior walls of homes
may also be on softened water.
The sodium absorption ratio (SAR) is the term used to
express the level of sodium in irrigation water.
Assuming adequate drainage, you should not exceed an
SAR of 18 in irrigation water for turfgrass applications.
For garden and landscape plants, maintain an SAR
below 10.
4. Bicarbonate
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13
Table1.PlanTToleranceTosalinTi yandleachingrequirem enTs.
Plants
EC mmhos/
cm irrigation
water
EC mmhos/
cm soil water
Leaching
requirement
Vegetables
beeTs
3.5
5.3
11
sPinach
2.5
3.8
10
TomaTo
1.8
2.7
8
broccoli
1.8
2.7
8
cabbage
1.1
1.7
6
PoTaTo
1.1
1.7
6
corn
6
sw eTPoTaTo
1.1
6
leTTuce
1.1
1.7
6
bellPePPer
1.1
1.7
7
onion
0.9
1.3
8
carr oT
0.7
1.0
6
beans
0.7
1.0
7
aPPleP/ ear
1.1
1.7
7
ParicoT/Peach
1.1
1.7
7
rasPberry
0.8
1.8
8
sTrwa ber y
0.7
1.0
7
berm uda
5.0
7.6
15
Tallf escue
3.5
5.3
11
Pereniarl ye
3.5
5.3
11
annuralye
3.5
5.3
11
Fruit
Turf
14
Water that is high in bicarbonate may aggravate a
sodium problem. The residual sodium carbonate
(RSC) reflects the presence of excess carbonate and
bicarbonate.
AnInR
ouwaliintydiRcaetpeosrw
teS
rpCreotfin1g.2a5Woartb
erelQ
t ater that is safe
for irrigation. A value between 1.25 and 2.50 represents
Total dissolved salts (Tds)/
salinity
remarks
0-640PM=0-1MMHO/CM
SA FEFORI RIGATION
640-1920PM =1-3MMHO/CM
MARGINALQUALITYWATER
1920+=3+MMHO/CM
UNSAFEFORMOSTPLANTS
sodium (sar)
0-10
SA FEFORGARDENSANDLANDSCAPES
0-18
SAFE FORTURFGRASS
bicarbonate (rsc)
0-1.25
SA FEFORI RIGATION
1.25-2.50
MARGINALWATERQUALITY
2.50+
UNSUITABLEFORIRRIGATION
marginal water quality. Water with an RSC greater than
2.50 generally is considered unsuitable for irrigation.
5. Boron Hazard
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15
A small amount of boron is necessary for plant growth.
Most Arizona soils have adequate boron for crops, and
most surface waters carry it. Some wells and saline
water contain toxic levels, and should be avoided.
Management practices for poor quality irrigation
water
Once you have determined the quality of the
irrigation water, there is very little that can be done
to inexpensively improve the water quality. However
these management practices can be followed to improve
chances for maintaining plant health.
— Schedule irrigations beyond plant use to
increase soil leaching.
-— Improve soil drainage characteristics to enhance
leaching.
— Use plants more tolerant to water quality and
site conditions.
-— Blend poor quality water with good quality
water.
— Apply water high in salts through drip or
subsurface irrigation. Salty water is more
damaging when applied to the foliage.
Irrigation System Selection
Sprinkler, drip, and surface are three basic irrigation
system types that can be used in horticulture
applications. Each system type has many variations
adapted for specific conditions.
Sprinklers
Sprinkler systems are commonly used for turf
applications. Selection of sprinkler type depends on size
and shape of area being irrigated, and the flow rate and
pressure of the water supply.
Rotating Sprinklers
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Full and part circle rotating sprinklers are used to irrigate
large areas. These sprinklers can have single or multiple
nozzles, gears, cam or impact driven, spacing from 35 to
115 ft, operating pressures from 40 to 100 psi, and flow
rates from 6 to 65 gpm. Some rotating sprinklers have
built-in valves (valve in head) and/or pressure regulators.
Depending on nozzle size, pressure and sprinkler
spacing, average application rates vary between 0.25 and
1.0 inch/hour. The application uniformity of rotating
sprinklers depends on sprinkler geometry, angle of
trajectory, wind, nozzle size, pressure and sprinkler
spacing. Each sprinkler has a specific application, design
and operating requirement. Consult an irrigation
contractor or supplier for specific information on the
design of irrigation systems. Improper design and
installation of a sprinkler system will result in poor
uniformity and water waste. Water pressures higher than
recommended tend to make small water drop size which
are subject to evaporation and drift in wind conditions.
Low water pressures decrease the radius of throw and do
not break up the water
stream properly, causing poor uniformity of application.
Sprinkler spacings too close or too far apart decreases
application uniformity.
Rotating heads are usually used for large turf areas
such as golf courses, parks, commercial or large
residential landscapes. Their precision usually results
in high uniformities (up to 90 percent uniformity of
application) when designed and installed properly.
Low precipitation heads can be used on slopes or other
problem areas with less chance of runoff.
Fixed Spray Sprinklers
Small turf areas are often watered by pop-up or fixed
spray heads. Spray heads can have full, part circle or
rectangular patterns, with radiuses from 4 to 22 feet,
several angles of spray trajectory, application rates
ranging from less than 1 to over 2 inches per hour. The
application uniformity of sprays are very dependent upon
spacing, nozzles pressures, sprinkler orientation and
nozzles size. Generally spray heads should be operated at
low pressures 15 to 50 psi. Higher pressures cause
excessive drift, evaporation and poor application
uniformity. Many residential landscapes are irrigated
Irrigation
17
with spray nozzles without a pressure regulator
resulting in poor uniformities. The high application
rates of spray nozzels needs to be considered in
irrigation scheduling and application to prevent runoff.
Pop-up spray irrigation systems typically have the
poorest uniformities, possibly reaching a maximum
of 70 percent uniformity of application. Their high
precipitation rates make them a problem on many
landscapes with slopes, mounds, compaction or heavy
soils. Pop-ups vary from 2-inch heights for warmseason grasses and others mowed at 1-1/2 inch or lower,
up to 18-inch for shrub or planter areas.
Drip and Micro-Sprinklers
Micro sprinklers are a cross between spray nozzles and
drip irrigation. These sprinklers have low flow rates,
low application rates, small radiuses and operate with
low pressures. Sprinkler flow rates range from 0.1
to .07 gpm, average application rates from 0.2 to 0.4
inches per hour, wetted radiuses from 4 to 12 ft and
operating pressures from 10 to 25 psi. They are very
well suited for small ornamental plantings and single
trees or shrubs. Micro sprinklers require filtered and
pressure regulated water.
Drip
Drip or micro irrigation applies water to the soil at point
locations at low controlled flow rates. Drip emitters
discharge from .5 to 2 gallons per hour. Many emitters
are pressure compensating, applying a nearly constant
application rate over a wide range of pressures. Emitters
are installed by individual plants or grouping of plants.
All drip irrigation systems should include a filter and
pressure regulator.
Drip Tubing
Drip tubing is another form of drip irrigation in
which water is emitted at equally spaced points (6 to
60 inches) along a tube. There are semi-rigid tubing
with emitters built in the tubing. These emitters can
be pressure compensating. The tubing is similar to
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polyethylene irrigation tubing. Bi-Wall drip irrigation
tubing has a main chamber (tube) to supply water to an
outside secondary distribution chamber with drip holes
regularly spaced. Bi-Wall tubing is thin walled and is
less expensive and durable than the semi-rigid drip
irrigation tubing. Irrigation tubing discharge is
expressed in gpm per 100 ft of tubing or in gallon per
hour per emitter. There is also porous drip irrigation
tubing that allows water to seep out along the entire
length of the tube. Depending on the drip irrigation
tubing type, operating pressures are from 5 to 20 psi.
Drip irrigation tubing can either be laid on top of the
soil or buried in the soil. Buried drip tubing is being
sold to irrigate turf.
Bubblers
Bubblers are similar to drip emitters except that they
have a much higher flow rate. The flow rate of bubblers
is adjustable from 2 to 6 gpm, resulting in application
rates much higher than soil intake rates. Bubblers
essentially flood a small area and the water continues to
infiltrate into the soil after the bubbler has been shutoff.
Bubblers are only applicable in areas where small basins
can be constructed to contain the water and where the
soil is surface is level.
Surface or Flood Irrigation
Surface or flood irrigation systems can be used in a
few horticulture situations. Surface irrigation generally
applies deeper irrigation and requires higher flow
rates for a shorter period of time than sprinkler or
trickle. Leveled and diked turf areas can be irrigated
by flooding if the soil infiltration rate is slow enough to
allow the water to flow over the entire area. Landscapes
and gardens are sometimes irrigated with furrow or
diked irrigation. In surface irrigation the soil is the
distributing and infiltration system and requires careful
design for efficient irrigation. Surface irrigation is
limited by the slope of the area.
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19
All types of Irrigation methods and systems have
both advantages and disadvantages that need to be
considered in each specific application and design.
Irrigation System Design
The main objective of an irrigation system is to supply
adequate and timely water to plants. This objective
should be considered when designing an irrigation
system. Two considerations that help achieve this
objective are irrigation zones and irrigation system
layout. The hydraulic engineering of the irrigation
system is secondary to a good system layout. Proper
hydraulic engineering is of little value if the system has
not been properly zoned and planned.
Irrigation Zones
Irrigation zones should be selected based upon the plant’s
irrigation water requirement and sized according to
available water supply. Zone irrigation systems should
consider the following:
1) Plants from deep rooted zone & low water use
plants separate from high water use. Separate
and distinct watering requirements for turf,
drought tolerant vs. non drought tolerant
landscape plants and herbaceous garden plants
(vegetables and flowers).
2) Exposure to sun and wind.
3) Different soil types.
Figure 1: Typical plant root zones
Plant
canopy
Turf, vegetables,
ground cover,
bedding plants
20
shrubs
18"-36"
Trees
4) Different depths of rooting and thus different
depths of wetting for trees (18-36 in.), shrubs
(12-24 in.), herbaceous plants and turf (6 -12
in.) (Figure 1).
Turf areas are better suited to irrigation by sprinklers,
while landscape plants (especially in heavy soils with
low water infiltration rates) are better irrigated with
low-flow drip or micro-spray irrigation.
Some zones may require daily irrigation; others require
weekly irrigation; and still others may reqire only bimonthly or monthly irrigation. Some controllers do not
have the capability of separating irrigation frequency for
different zones. The more complicated electronic
controllers have these programming capabilities.
These controllers are more expensive and require more
effort to program and understand than the simpler
controllers. In some situations it is less expensive and
more practical to have two or more separate, simpler
controllers to accommodate the irrigation of different
zones.
Irrigation System Layout
Controller (time clock) and valves boxes should be
located in accessible locations. Controllers should be in a
protected area away from the rain and direct sunlight
unless they are in a protective enclosure. Before laying
out irrigation lines, sprinklers or emitters a scale drawing
should be made showing the entire property with the
location of all plants indicated.
Sprinklers should be selected which fit the size of the
area being watered. It is usually best to begin in the
corners where a sprinkler is required when determining
sprinkler location. A head-to-head sprinkler spacing
usually applies water quite uniformly. Head-to-head
coverage implies that water from one head -reaches the
adjacent head. Locate sprinklers based on the mature
landscape, considering size and location of any shrubs.
When laying out a drip system, begin by locating the
emitters associated with individual plants or plant
groupings. Spacing of emitters is based on the ultimate
Irrigation
21
spread of the root system (root zone) and the soil type.
Refer to the section on Water Scheduling for details
on emitter placement and water application. After
determining the number, output and placement of
emitters, water supply lines (laterals) may be located,
noting the length of tubing and connectors needed
to bring the water from the source (hose bib) to the
emitters.
Complicated and large irrigation systems (spray
or drip), should be designed by professionals who
select pipe sizes based upon friction losses and water
velocities. Residential drip systems using less than
250 gallons per hour, with laterals less than 200 feet in
length, using pressure-compensating emitters, and using a
25 or 30 p.s.i. pressure regulator need no technical design
considerations. Residential landscapes with only a few
sprinklers on each zone can use 1 or 3/4-inch
pipe through the entire system. The wire to control
the valves should be sized considering the amperage
requirement of the valve and the length of run.
With the help of information supplied by many
irrigation supply retailers, drip systems can be
sucessfully designed and installed by the home
gardener. One of the most important aspects of the
design is to determine the system=s capacity. Most
home systems use less water than the hose bib is
capable of delivering. If, however, the system needs
more water than the hose bib can deliver at one time,
it can be divided into additional zones as necessary. To
determine the hose bib capacity, run the water full
force into a measured bucket. If, for example, a three
gallon bucket takes 30 seconds to fill, then the capacity
is 6 gallons a minute or 360 (6 gal. x 60 min.) gallons
per hour. Total the gallonage output of the emitters in
22
the system. You can increase the capacity of the system
Figure 2: Basic components of a drip system
(not to scale)
house
controller
galvanized "T"
backflow preventer
galvanized 90° elbow
galvanized union
galvanized pipe nipples
Valve box
remote control valve
y filter
Pressure regulator
end cap
Transfer barb
"spaghetti" tubing
emitter
"Poly" (.580 Pe tubing)
uf wire
gravel for drainage
by reducing emitter sizes and running the system
longer. To maintain a safe margin, the system should
be designed so that it doesn't use more than 75% of the
bib's capacity.
Irrigation System Components (figure 2)
The following are basic components of an irrigation
system.
— Water source (municipal, effluent, well, etc.).
— Meter (may be required by water supplier).
— Backflow prevention and vacuum breaker
device protect water supply. This is required by
law and is also a good safety feature.
— Valves (manual or automatic) and wire.
— Pressure regulator (drip irrigation).
— Filtration system (drip irrigation).
— Controller and related hardware if using
automatic valves. Most automatic valves
are electric and require wires connecting the
Irrigation
23
controller and valves.
— Distribution pipe and pipe fittings.
— Sprinklers, drip emitters, drip tubing or
bubblers.
A landscape should be designed considering the
irrigation system, and the irrigation system should be
designed considering the landscape plan. Automatic
irrigation systems should be zoned considering irrigation
type (drip or sprinkler), plant types, exposure (north or
south) and soils. The factors that influence plant water
use should be considered in determining irrigation
zones. An irrigation zone is the area irrigated by
opening a single valve. In selecting an irrigation system,
a combination of several system types can
be used but not in the same zone. Each zone should
Pop-up spray
Valve
bubbler
impact
head
spider spray
Figure 3: Mixed heads
have only one type of nozzle or emitter. Spray nozzles
should not be mixed with impact (rotating) sprinklers,
bubblers, spider sprayer or other dissimilar types because
of their varying application rates (figure 3). All
sprinklers in a zone should have matched application
rates. For example, a half circle sprinkler should have
half the flow rate as a full circle sprinkler.
Drip emitter in a zone may or may not have matched
flow rates. If zones are determined on the basis of
rooting depth, such as if all trees are on the same zone,
then emitters on that zone should all have the same flow
rate or gallonage output. However, if zones are
detemined on drought tolerance; and a mixture of plants
24
with varying rooting depths such as trees, shrubs, and
ground covers are used, then emitter output can be
altered to reflect this variation. For example, trees
may be placed on higher gallonage output emitters
than shrubs, and shrubs on higher output emitters than
ground covers. In this way, although the watering
duration may be the same, the depth of wetting will be
determined by the gallonage output.
The water requirements and pressure of irrigation zones
(spray or drip) should by less than the available water
supply and pressure.
1. Water source
See the section on Water Testing.
2. Water Meter
Some water suppliers require a water meter to be
installed. Residential water meters are normally 5/8
or 3/4 inch. Flows through residential water meters
should be limited to about 15 gpm; otherwise there is
excessive pressure loss through the meter and other
water fittings and valves. Private and commercial
recreation areas with large irrigated areas require larger
meters to supply the necessary flow of water without
high pressure losses. Where meters are installed on the
molded plastic poppets
Test
cocks
gate valve
Figure 4: Pressure vacuum breaker
Irrigation
25
irrigation system, they can provide a management tool
to help determine irrigation scheduling and evaluate
watering efficeincy.
3. Backflow Prevention and Vacuum Breaker
Devices
Backflow prevention and vacuum breakers are
required to protect drinking water supply (figure 4).
Contaminated irrigation water can enter a municipal
system if the municipal system loses pressure and
there are no backflow prevention devices. The pressure
loss across a back-flow prevention device needs to be
considered in the design of an irrigation system. A 3/4inch backflow prevention device may have a 5 to 10 psi
pressure drop at 10 gpm.
Many communities require a specific backflow
prevention device for a specific location or use.
Backflow occurs through either back siphonage
(temporary lower pressure occurring upstream from the
point of contamination) or back pressure (temporary
higher pressure occurring downstream from the point of
contamination). Either can result in contaminated water
entering a potable water delivery system.
4. BoosterPumporPressureRegulators
The pressure of the water supply may not be the pressure
required by the irrigation system. Municipal water
system pressure may be too high for drip and spray
irrigation systems. To reduce the system pressure,
pressure regulators can be used. Municipal water
system pressure can to be too low for an irrigation
system using large rotating sprinklers. To increase the
pressure, a booster pump can be used.
5. Filtration System
Drip emitters and drip tubing have small orifices which,
without filtered water, may clog. Filters are a good
precaution, even for high-quality irrigation water, when
using drip irrigation.
26
6. Chemigation Equipment
Chemigation can be a cost-effective way to apply
chemicals such as pesticides and fertilizers. Safety and
backflow protection devices are essential for
chemigation. Most chemical injector systems inject the
chemicals at a higher pressure than the irrigation
system’s pressure. This could potentially contaminate
a pressurized municipal water system. The uniformity of
the irrigation application will also be the uniformity of
chemical application. High uniformity is a must. Excess
deep percolation during an irrigation in which
chemigation is being used will result in chemical
movement past the root zone and possible ground water
contamination.
7. ValvesandWire
Irrigation systems require valves to control the water
being applied. Most automatic valves are electric
(24 Volt) and require wires connecting the controller
and valves. Wires must be sized to account for the
length of the wire and the current requirement of the
valve. Undersized wires result in a voltage drop and
inadequate voltage at the valve.
Most valves will have a "manual bleed valve" or
"bleed screw" located on the valve body or on top of
solenoid
flow control
manual bleed valve
bonnet
diaphragm
Figure 5: Typical remote control valve
Irrigation
27
the flow control handle. The bleed screw allows for the
opening of the valve (turning on the sprinklers) without
electrically actuating the valve. This is an aid when
troubleshooting a system (figure 5). Some valves have
a "flow control" handle. This handle controls the rate of
water flow through the valve and is especially useful for
drip irrigation systems and low-pressure sprinklers.
All electric valves have a solenoid. The valve solenoid is
an electromagnet that, when electrically operated, allows
water in the line to push a diaphragm in the valve open
which allows water to flow through the system. Some
low-pressure drip irrigation systems may require valves
that open under very low pressures to operate
effectively.
8. Irrigation Controllers
An irrigation controller can control pumps and electric
solenoid valves in an irrigation system. Some irrigation
controllers can be coupled with electronic weather
stations or soil moisture sensors, such as tensiometers,
to assist in efficient irrigation scheduling.
9. Distribution PipeandPipeFitting
Distribution piping includes the mainline pipes and
the lateral pipes downstream of the valves. In sprinkler
irrigation systems polyvinyl chlorine (PVC) pipe is
usually used. This pipe is usually white or blue and is
semi-rigid. Irrigation tubing is used for drip irrigation.
This pipe is made of polyethylene (PE) and is black and
flexible. Irrigation tubing (PE) is constructed to resist
breakdown by sunlight and can be laid on top of the
ground.
10. Sprinklers, Drip Emitters, Drip Tubing or
Bubblers
28
Sprinklers, drip emitters, drip tubing and bubblers are
used to apply the water to the soil. Water application
devices should be selected to apply the water as
uniformly as possible to the area being irrigated.
Irrigation System Installation
Proper installation of the irrigation system is required
for efficient irrigation and water conservation. The
following are general guidelines for irrigation system
installation.
— Call utility companies (telephone, cable TV,
electric, gas, and water) for blue stake service
to mark all utilities in the construction area
before digging or trenching.
— Use drawings and specifications to mark
locations of valve boxes, pipe, sprinklers and
drip emitters before installation. Mark locations
with flags or stakes. This visual inspection of
the system allows for minor adjustment in the
system layout before installation.
— If the irrigation system is being installed in
phases, plan ahead so the landscape does not
need to be disturbed for installation of pipe and
wire required later.
— Installed pipe should be deep enough so that
ground frost, soil aeration and tillage operations
can’t disturb the pipe. For medium to large
irrigation projects, a mechanical trenching
machine may be rented to reduce labor. The
pipe and wire should be bedded in soil without
large rocks. Most pipe used in irrigation
systems is PVC which requires both threaded
and glued connections. Two layers of teflon
tape should be used on the male end of PVC
threaded connections. Excess teflon tape and
over tightening threaded connections can cause
excessive stress on joints. One turn past hand
tight in general is sufficient. Flush the pipe line
before installing sprinklers.
Irrigation
29
finish
grade
Pop-up sprinkler
galvanized
riser
PVc
lateral
PVc tee
stress point
Rigid connections are more likely to
break under stress.
finish grade
head
vertical
3/4" street ells
3/4" sched 80 nipple
(length as required)
3/4" street ell
PVc tee
— Wire conections must be make between each
valve solenoid and the irrigation controller (time
clock). Wire splices must be waterproofed. Wire
nuts and plastic tape are not waterproofing.
Waterproof wire connection kits can be
purchased. Make all wire splices in valve boxes.
Use white wire as the common and colored
wires for “hot” wires. Valves should be installed
in valve boxes which allow access to the valves
for repair or replacement.
PVc lateral line
Installed swing joint showing all parts.
Figure 6: Two connections
Rotating and spray sprinklers should be
attached with appropriated size swing or
flexible connections (figure 6). These types
of connections provide protection to the pipe
line and allow adjusting the height and level
of the sprinkler. Install part circle sprinklers so
that they are irrigating the proper area.
Adjustment of operating sprinklers should be
made immediately after installation of irrigation
system.
— Trenches should be back-filled and watered,
then back-filled again. This reduces settlement
of soil in the trench below the grade of the
landscape.
— During and after installation, drawings should
be made with the true location of all irrigation
lines (as-built plans) to assist in troubleshooting, maintenance, repair and future
modifications.
Drip irrigation systems are sometimes installed
on the surface of the ground. When installing
drip emitters in the tubing remember that the
30
irrigation tubing is longer on a hot afternoon
than in the cool mornings During installation
of irrigation tubing allow enough slack in the
tubing to account for temperature induced
tubing length differences.
Irrigation System Maintenance
Proper maintenance of an irrigation system is required
to insure efficient uniform irrigations. Ensuring that the
sprinklers and emitters are working properly is a major
clogged nozzle
clogged nozzle
Figure 7: Distorted patterns of spray nozzles
part of irrigation system maintenance. The following
items help keep sprinklers operating properly.
— Keep heads properly aligned, leveled, and
rotating.
— Clean plugged sprinklers, emitters and filters
when needed (figure 7).
— Replace broken sprinklers, worn nozzles and
emitters with appropriate parts to maintain
matched application rates and uniformity.
— Keep grass and plants away from sprinklers so
spray patterns are not disturbed by them. Raise
sunken heads.
— After evaluation move, add or remove sprinklers
and emitters to make a more uniform application
of water.
Irrigation
31
Visual inspection of the landscape provides a good
indicator of irrigation problems. Both stressed (hot
spots) and over irrigated (soggy spots) areas indicate
irrigation problems. If the irrigation system is operating
improperly the following items should be checked.
1. Water supply — Check to see if all valves are
opening and the system has proper pressure.
2. Controller and controller programming -—
Check the controller to make sure it is operating
and programmed properly.
3. Field wiring — Check to see if the automatic
valves are receiving the proper voltage and
current, check for shorts in the wiring.
4. Valves — Use the controller to manually operate
the valves through a cycle to make sure they
are operating properly. Adjust the flow control
stems on the valves if needed.
5. Sprinkler heads — Check for plugged, blocked
or broken heads. Make sure the sprinkler is
rotating properly.
6. Pipe and fittings — Check for broken or
plugged pipes and leaks.
Irrigation System Evaluation
Visual inspection of irrigation system
Visually look for signs of over or under irrigation and
for causes of problems. Turn on the sprinklers and look
for problems which are possible causes of dry or
soggy spots. Items to look for are plugged sprinklers or
emitters, misaligned or tipped sprinklers, improperly
operating sprinklers, improperly adjusted sprinklers,
sunken sprinklers, or imporperly spaced sprinklers or
emitters.
Determining Application Rates
32
Figure 8: Measuring water levels in containers placed
in a sprinkler's spray pattern helps determine how
much water is being applied.
Spray irrigation is primarily used for the irrigation
of turfgrass areas. Recommended application rates
are based on inches per application or inches per
week. For this reason, the application rate of an
overhead spray system must be determined for proper
irrigation scheduling. The easiest way to determine the
application rate in inches is to use the catch can test
(figure 8). A number of straight sided cans (canned
vegetables, tuna, etc.) should be placed randomly in
the lawn area. The greater the number of cans, the
greater the test accuracy. Usually 5 or 6 cans per 500
square feet of lawn area is adequate. After running the
sprinklers for a predetermined length of time, measure
the depth of water in each can using a ruler.
Determine the average application rate by adding the
inches, or fraction of inches, in each can and divide by
the number of cans. If this average is more than the
recommended rate of application in inches, the length
of watering should be reduced accordingly. If
the average is less than the recommended rate then the
length of watering should be increased accordingly.
In the case of drip irrigation, application rates cannot be
measured in inches. To determine the run time of drip
irrigation systems, the depth of wetting must be
determined and adjusted based on the rooting depth of
the plants being irrigated. See Irrigation Scheduling.
Irrigation Scheduling
Water scheduling is the process of determining how
to apply water to plants. It includes knowing where to
apply the water, how much water to apply, and how
frequently it should be applied.
Soil Type and Plant Material
Irrigation
33
The first consideration in determining a water schedule
for garden and landscape plants is the soil type. Soil
can range from a sand to a heavy clay. Sand is easy
soil:
emitter:
Time:
sand
1 gph 1 gph
1 hour
loam
clay
2 gph
6 hours
6 hours
Figure 9: Wetting patterns by a single drip emitter on sand,
loam, and clay soils
to dig, but does not hold water well. Water penetrates
deeply, but not very wide. Clay soils are difficult to dig,
especially when dry, but hold water very well. These
soils will dry more than sand and can crack. Soaker
hoses and drip emitters need to be spaced more closely
on sand than on clay (figure 9).
handle
2-3'
marks at 6"
intervals
Point
Figure 9b: A soil probe made from 1/4-to3/8" metal rod
34
Compacted soils or shallow soils over caliche or bedrock
can also cause problems. Water, air, and roots cannot
penetrate compacted soils very well. Compacted soils
should be tilled. Shallow soils (less than two feet deep)
cannot hold very much water and are easy to flood. You
should water a shallow soil more frequently than a deep
soil. Conduct a soil probe test to learn how deep and
wide your soil will wet. If possible, water
from a single outlet (a single bubbler, soaker hose, or
drip emitter) for a set length of time, say thirty minutes
for the bubbler up to two hours for the soaker hose
or drip emitter. Wait a short while after you turn the
water off, then push a soil probe (Figure 9b) into the
wet soil at several places. A soil probe is a 1/4 to 3/8
inch diameter metal rod, 2 to 3 feet long, with one
end sharpened to a point, and the other bent to form
a handle. The probe should easily push through the wet
soil and stop when it reaches dry soil. Use this technique
to learn how far to the side and how deep a single outlet
has wet your soil. You may need to repeat the test for
different times to wet the soil as deep as two feet. If your
soil has rocks or gravel that makes using
the soil probe difficult, you can always dig holes to see
how far the water penetrated. It’s best to wait 18 to 24
hours to dig in wet soil. Use this information to decide
how far apart to space bubblers, soaker hoses, or drip
emitters.
The type, size, and density of plants in the landscape
also affect water requirement. Saguaros and roses do
not require the same amount of water, for example.
A dense landscape, with many plants in a small area,
will require more frequent irrigations than a sparse
landscape. Exposure is also important. A rose in full
sun on the west side of your home will require more
water than one on the north side.
Where to Irrigate
Plants absorb water from the soil through roots. In a
natural setting, most of the plant’s roots spread to 1.5
to 4 times the width of the canopy and are within the
top two to three feet of soil. This is called the root
zone. Most of the water used by a plant comes from
outside the "canopy drip line" (figure 10). Shallow
or compacted soils can affect root distribution, as can
improper irrigation. Often it is not feasible to water the
entire root zone, but we should duplicate the natural
conditions as much as possible. One approach is to
water at least half of the root zone. This entails
watering from near the trunk out to and beyond the
ends of the branches. It is important to wet the same
area of soil to the same depth every time you water to
maintain a healthy, well distributed root system.
Percent of total water
absorbed
canopy
drip
line
Figure 10: Most water used by trees and
shrubs is absorbed outside the canopy
drip line.
Placement of Drip Emitters
Drip systems are the most efficient and accurate method
of applying water when properly designed, installed, and
operated. Poorly designed, installed, or operated systems
can lead to many problems. One of the most common is
too few emitters that are poorly spaced. All too often
only a single emitter is placed at the base of a
newly planted tree or shrub. In clay soils a single emtter
typically wets a 5' in diameter area, on sandy soils only
Irrigation
35
an area 2 feet in diameter (figure 9). Given the fact that
tree roots can grow up to 3 feet a year, after one year the
diameter of the root system could be 6 feet. A single
emitter with a 5' diameter wetting pattern could restrict
root development as early as the first year after planting.
For this reason, it is especially important to allow for the
placement of additional emitters early in a plant's life.
The size of the root system at plant maturity must also
be considered. The following chart shows the number of
one gallon per hour emitters recommended based on
canopy width at maturity and wetting at least half of the
root zone. This chart assumes two feet between emitters
on a sandy soil and five feet between emitters on a clay
soil. Use the soil probe technique to decide how wide
and deep the water has moved from a single emitter
after a certain amount of watering time. Space emitters
so wetting patterns meet or overlap slightly based on the
results of this test (figure 11).
The large number of emitters recommended, especially
on sandy soils, is impractical. However, plants in a
landscape share root zones and can share emitters. In
an example using a 24 inch soil wetting pattern, a 15 foot
canopy tree would require 63 emitters. A planting of five
large shrubs, each with a 4 foot canopy would require 5
emitter per plant or a total of 25 for the group.
If the tree and shrubs shared the same root zone area the
minimum
root zone
size
canopy drip line
wetted area
emitter
emission
point
Figure 11.
36
minumum number of emitters required to wet half of root
zone at maturity on sandy and clay soils.
Plant canopy width at
maturity (ft)
minimum
wetted area
(ft2)
number of emitters required
sandy soil
clay soil
2
4
2
0
4
14
5
1
6
32
10
2
total number of emitters needed would not be 88 (63 +
25), but instead, as few as 38 (63 - 25) emitters.
Drip emitters can be placed under a surface mulch or
underground with distribution tubing sticking
aboveground. Drip systems also do not lead to surface
compaction due to low flow rates.
Quantity of Water and Frequency of
Irrigation
Every irrigation should wet the soil to the depth of the
rooting zone. The rooting depth of turf, ground covers,
vegetables and flowers is typically 12 inches. The
rooting depth of shrubs is 18 inches. And the rooting
depth of trees is 24 to 36 inches. Use the soil probe test
to determine how long it takes to wet the soil to the
potential rooting depth. Water this same duration every
time. Frequent, shallow irrigations encourage a shallow
root system and an unstable plant. Also most plants
will use water that is available, although it may not be
needed, so frequent irrigations can waste water. The
Irrigation
37
soil should be allowed to dry between irrigations.
Many factors determine how much water a plant needs
and how often you should irrigate. We have already
discussed soil and plant types, size, and density.Along
with soil, plant type, plant size, and planting density is
the factor of weather. Plants use more water during the
hot summer than in the winter. They will also use more
water during an exceptionally hot summer than in an
average summer. Many established trees and shrubs- in
the hot, low desert areas of the state require between
0.6 and 0.8 inches of water per week in June during an
average summer. The following table shows how many
gallons this would be for different canopy sizes.
Established trees and large shrubs should not require
watering more frequently than oensctim
e aevteedryweweekelyk woarter reminimum
qruuirbesm, ereng
ta
inrdJluenses (ogfallons)
twoc.aN
noepw
yly planted trees and sh
wetted area
w
i
d
t
h
(
f
t)
their drought toleran(fct2e) , will need daily watering after
planting, tapering off gradually until establishment. The
following chart pertains to low desert areas. In higher
elevations weekly water requiremelnotws may be lesh
s.igUhse
the following chart as an aid to scheduling water times.
Suppo2se you have a 4deep, clay-type1soil and it take2s six
hours to wet the soil to a depth of two feet. You also
have a low water shrub with a ten foot wide canopy
7 es
and fi4ve one-gallon-1p4er-hour emitte5rs. Six hours tim
five emitters equals fifty gallons per irrigation. The
chart suggests that a ten-foot wide shrub would require
6
32
11
16
about thirty gallons every week or sixty gallons every
two weeks in June. Water the shrub once and watch for
the signs of drought: leaves curl, wilt, or turn yellow
and drop off. Most plants recover easily from a slight
wilt. If you see any of these signs within two weeks,
water but keep trying to stretch the durations between
waterings. If you do not see signs of stress within
two weeks you might want to water or wait until they
appear.
Xeriscaping
The term Xeriscape originated with the Denver,
Colorado Water Department in 1981 in response to
38
drought conditions occurring in Colorado. Xeriscaping
principles were developed through experience in a
number of different western states, including Arizona.
Xeriscape (pronounced zeer-i-scape) is water
conservation through creative landscaping. The term
Xeriscape means water conserving, drought tolerant
landscaping. Given that approximately one-half of the
per capita water demand in urban areas of Arizona is
for residential outdoor use, Xeriscaping can provide
significant impact in conserving our limited water
resources.
Xeriscaping takes a holistic approach to landscape
water conservation. It stresses the use of native and
drought tolerant plants and their use in appropriate
situations. But more than that xeriscaping involves
proper planning and design, installation and
maintenance practices.
There are seven basic principles of Xeriscaping. They
include:
— Water-wise planning and design.
— Low water use/drought tolerant plants.
— Limited lawn areas.
— Efficient irrigation design and equipment.
— Water harvesting techniques.
— Surface mulches and soil amendments (where
appropriate)
— Proper maintenance practices.
Water-wise Planning and Design
Many people create their own designs with excellent
results. Landscape professionals can also serve as
helpful resources. They can provide advise, critique, or
can develop the plans. Planning is the most important
step to a successful Xeriscape because it allows for
the installation of the landscape in phases, which
minimizes expenses.
Irrigation
39
The zoning of landscape plantings is one of the basic
concepts of Xeriscape design. The oasis zone is the area
in closest proximity to the house. Here, higher water
use plants are located to help cool the home through
shading and evapo-transpiration. This may
be the location for a small lawn area, annual flowers,
potted plants, cooling vines or a paved patio surrounded
by shrubbery and ground cover plants. A little farther
out from the house comes the transition zone, where
drought tolerant trees, shrubs and ground covers are
used in groupings to enhance the benefits of water
harvesting techniques. The arid zone lies beyond the
transition zone and is comprised of plants which need
little or no supplemental irrigation. The emphasis here is
on plants that can survive on rainfall alone. This is the
place to leave any natural vegetation that may have been
on the property.
Low Water Use/Drought Tolerant Plants
There is no shortage of beautiful drought tolerant native
plants in Arizona. But many introduced plants from arid
or semi-arid regions of the world are also drought
tolerant. Most importantly, select the right plant for the
right place. Be mindful not only of water requirements
but also of the factors of soil conditions, and exposure
to light, wind, and temperature extremes (both hot
and cold). Bear in mind that even native and drought
tolerant plants must have regular irrigation until they
are established.
Limited Lawn Areas
Locate turf only in areas where it provides functional
benefits, such as a children's play area or pet run. Turf
is best separated from landscape plantings so that it
may be watered separately. Often turf can be replaced
with other, less water demanding materials, such as low
water demanding ground covers, surface mulches, or
hard paving materials. Never locate turf areas on slopes
40
where water is lost to run-off.
Efficient Irrigation Equipment and Design
Match your irrigation method to the type of plant being
irrigation, drip or low volume spray emitters for
individual plants and spray irrigation for lawns. Drip
and low volume spray are the most efficient ways to
irrigate because they put the water where it is needed
and reduce run-off and evaporation. Use a timer or
controller to schedule irrigation and adjust as seasons
and weather changes. Combine plants with like water
requirements on a separate irrigation zone with its
own value that can be controlled by use of a timer or
controller.
Water Harvesting Techniques
Water harvesting techniques are used to channel runoff
water to planted areas or contain it for later use. A few
simple methods that direct water where it is needed
include sloping sidewalks and terraces, channeling or
collecting roof water, creating shallow basins around
landscape plantings, and the use of rock channels to
direct rain water (figure 12). By creating earth mounds
or berms at the edge of the property water can be
trapped on site. Locate plants where they can take
advantage of the extra water.
Mulch and Soil Amendments
Mulches are coverings placed on the soil under and
around plants. Typical organic mulches include;
compost, bark chips, ground wood, wood shavings,
and animal manures. Inorganic mulches include;
decomposed granite and other rock and gravel
materials. Mulches help hold in soil moisture, keep soil
temperatures cooler during the summer, reduce weed
growth, and in the case of organic mulches; reduce soil
compaction, improve water penetration, and add humus
to the soil. Soil amendments are organic materials such
as peat moss, animal manure and compost which are
Irrigation
41
mixed into the soil. Their use is beneficial in conserving
water, but should be limited to use in vegetable, flower
and ground cover beds where the entire potential root
zone can be modified. Never use soil amendments in
planting holes for trees and shrubs!
Proper Maintenance Practices
Plants that are healthy and properly maintained use
less water. Avoid over fertilizing and heavy pruning
which can promote excessive growth and increase
water needs. Mow lawns to the recommended height to
promote deep rooting and drought resistance. Keep
mower blades sharp; clean cuts lose less moisture than
inert
groundcovers
contouring
lawn
runoff
rock-lined
water detention
basin
2" perforated
pipes
Figure 12.
jagged tears. Control weeds that can compete with
desirable plants for water and nutrients. When possible,
water on an as-needed basis, taking into account the
weather, the climate, and the plants individual water
requirements.
42
Index
A
application rates 17, 18, 19, 24, 31, 32, 33
application uniformity 17
automatic valves 27
B
backflow prevention 25
bubblers 10, 19, 23, 24, 28, 34
C
chemigation 26
controller 21
D
distribution pipe 23
drip 21
drip and micro-sprinklers 18
drip emitters 7, 10, 18, 19, 23, 26, 28, 29, 30, 34, 35, 36
drip tubing 18, 19, 23, 26, 28
drought tolerant plants 5, 39, 40
E
effluent water 11, 12
evaporation 4
evapotranspiration 3, 4, 6
F
frequency of irrigation 37
I
installation 8, 17, 29, 30, 39, 40
irrigation controllers 28
irrigation losses 3, 8, 9
irrigation problems 31
irrigation scheduling 3, 9, 17, 25, 28, 32, 33
irrigation system components 23
irrigation system design 3, 11, 20
irrigation system layout 21
irrigation system maintenance 31
irrigation system selection 16
irrigation zones 20, 24, 25
L
low water use plants 5, 20
P
pipe 8, 22, 23, 28, 29, 30, 32, 43
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43
placement of drip emitters 35
plant water use 6, 7, 24
pressure regulators 26
Q
quantity of water 3, 37
R
root zone 9, 12, 13, 21, 27, 35, 36, 37, 42
S
salinity 12, 13
salt tolerance 13
sprinklers 16, 17, 18, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 32, 33
surface or flood irrigation 19
T
total dissolved salts 12
W
water harvesting 39, 40, 41
water quality 9, 11, 15, 16
water requirements 3
water supply 10, 11, 13, 16, 20, 21, 23, 25, 26, 31
water testing 12, 25
where to irrigate 35
X
xeriscaping 39
Z
zoning 40
44