|Efficient Use of Water in the Garden and Landscape
Jerry Parsons, Extension Horticulturist
Sam Cotner, Head of Horticulture Department
Roland Roberts, Extension Horticulturist
Calvin Finch, San Antonio Water System
Doug Welsh, Extension Horticulturist
Larry Stein, Extension Horticulturist
During 1984, an estimated 1.25 million acre feet of water were
used by Texans in the care and maintenance and residential landscapes.
Texas is expected to soon become the second most popular state
in the U.S. with two-thirds of the population located in urban/suburban
areas. With this growth, conservative estimates indicate water
needs will increase 75 percent by the year 2000. Thus, conservation,
reclamation and efficient use of water resources will become increasingly
Essentially all water used in Texas is derived from precipitation.
Part of the precipitation flows into streams, ponds, lakes and
reservoirs, and some of this eventually reaches the Gulf; another
portion infiltrates the soil to the rooting zone of plants; a
third portion percolates below the rooting zone and becomes groundwater.
Surface water sources are recharged rapidly, but groundwater
reservoirs such as the Ogallala Aquifer, are recharged very slowly.
The Ogallala Aquifer is slowly being exhausted in some areas of
heavy pumping. The proportion of precipitation received in Texas
that is returned to the atmosphere as water vapor is estimated
to be 70 percent from non-irrigated land areas and 2 percent from
irrigated areas. Most of this loss represents evaporation or transpiration
from plant surfaces.
Efficient, Responsible Water Use
The danger of exhausting valuable aquifers by excessive pumping
is paralleled by the threat of polluting the groundwater with
industrial, agricultural and home landscape contaminants. Nitrates
from excessive and untimely fertilization are especially threatening.
Plants, Soils and Water
When water is applied to the soil it seeps down through
the root zone very gradually. Each layer of soil must be filled
to "field capacity" before water descends to the next layer. This
water movement is referred to as the wetting front. Water moves
downward through a sandy coarse soil much faster then through
a fine-textured soil such as clay or silt.
If only one-half the amount of water required for healthy growth
of your garden or landscape is applied at a given time, it only
penetrates the top half of the root zone; the area below the point
where the wetting front stops remains dry as if no irrigation
has been applied at all.
Once enough water is applied to move the wetting front into
the root zone, moisture is absorbed by plant roots and moves up
through the stem to the leaves and fruits. Leaves have thousands
of microscopic openings, called stomates, through which water
vapor is lost from the plant. This continual loss of water called
transpiration, causes the plant to wilt unless a constant supply
of soil water is provided by absorption through the roots.
The total water requirement is the amount of water lost from
the plant plus the amount evaporated from the soil. These two
processes are called evapotranspiration. Evapotranspiration rates
vary and are influenced by day length, temperature, cloud cover,
wind, relative humidity, mulching, and the type, size and number
of plants growing in a given area.
Water is required for the normal physiological processes of
all plants. It is the primary medium for chemical reactions and
movement of substances through the various plant parts. Water
is an essential component in photosynthesis and plant metabolism,
including cell division and enlargement. It is important also
in cooling the surfaces of land plants by transpiration.
Water is a primary yield-determining factor in crop production.
Plants with insufficient water respond by closing the stomata,
leaf rolling, changing leaf orientation and reducing leaf and
stem growth and fruit yield.
Not all water is suitable for use as an irrigation source. Prior
to implementing an irrigation system, the water source should
be tested for water quality. The instructions for testing and
the testing results may be obtained from the Texas Agricultural
Extension Service or an independent water lab. The results of
the test will determine if the water is suitable for irrigation
or reveal if any special tactics will be required to overcome
Major factors in determining water quality are its salinity
and sodium contents. Salinity levels are expressed as categories
based on conductivity.
Category C-1 represents a low salinity hazard. Water in this
category has a conductivity of less than 2.5 millimhos/cm. It
can be used for most crops without any special tactics.
Category C-2 reflects salinity that results in a conductivity
of 2.5 - 7.5 millimhos/cm. The water in this category can be used
for tolerant plants if adequate leaching occurs.
Category C-3 is high salinity water that has conductivity in
the 7.5-22.5 millimhos/cm range. It can not be used effectively
on poorly drained soils. On well drained, low salt soils the water
can be used for salt tolerant plants if it is well managed.
Category C-4 water is very high salinity and cannot be used
for irrigation on a regular basis.
Sodium is a major component of the salts in most saline waters
but its impact can be detrimental to soil structure and plant
growth beyond its status as a component of salinity. The level
of sodium (Na) in irrigation water is another important factor
Table 1. Determination of soil moisture content.
How Soil Feels and Looks
|Soil Moisture Level
||Light (loamy sand, sandy loam)
||Medium (fine sandy loan, silt loam
||Heavy (clay loam, clay)
|No available soil moisture. Plants wilt. Irrigation
required. (First Range)
||Dry, loose, single grained, flows through fingers.
No stain or smear on fingers.
||Dry, loose, clods easily crushed and flows
through fingers. No stain or smear on fingers
||Crumbly, dry, powder, barely maintains shape.
Clods break down easily. May leave slight smear or stain
when worked with hands or fingers.
||Hard, firm baked, cracked usually too stiff
or tough to work or ribbon* by squeezing between thumb or
forefinger. May leave slight smear or stain.
|Moisture is available, but level is low. Irrigation
needed. (Second Range)
||Appears dry; will not retain shape when squeezed
||Appears dry; may make a cast when squeezed
in hand but seldom holds together.
||May form a weak ball** under pressure but is
still crumbly. Color is pale with no obvious moisture.
||Pliable, forms a ball; ribbons but usually
breaks or is crumbly. May leave slight stain or smear.
|Moisture is available. Level is high. Irrigation
not yet needed (Third Range)
||Color is dark with obvious moisture Soil may
stick together in very weak cast or ball.
||Color is dark with obvious moisture. Soil forms
weak ball or cast under pressure. Slight finger stain but
no ribbon when squeezed between thumb and fore finger.
||Color is dark from obvious moisture. Forms
a ball. Works easily, clods are soft with mellow feel. Stains
finger and has slick feel when squeezed.
||Color is dark with obvious moisture. Forms
good ball. Ribbons easily, has slick feel. Leaves stain
|Soil moisture level following an irrigation.
||Appears and feels moist. Color is dark. May
form weak cast or ball. Leaves wet outline or slight smear
||Appears and feels moist. Color is dark. Forms
cast or ball. Will not ribbon but shows smear or stain and
leaves wet outline on hand.
||Appears and feels moist. Color is dark. Has
a smooth, mellow feel. Forms ball and ribbons when squeezed.
Stains and smears. Leaves wet outline on hand.
||Color is dark. Appears moist; may feel sticky.
Ribbons out easily; smears and stains hand; leaves wet outline.
Forms good ball.
| *Ribbon is formed by squeezing and
working soil between thumb and forefinger.
**Cast or ball is formed by squeezing soil in hand.
Sodium levels are expressed as categories based on concentration
and impact on soils.
The S-1 category denotes low-sodium water. Water in this category
can be used for most plants without any special tactics.
S-2 water has a medium level of sodium. Its use may be a problem
on some fine textured soils.
S-3 water has high levels of sodium and will produce harmful
effects in most situations. Sometimes it is useful on soils with
high gypsum levels and in low salinity situations where it can
be chemically treated.
S-4 water has very high sodium levels and is generally unsatisfactory
as irrigation water.
There are critical growth periods when water stress is most
detrimental. It is imperative that a good moisture supply be maintained
during seed germination and seedling emergence from the soil.
Water transplants immediately. Many shallow-rooted plants and
newly planted trees and shrubs suffer water stress. Wilting followed
by browning leaf tips and edges are signs of water stress.
To determine if irrigation is needed, feel the soil in the soil
zone where most roots are located. Table 1 explains how to determine
the soil's moisture by feel. As you gain experience feeling the
soil and observing plant symptoms, it will help you time irrigations.
Proper watering methods are seldom practiced by most gardeners.
They either under- or over water when irrigating.
The person who under-waters usually doesn't realize the time
needed to adequately water an area; instead he applies light,
daily sprinklings. It is actually harmful to lightly sprinkle
plants every day. Frequent light applications wet the soil to
a depth of less than 1 inch. Most plant roots go much deeper.
Light sprinkling only settles the dust and does little to alleviate
drought stress of plants growing in hot, dry soil. Instead of
light daily waterings, give plants a weekly soaking. When watering,
allow the soil to become wet to a depth of 5 to 6 inches.
This type of watering allows moisture to penetrate into the
soil area where roots can readily absorb it. A soil watered deeply
retains moisture for several days, while one wet only an inch
or so is dry within a day.
In contrast, there are those who water so often and heavily
that they drown plants. Symptoms of too much water are the same
as for too little. Leaves turn brown at the tips and edges, then
brown all over and drop from the plant. These symptoms should
be the same, since they result from insufficient water in the
Too much water in a soil causes oxygen deficiency, resulting
in damage to the root system. Plant roots need oxygen to live.
When a soil remains soggy little oxygen is present in the soil.
When this condition exists roots die and no longer absorb water.
Then leaves begin to show signs of insufficient water. Often gardeners
think these signs signal lack of water, so they add more. This
further aggravates the situation and the plant usually dies quickly.
Thoroughly moisten the soil at each watering, and then allow
plants to extract most of the available water from the soil before
A mulch is a layer of material covering the soil surface around
plants. This covering befriends plants in a number of ways.
It moderates soil temperature, thus promoting greater root development.
Roots prefer to be cool in summer and warm in winter. This is
possible under a year-round blanket of mulch.
Mulch conserves moisture by reducing evaporation of water vapor
from the soil surface. This reduces water requirements.
Mulching prevents compaction by reducing soil crusting during
natural rainfall or irrigation. Falling drops of water can pound
the upper 1/4 inch of soil, especially a clay soil, into a tight,
brick-like mass that retards necessary air and water movement
to the root zone.
Mulching also reduces disease problems. Certain types of diseases
live in the soil and spread when water splashes bits of infested
soil onto a plant's lower leaves. Mulching and careful watering
reduce the spread of these diseases. Mulching also keeps fruit
clean while reducing rot disease by preventing soil-fruit contact.
Most weed seeds require light to germinate so thick mulch layer
shades them and reduces weed problems by 90 percent or more.
Any plant material that is free of weed seed and not diseased
is suitable for mulch. Weed-free hay or straw, leaves, grass clippings,
compost, etc., are all great. Fresh grass clippings are fine for
use around well-established plants, but cure them for a week or
so before placing them around young seedlings.
Mulch vegetable and flower gardens the same way. First get plants
established, then mulch the entire bed with a layer 3 to 4 inches
thick. Work the mulch material up around plant stems.
Organic mulches decompose or sometimes wash away, so check the
depth of mulches frequently and replace when necessary.
Recent research indicates that mulching does more to help newly
planted trees and shrubs become established than any other factor
except regular watering. Grasses and weeds, especially bermuda
grass, which grow around new plants rob them of moisture and nutrients.
Mulch the entire shrub bed and mulch new trees in a 4-foot circle.
Four distinct methods of irrigating are sprinkling, flooding,
furrow-irrigation and drip irrigation. Consider the equipment
and technique involved in each method before selecting the "right"
system. Select a system that will give plants sufficient moisture
without wasting water.
Sprinkler irrigation, or "hose-end overhead sprinkling" as it
is sometimes called, is the most popular and most common watering
method. Sprinkler units can be set up and moved about quickly
and easily. They are inexpensive to buy, but if used incorrectly
they can be extremely wasteful of water.
Sprinkler equipment varies in cost from a few dollars for a
small stationary unit to $50 or more for units that move themselves.
A solid-set sprinkler system for a small garden could cost more
than $100, although it is not necessary to spend that much. The
best investment is an impact-driving sprinkler than can be set
to water either a full or partial circle.
Sprinkler irrigation has its advantages. The system can be used
on sloping as well as level areas. Salt does not accumulate because
water percolates downward from the surface carrying salts with
it. Different amounts of water can be applied to separate plantings
to match plant requirements.
However, there are some drawbacks. Use sprinkler irrigation
early in the day to allow time for the soil surface to dry before
nightfall. Irrigation in a wind of more than 5 miles per hour
distributes the water unevenly. If you have poor quality water,
the mist which dries on leaves may deposit enough salt to injure
them. Strong winds may carry the water away to neighbors' yards.
Some water also is wasted by attempting to cover a square or rectangular
area with a circular pattern. Move the sprinkler unit at regular
intervals if the garden is larger than the sprinkler pattern.
With caged tomatoes or trellised crops, set the sprinkler on a
stand to allow the spray to arch up and over the top of the leaf
canopy. Improper timing and operating in wind or at night can
damage plants and waste water.
Flooding is one of the oldest irrigation methods. It is often
used in areas with extreme summer heat, especially in large farming
operations. It can also be used in the home garden.
First, a shallow dam is raised around the entire perimeter of
the area to be watered. Then, water is allowed to flow over the
soil until the dammed area is completely covered. Beneficial flooding
is possible only if the area is level and the soil contains enough
clay to cause the water to spread out over the surface and penetrate
slowly and evenly. The soil must not remain flooded with water
for more than a few hours.
Flood irrigation is useful where alkaline water causes a buildup
of salts to toxic levels in the soil. Flooding leaches (flushes
down) these excess soluble salts out of the soil. It is best to
do this type of flooding before spring fertilizing, tilling and
However, flood irrigation has its drawbacks. It can waste water
because it is easy to apply much more water than is required to
meet normal plant needs. Runoff is hard to avoid. Also, rapidly
growing plants are injured by the low oxygen level present (oxygen
starvation) in flooded soil, and fruits resting on flooded soil
stay wet, often rotting as a result.
Furrow irrigation is a popular method of applying water, primarily
to vegetable gardens. Successful furrow irrigation requires soil
with enough clay so that water flows along shallow ditches between
the rows and sinks in slowly. The water must reach the low end
of the rows before much has soaked in at the high end. Many sandy
or open soils are so porous that water seeps in too quickly, never
reaching the end of the row. To solve this problem, use short
rows in gardens with sandy soil.
Most gardens can be irrigated easily with the furrow method
by using a hoe or shovel to make shallow ditches. To test furrow
irrigation, make one shallow ditch from end to end and run water
down it. If the water runs 20 to 30 feet in a few minutes, that's
fine. If the water sinks in too fast at the high end, divide the
garden lengthwise into two or more runs and irrigate each run
separately. Make a serpentine ditch to guide the water up and
down short rows in small gardens on level ground. The number of
rows which can be irrigated at the same time depends on the volume
of water available and your ingenuity.
Leaves and fruit of erect plants such as beans and peppers will
stay dry during furrow irrigation. New seedlings can be watered
by running water as often as needed to keep the seedbed moist.
The surface soil of a raised bed does not pack as with sprinkler
irrigation, so there is less crusting. Only a hoe or shovel and
a length of hose are needed to get the water from the house faucet
to the garden.
But, furrow irrigation does have some disadvantages. Mature
fruits of vine and tomato crops usually rest on the soil. Some
will become affected with a soil rot after repeated
wetting. And it is difficult, if not impossible, to protect them
with mulch. Train vining plants away from furrows even though
it is not an easy task. In areas with salty water, salts accumulate
near the center of the row and can injure plants. If only a small
volume of water is available, water a few rows at a time and then
change to a new set. This can be time consuming and wasting water
at the ends of the rows is a common problem.
Trickle or drip irrigation is an improvement over all the above
as a watering technique. It applies a small amount of water over
a long period of time, usually several hours. This is discussed
in detail later in this publication.
USING WATER AROUND HOME TREES AND SHRUBS
Grass and/or weeds growing under and around trees and shrubs
compete for the same nutrients and water. When summer rainfall
is low and less than adequate watering occurs, competition for
water and nutrients imposed by weeds or grass substantially reduced
tree growth, bud development and fruit size. When competition
from grass is eliminated, roots are more evenly distributed, root
numbers increase and they utilize a larger volume of soil. Effective
soil utilization by a large root system means that fertilizer
and moisture will be used more efficiently.
Remove grass and/or weeds from beneath newly planted trees and
shrubs as soon as possible. The longer turfgrass grows under trees
and shrubs, the greater the reduction of new growth. There is
also a cumulative effect which may decrease tree growth for several
years. For instance, if the growth of a tree is reduced by 20
percent for one year because of grass competition, the growth
automatically is 20 percent less during the second year's growth.
Grass competition reduces growth by as much as 50 percent.
If trees and shrubs are surrounded closely by tenacious grasses
such as bermuda, remove or kill the turf. The safest grass killer
for use near young trees and shrubs is glyphosate, which is sold
as Roundup, Kleenup, Doomsday or Weed and Grass Killer.
This herbicide totally eliminates grasses and roots, yet is
inactivated upon soil contact. Use a piece of wood, cardboard,
etc, as a shield to prevent spray droplets from touching trunks
or foliage of desirable plants. Use only the amount of glyphosate
suggested on the product label.
Liberal watering offsets the retarding effect of grass. If the
competition of grass for water can be overcome by extra watering,
plants will grow much better.
Trees need a deep, thorough soaking once a week in the growing
season, either from natural rainfall or supplemental irrigation.
When irrigating, be thorough and allow the water to penetrate
deeply. To water large trees let water flow slowly onto an area
under the dripline of the tree for several hours.
Professionals indicate that large trees require more deep watering
than homeowners can imagine. Remember that watering which is adequate
for lawn grasses growing under trees is not adequate for actively
Young and mature pecans, which are popular lawn trees in many
areas, respond positively to irrigation. Irrigation can be very
beneficial if not necessary, in June, July, and August. Irrigation
often means the difference between a marketable and unmarketable
product. A dry June and July may cause many or all nutlets to
drop. Drought during July and early August can decrease nut size.
Pecans fill during August and September. Drought during three
months may cause nuts that are poorly filled. A dry September
and October may prevent shuck opening and cause a high proportion
of "sticktights". Drought-induced sticktights can be a serious
Growth of young, nonbearing pecan trees depends on a regular supply
of water from April bud break to mid-August. The frequency of
irrigation varies with the system used. However, avoid applying
too much water. An understanding of internal soil drainage prevents
overwatering. When too much water is supplied, oxygen is forced
out of the root zone and many serious problems result, including
- Growth stops.
- Minerals are not absorbed.
- Leaves turn yellow and remain small.
- Roots begin to die.
A guide for young tree irrigation is shown in Table 2. If soil
drainage is poor, apply 50 percent of this volume.
All bearing pecan trees respond positively to irrigation. In
general, pecans in good soil bear with only 32 inches of rainfall
from August to October. However, more water increases tree health
and regular production.
Table 2. Average weekly water requirements in gallons per tree.
|1-year old trees
|4- to 7- year-old trees
Pecans require 1 inch of water each week from April to October;
the optimum amount is 2 inches per week.
A bearing pecan tree has its greatest water needs during the
March, immediately before growth begins.
June, when nuts begin to size
Late July, when kernels begin to fall.
Severe drought during one of these four periods can cause complete
crop failure or serious loss. If these occur during the last period,
a poor crop results the following year.
Pecan roots can dry out and die if no rain occurs from September
to April. Therefore, consider a mid-winter irrigation to ensure
good tree health and regular production.
Water needs vary considerably among the turfgrasses. Consider
this when establishing a lawn, for it may significantly reduce
irrigation needs during the summer. Of the common turfgrasses
tall fescue requires the most water and buffalo-grass the least.
St. Augustine, hybrid bermuda grass and common bermuda grass have
intermediate water needs.
Lightly water newly seeded or sprigged lawns at frequent intervals.
Keep the seed or sprigs moist but not saturated during this initial
growth period. This may require watering four or five times on
hot, windy days.
The first 10 days to 2 weeks are especially critical. If young
plants dry out, they may die. After a couple of weeks root system
development should be well under way and the watering frequency
can be slowly reduced. At about 1 month after seedling or sprigging
the lawn it should be treated as an established lawn. Purple or
red colored bermuda grass may indicate seedlings are overwatered.
If this occurs, reduce watering and plants usually recover.
Water newly sodded lawns much like established lawns except
more frequently. After the sod is applied, soak it with enough
water so that the soil under the sod is wet to a depth of 2 to
3 inches. Each time the sod begins to dry out, resoak it. Roots
develop fairly rapidly and within 2 weeks or so the sod can be
treated like an established lawn.
Ideally, a lawn should be watered just before it begins to wilt.
Most grasses take on a dull purplish cast and leaf blades begin
to fold or roll. Grass under drought stress also shows evidence
of tracks after someone walks across the lawn. These are the first
signs of wilt. With careful observation and experience, one can
determine the correct number of days between waterings. Common
bermuda grass lawns can go 5 to 7 days or longer between waterings
without loss of quality.
Early morning is considered the best time to water. The wind
is usually calm and the temperature is low so less water is lost
to evaporation. The worst time to water is late evening because
the lawn stays wet all night, making it more susceptible to disease.
When watering a lawn, wet the soil to a depth of 4 to 6 inches.
Soil type affects the amount of water needed to wet soil to the
It takes about 1/2 inch of water to achieve the desired wetting
depth if the soil is high in sand, and about 3/4 inch of water
if the soil is a loam. For soils high in clay, an inch of water
is usually necessary to wet the soil to the desired depth.
If waterings are too light or too frequent the lawn may become
weak and shallow-rooted, which in turn makes it more susceptible
to stress injury.
Use the following steps to determine the amount of water your
sprinkler or sprinkler system puts out and check its distribution
pattern at the same time.
- Determine the rate at which your sprinkler applies water to
- Set out three to five empty cans in a straight line going
away from the sprinkler. Set the last can near the edge
of the sprinkler's coverage.
- Run the sprinkler for a set time such as 1/2 hour.
- Measure the amount of water in each can.
- Each can will contain a different amount of water. Usually,
the can closest to the sprinkle will have the most water.
The sprinkler pattern must overlap to get an even wetness
of the soil. Use this information to find out how long it
takes your sprinkler to apply 1 inch of water. For example,
if you find that most cans contain about 1/4 inch of water
after the sprinkler runs 1/2 hour, it would take 4 x 1/2
or 2 hours to apply 1 inch.
- Run the sprinkler or sprinkler system long enough to apply
at least 1 inch of water or until runoff occurs. If runoff occurs
- Stop sprinkler and note running time.
- Allow water to soak in for 1/2 hour.
- Start sprinkler.
- If runoff occurs, repeat above steps until at least 1
inch of water has been applied and allowed to soak into
- Do not water again until the lawn has completely dried out.
(This usually takes 5 or 6 days.)
- Apply enough water to wet the soil to a depth of 4 to
- Avoid frequent light applications of water.
- Water in early daylight hours.
- Select a turfgrass with a low water requirement.
- Avoid using soluble nitrogen fertilizers. (They promote
high growth rates which, in turn, increase water requirements
of the plant.)
Many soils will not take an inch of water before runoff occurs.
If this is a problem with your lawn, try using a wetting agent,
also called a surfactant, which reduces the surface tension of
water making it "wetter." This "wetter" water runs into the soil
at a faster rate and goes deeper than water in a non-treated soil.
There are a number of wetting agents available; apply them according
to directions on their labels. If this does not solve to runoff
problem, it may be necessary to apply 1/2 inch one day and 2 inch
the next day.
Generally speaking, if you keep your tomatoes happy, the rest
of the vegetables will receive enough water. Obviously, irrigating
a garden containing many kinds of vegetables is not simple. Early
in the season when plants are young and have small root systems,
they remove water from the soil near the center of the row. As
the plants grow larger, roots penetrate into more soil volume
and withdraw greater quantities of water faster.
In sandy loam soils, broccoli, cabbage, celery, sweet corn,
lettuce, potatoes and radishes have most of their roots in the
top 6 to 12 inches of soil (even though some roots go down 2 feet)
and require frequent irrigation of about 3/4 to 1 inch of water.
Vegetables which have most of their root systems in the top 18
inches of soil including beans, beets, carrots, cucumbers, muskmelons,
peppers and summer squash. These vegetables withdraw water from
the top foot of soil as they approach maturity and can profit
from 1 to 2 inches of water per irrigation.
A few vegetables, including the tomato, cantaloupe, watermelon
and okra, root deeper. As these plants grow they profit from irrigations
of up to 2 inches of water.
For fruiting crops, the most critical growth stage regarding
water deficit is at flowering and fruit set. Moisture shortage
at this stage may cause abscission of flowers or young fruits,
resulting in insufficient fruit for maximum yield.
The longer the flowering period, the less sensitive a species
is to moisture deficits. For example, the relative drought resistance
of beans during flowering and early pod formation is the result
of the lengthy flowering period --30 to 35 days with most varieties.
Slight deficits during part of this period can be partially compensated
for by subsequent fruit set when the water supply is adequate.
More determinate crops such as corn or processing tomatoes are
highly sensitive to drought during the flowering period.
In terms of food production, the period of yield formation or
enlargement of the edible product (fruit, head, root, tuber, etc.)
is critical for all vegetables and is the most critical for non-fruiting
crops. Moisture deficits at the enlargement stage normally result
in a smaller edible portion because nutrient uptake and photosynthesis
Irrigation, especially over irrigation during the ripening period
may reduce fruit quality. Ample water during fruit ripening reduces
the sugar content and adversely affects the flavor of such crops
as tomatoes, sweet corn and melons. Moisture deficits at ripening
do not significantly reduce yield of most fruit crops, irrigate
at this time with extreme caution.
DRIP IRRIGATION FOR THE HOME LANDSCAPE, GARDEN AND ORCHARD
One of the best techniques to use in applying water to home
landscapes, gardens and orchards is drip irrigation. This is the
controlled, slow application of water to soil. The water flows
under low pressure through plastic pipe or hose laid along each
row of plants. The water drops out into the soil from tiny holes
called orifices which are either precisely formed in the hose
wall or in fittings called emitters that are plugged into the
hose wall at a proper spacing.
Use drip irrigation for watering vegetables, ornamental and
fruit trees, shrubs, vines and container grown plants outdoors.
Drip irrigation is not well suited for solid plantings of shallow-rooted
plants such as grass and some ground covers.
The basic concepts behind the successful use of drip irrigation
are that soil moisture remains relatively constant, and air, as
essential as water is the plant root system, is always available.
In other watering methods there is an extreme fluctuation in soil
water content, temperature and aeration of the soil.
Soil, when flooded or watered by sprinkler, is filled to capacity.
It is then left to dry out, and often it is not until the plant
begins to show signs of stress that it is watered again. When
the soil is saturated in this way, there is little or no available
oxygen; at the end of the cycle there is insufficient water. Drip
irrigation overcomes this traditional watering problem by keeping
water and oxygen levels within absorption limits of the plants.
It frequently (even daily) replaces the water lost through evaporation
and transpiration (evapotranspiration). In addition to maintaining
ideal water levels in the soil, this also prevents extreme temperature
fluctuations which result from wet-dry cycles associated with
other watering methods.
With proper management, drip irrigation reduces water loss by
up to 60 percent or more as compared to traditional watering methods.
These methods deliver water at a faster rate than most soils can
absorb. Water applied in excess of this penetration rate can only
run off the surface, removing valuable topsoil and nutrients.
With drip irrigation the water soaks in immediately when the flow
is adjusted correctly. There is neither flooding nor run-off,
so water is not wasted. With a properly used drip irrigation system,
all of the water is accessible to the roots. Watering weed patches,
walkways and other areas between plants and row is avoided. Wind
does not carry water away as it can with sprinkler systems, and
water lost to evaporation is negligible.
Drip irrigation requires little or no time for changing irrigation
sets and only about half as much water as furrow or sprinkler
irrigation because water is delivered drop by drop at the base
of the plants.
Water shortage and high energy costs motivate gardeners to harvest
the greatest possible yield from every precious drop of water.
If you have shied away from installing a drip irrigation system
because it looked too complicated or too costly, this publication
explains how to have one easily and economically.
The financial investment is reasonably small if you are willing
to spend a few hours to plan, assemble and install the system.
Savings in water combined with increased yield and quality of
vegetables and flowers more than pays for the cost of parts to
maintain a drip system.
The life of a drip system is extended by proper design, proper
filtering, avoiding puncture with tillage tools, mulching over
plastic lateral driplines to shield them from sunlight, and flushing
and draining lines and storing system components inside a warm
building before hard freezing temperatures arrive.
The 3- to 5-gallons-per-minute flow from a typical house faucet
limits the area which can be adequately irrigated to usually not
more than 1,500 to 2,000 square feet.
From $15 to more than $30 per 100 feet of row can be spent for
equipment in an average sized home garden, depending on whether
it is simple or has fancy automatic controls, pressure regulators
and fertilizer injectors. As with most tools and machines, the
simpler the better.
The two basic kinds of drip irrigation systems which have worked
best for Texas growers are the two-channel plastic tubing represented
by IRS Bi-Wall and Chapin Twin-Wall, and the plastic pipe with
insert emitters represented by Submatic, Melnor Tirosh, Spot,
Microjet and many others. The emitters are made by cutting 1-foot
lengths of microtubing.
When planning a drip system, consider your needs, one at a time:
- A source of clear water which flows at a rate of at least
2 to 5 gallons per minute with at least 30 to 40 pounds pressure
is needed. Clean water is essential for successful drip irrigation
because sand, silt, organic material and other foreign material
can easily clog small emitter openings. Most city water sources
do not require a filter; however, some gardeners add a filter
to avoid clogging. The filtration system required depends on
the type and quantity of foreign materials in the water and/or
- Generally, a screen-type filter is best. A filter system in
the main line near the faucet is much easier to maintain than
several filter systems scattered throughout the irrigation system.
Y-type, in-line strainers containing single, 100-mesh, corrosion-resistant
screens (such as stainless steel or bronze) are usually adequate
for filtering small amounts of sand, rust particles, etc. Filters
with replaceable cartridges, synthetic-fiber fabric elements
or multi-stage screens such as 100- and 180-mesh are required
where water contains larger amounts of sand. Filters should
be equipped with cleanout or flush valves to easily remove trapped
particles. Daily flushing is necessary where water contains
moderate amounts of sand or other material. Screens and filter
cartridges need thorough cleaning or replacing periodically,
depending upon the amount of foreign material in the water.
- A decrease in water pressure and volume delivered can signal
filter clogging. A decrease in flow in spite of good pressure
in the lines indicates emitter clogging. All water from streams
and underground sources contains dissolved materials known chemically
Most water does not contain enough salt to be injurious to plants.
However, irrigation water adds salt to the soil, where it remains
unless it is removed in drainage water or the harvested crop.
When the amount of salt added to the soil exceeds the amount removed,
salt accumulates until the concentration in the soil may become
harmful to plants.
The principal effect of salinity is to reduce the availability
of water to the plant; however, certain salts or ions may produce
specific toxic effects. Poor quality irrigation water containing
moderate amounts of salt often can be used more successfully with
drip irrigation than with sprinkler or surface irrigation. Less
total salt is added with drip irrigation since less water is applied.
In addition, a uniformly high soil moisture level is maintained
with drip irrigation, which keeps the salt concentration in the
soil at a lower level.
Salts accumulate in the soil around the edges of the west area
under drip irrigation emitters, and some leaching (removal of
salts with drainage water) may be required. Sufficient rainfall
is received in much of the state to accomplish any required leaching
of salts. However, extra irrigation water may be required in some
areas to leach accumulated salts from the root zone. Operating
the system when the crop's water requirement is low can probably
accomplish required leaching of salts in most cases.
- Locate the area to be irrigated as closely as possible to
a faucet. If the area is more than 100 feet from the faucet
it may be difficult to get enough volume to run the drip system
properly in a large area. Use 5/8-inch or 3/4-inch hose from
the house faucet to the header in
the area to be irrigated. Usually a 5/8-inch hose is a sufficient
line size for normal gardens. Garden rows should be level or
only slightly downhill (not more than 1 to 2 percent grade)
even if it is necessary to run them on the contour (around the
hill instead of up and down it). Place small irrigation pipes
(drip hoses) right along the row; water drips out more uniformly
when the rows are level or slightly downhill. Transport water
from the source to the high side of the area to be irrigated.
If fruit and ornamental trees are to be drip-irrigated, use
insert emitters. The number of emitters per tree or plant depends
on plant size. A large fruit or ornamental tree having a canopy
spread of 15 feet or more in diameter needs six emitters. A smaller
tree or shrub needs one emitter for each 2 1/2 feet of canopy
diameter. The number of emitters multiplied by the rated output
per emitter gives the flow rate needed to irrigate all the trees
and shrubs simultaneously. For example, if there are 12 trees
on which 72 emitters will be used, each with a rated output of
1 gallon per hour at 15 pounds per square inch, the flow rate
will be 72 gallons per hour or 1.2 gallons per minute. A 1/2 inch
main line is sufficient according to the following guidelines.
Make a sketch of the area to be irrigated. Use graph or grid
paper to draw the area's shape using a scale of 1 inch to 5 to
Measure the length and width of the area. The distance from
the water source to the edge of the area to be irrigated is the
length of garden hose or plastic pipe needed to connect to the
Draw in the actual lines of drip hose required. If planning
a garden, a drip hose will be run down each row. Count the number
of rows and multiply the number of major rows by the row length
to get the total length of drip hoses needed. If you run several
rows close together (only a few inches apart) to create a bed
culture, consider using one drip hose if it is up to 18 inches
wide and two drip hoses if it is 24 to 36 inches wide. If wide
beds are used for planting flowers, use one drip hose every 18
Other helpful facts involve the direction of downward slope
in the garden and the gallons per minute delivered by your faucet.
Use a container of known volume, such as a 5-gallon pail, and
a watch to estimate gallons per minute.
INSTALLING A DRIP SYSTEM
When buying irrigation equipment avoid mixing brands of fittings,
hoses and emitters unless they are compatible. The design and
installation of Bi-Wall and Twin-Wall drip tubing and the design
and installation of Submatic, Melnor, Spot and Microjet emitter
systems are discussed separately so that the instructions are
easier to understand.
Table 3. Plastic line sizes for lengths less than 100 feet.
|Flow rate (gpm)
||Line size (inches nominal)
|1/2 to 2
2 to 4
4 to 8
When planning a Bi-Wall or Twin-Wall system, use a 1/2-inch
(16 millimeter) main water supply plastic hose (header) to feed
the water into the drip tubing which runs alongside each row.
Most house faucets supply enough water to run 200 to 300 feet
of drip tubing at once. Divide irrigation systems for larger areas
into two or more sets when the water volume is insufficient to
cover the whole area at once.
Parts needed for a drip tubing system with a header are a hose
long enough to reach from the house faucet to the header, a 1/2-inch
female hose connector, a 1/2-inch diameter header long enough
to connect all the drip tubes, an ear tee for each drip tube,
a drip tube for every row, a nylon string or strong wire to tie
the ends of the drip tubing and a sharp knife.
When a header is used, begin the installation by running a hose
from the house faucet to a female hose connector which is installed
in the end of the header closest to the faucet. The other end
of the header is plugged or folded back and tied off. Be sure
the header spans the entire width of the area to be irrigated
on the high side.
Place the correct lengths of Bi-Wall drip tubing along each
row. Plan rows to make the best use of water.
Small plants such as carrots, onions, radishes, lettuce, bush
beans, etc., can be double-rowed; that is, seed can be planted
on each side of the drip tubing.
To join the Bi-Wall tubing to the header pipe (the main water
supply), use a connecting attachment called an ear tee. At each
row, punch a small hole in the side of the 16-millimeter header
tubing facing down the row. Use a blunt eight penny nail to punch
the holes. Push the ear tee into the hole and wrap the two ears
around the header. To secure the far end of the Bi-Wall, fold
back 2 inches and tie with a string. If the water contains sand
or dirt particles, screw a filter to the hose connector as sand
particles and other trash can clog openings in the Bi-Wall tubing.
All of the drip irrigation fittings are connected to the plastic
tubing in the same manner. For the hose connector, push the 16-millimeter
header over the shaft and under the locking collar. When the header
is as far as you can push it, pull back on the tubing. This binds
the tubing under the locking collar. To disassemble, reverse the
procedure. For installing Bi-Wall tubing, push it on the ear tee
as far as it will go; push the collar outward, then grasp the
Bi-Wall tubing and pull back on it while holding the ear tee in
place with the other hand. This binds the Bi-Wall tubing under
the locking collar. Note the difference in the locking collar
for the Bi-Wall and the header. If irrigating only one row with
Bi-Wall, put a wide Bi-Wall collar on the hose connector, install
it in the Bi-Wall and fasten it to a water hose or faucet just
as for the header. It may be necessary to twist the locking collar
to allow the Bi-Wall to go all the way up.) Work the locking collar
down on the Bi-Wall, then hold the ear tee in one hand and pull
on the Bi-Wall tubing with the other hand. If it leaks around
the collar on the ear tee, push the Bi-Wall farther up on the
eat tee, twist the locking collar again and pull on the tubing.
The notch on the collar should be over the top of the Bi-Wall.
The second type of drip irrigation system involves the use of
insert emitters. When designing a drip system with insert emitters,
strive to have the same amount of water flowing out of all emitters
in the system. Secondly, have the flow rate regulated so that
water drips into the soil without puddles forming on the surface.
Insert emitter systems are ideally suited for irrigating trees,
which are planted farther apart than garden crops, flowers or
Trees previously irrigated by the other methods change their
root systems when drip irrigation is used. New feeder roots concentrate
near the emitters and become major suppliers. It is best to start
drip irrigation at the beginning of spring growth to allow time
for new roots to develop before hot weather arrives. If drip irrigation
is initiated in midsummer, an occasional supplemental irrigation
by the old method is recommended to avoid plant stress.
Soil texture is of primary importance in the design and use
of drip irrigation. It directly affects the number or placement
of emitters. In sandy soil where spaces between sand grains are
relatively large, gravitational forces affect water movement more
than capillary action. As a result, water moves down rather than
laterally through the soil. In finer soils such as clay, capillary
action is much stronger and water spreads laterally before penetrating
very deeply. An emitter in sandy soil will water an area with
a diameter of about 15 inches, while in clay soil the same emitter
will water an area up to 2 feet in diameter. Since the same amount
of water is released in both cases, the sandy soil obviously receives
deeper watering than the clay.
The following chart on emitter placement suggests a 1-gallon-per-hour
emitter at the base of the plant, assuming you have a low shrub
in sandy soil. In fact, placing two 1/2-gallon emitters, each
about 9 inches from the base, increases the area of coverage while
using the same amount of water. Increasing the wet area encourages
wider development of the root system, and watering time is reduced
somewhat. However, remember that smaller volume emitters clog
more easily than larger volume emitters.
When working with vegetable crops and sandy soil, use closer
spacing (12 inches) to ensure that all shallow roots receive sufficient
moisture. With finer soils, use greater distances between emitters
while still ensuring proper coverage. To get a better idea of
soil structure experiment with slow water applications to observe
lateral movement and depth of water penetration. Observe the application
rate and time so better decisions on emitter placement, as well
as watering practices, can be made. Be sure that a sufficient
percentage of the root zone is watered. Shallow root zones require
emitters with closer spacing; deep roots allow wider spacing.
The widest spacing to use safely on vegetables and ground cover
is closer than the narrowest required by tree crops. This is shown
in the table on the number and placement of emitters.
Water quality may be a factor in emitter location since salts
concentrate at the edges of the wet area. It may be necessary
to locate emitters so that wet areas overlap the tree trunk to
prevent harmful salt accumulations near the trunk.
A popular emitter arrangement for large trees such as pecans
uses a loop which circles the tree between the trunk and the dripline.
The lateral pipeline which carries water along each row of trees
is under ground. A 1/2-inch or 3/8-inch polyethylene pipe connected
to the lateral near each tree extends to the soil surface and
circles the tree. The tree loop is usually 6 to 12 feet long initially
and contains one or two emitters. Additional lengths of pipe 8
to 12 feet long, each containing another emitter, are connected
to the initial loop as the trees grow and require more water.
Large pecan trees may require tree loops with five to nine emitters.
In-line emitter arrangements have been used satisfactorily for
smaller trees such as apples, peaches and citrus. Install two
or four emitters in the lateral so that wet areas overlap in line
with the tree row.
Emitter selection and performance are keys to the success of
all drip irrigation systems. Some emitters perform satisfactorily
underground while others must be used only above ground. Emitter
clogging is still a major problem in drip irrigation. Emitter
openings must be small to release small amounts of water, consequently,
they clog easily.
Table 4. Selection, number and spacing of emitters and orifices.
|Number of emitters or orifices
||Placement of emitters or orifices
|Low shrubs (2-3 feet)
|Shrubs and trees (3-5 feet)
||6-12 inches either side
|Shrubs and trees (5-10 feet)
||2 feet from tree equally spaced
|Shrubs and trees (10-20 feet)
||3 feet apart equally spaced
|Shrubs and trees (20 feet or higher)
6 or more
||4 feet apart equally spaced/tr>
|Containers (Potted plants)
|Vegetables (closely spaced)
||every 16-24 inches
|Vegetables (widely spaced)
one per plant
Emitters are more easily observed, cleaned and oriented near
the tree when they are located on the soil surface, although drip
systems with underground emitters are out of the way. Some emitters
can be flushed easily to remove sand or other particles which
cause clogging, while others are more difficult to clean.
Ease of installation and durability are important considerations
in emitter selection. Most emitters are either connected in-line
or by attaching to the lateral. In-line connections are made by
cutting the pipe and connecting the emitter to the pipeline at
the cut. Clamps, which increase costs, are required for connecting
emitters in some pipes. Check the pipe and in-line emitters for
correct fit before purchasing. Emitters which attach to the lateral
are either inserted into the pipe or clamped to it.
The flexibility of a drip irrigation system makes it ideal for
most landscapes. When native plants are transplanted they often
require watering for the first year or so until they establish
a root system. After that they usually survive on natural rainfall.
As plants grown and watering needs increase, more emitters can
be installed very easily. Or, 1 gallon emitters can be replaced
with 2- or 4-gallon-per-hour emitters.
In landscaping, plants with different watering requirements
must frequently be mixed together. Some ornamentals require occasional
deep watering, while others prefer more frequent shallow watering.
Differing needs can be satisfied through the number or size of
emitters by placing either a greater number of emitters or by
using emitters with a greater flow rate for plantings requiring
extra water. In clay soils it is best to increase the number of
emitters rather than the rate of flow since soil density limits
Once the system is set up this way, maximum benefit for all
plants is achieved by several shallow waterings--leaving the water
on for a short time (20 minutes to 2 hours) with an occasional
deep watering (several hours) as needed, depending on season,
plants and soil type.
Burial of the drip system is usually preferred by landscapers
and ornamental gardeners. Generally 3 to 4 inches deep is sufficient.
This not only hides the tubing from view but also adds to the
system's life expectancy. Most emitters can also be buried, but
check them occasionally. Rodent damage (sometimes they chew through
the tubing) and accidental damage from shovels or tillers are
problems associated with buried systems. Repairing cut or punctured
laterals is easy with a couple of connectors and a new section
Drip irrigation is the best method for watering landscape trees
also. A tree with only 25 percent of its roots wet regularly will
do as well as a tree with 100 percent wetting at 14-day intervals.
This saves water in drought situations by wetting only part of
the root zone. Thus a single lateral line is often sufficient
for even large trees.
Remember that the root system grows more vigorously in moist
soil. If emitters are placed on only one side of a tree, the root
system is not balanced and stability is threatened. In one experiment
with drip irrigation, a large crop of trees was blown over in
a storm because the roots had been watered on one side only.
When watering closely spaced plants such as garden crops, flowers
or shrubs using insert emitters, a system must have the capability
to maintain uniformly moist soil near the surface along any row
where you wish to germinate seeds.
It is not feasible to place an emitter where each plant will
grow. You do not use the same spacing for all vegetables and flowers
and you must not grow the same kind of plant in the same spot
year after year. All things considered, a spacing of 2 feet between
emitters is best for most closely spaced plants and soils; a spacing
of 18 inches might be better in very sandy soil.
Water is not wasted with 2-foot spaces even if plants are set
4 or 5 feet apart. Roots soon penetrate the soil around the plant
in a radius several feet from the stem, and absorb water from
every cubic inch of this soil.
Knowing the total length of a drip hose required allows you
to buy a ready-made kit with emitters already inserted in the
hose. Usually, hose length in these kits is either 50 or 100 feet.
The better kits have a filter and flow control of some sort.
Installing these kits is simple. Lay enough garden hose to reach
from the house faucet to the area to be irrigated, attach the
hose end to the coupling on the emitter hose and unroll the hose
down the first row. At the end of the row, curve the hose back
up along the second row and so on for remaining rows. If the kit
has a Y hose for equal lengths of hose connected to each leg of
the Y, put the Y near the center row at the high end. If there
is extra hose, run the excess back over the last row.
Taking one step at a time in customizing a drip system to fit
your planting area is fun and easy. First, select an emitter that
delivers 1 to 2 gallons per hour when operated in a pressure range
of 2 to 10 pounds per square inch. One emitter commonly used in
Texas is rated at 2 gallons per hour when operated at a pressure
of 10 pounds per square inch. When operated at 2 pounds per square
inch, this same emitter delivers 1 gallon per hour. In actual
practice the emitter would be operating at a pressure somewhere
between these two extremes. Emitter systems with insets irrigate
most uniformly when the pressure in the hose along the row is
maintained in a range of 3 to 6 pounds per square inch. The lower
the pressure, the greater the effect of elevation changes.
Water flow through a pipe is slowed by the friction it creates.
That is why water flows faster from the emitter nearest the header
and slowest from the emitter farthest from the header. Keep this
difference as small as possible. Well-designed small systems can
be operated with no more than 10 to 15 percent variation in flow
rate. Design your system for a uniform flow rate by limiting the
emitter hose length to less than 50 feet when the emitters are
2 feet apart on 3/8-inch hose.
With row lengths of 60 to 100 feet select 1/2-inch diameter
hose. If the 3/8-inch hose is used for runs up to 100 feet, a
drop in flow rate of more than 25 percent from the head to tail
of the hose will occur. Water is wasted at the beginning of the
row to get enough water into the soil at the end of the row. If
the garden is level, it is easy to shorten the length of run by
placing the header in the center (halfway down the length of the
garden). To keep the water volume adequate increase the diameter
of the supply hose or main to 3/4 inch.
If the garden slope is only slight and there are only a few
rows, put the header on the high end. For steep slopes where rows
must be contoured, run the header down the slope and the emitter
hose across the slope with the contour.
Now determine if the water supply is sufficient for the drip
system to work properly. Count the number of emitters and multiply
by the rated gallons per hour of the emitter. Divide this number
by 60 to get the gallons per minute your water source must supply
to allow the system to irrigate uniformly. For example, 100 emitters
multiplied by 2 gallons per hour per emitter equals 200 gallons
per hour, 200 gallons per hour divided by 60 equals 3.3 gallons
per minute. If your water supply is 5 gallons per minute, design
the header hose to irrigate the garden in one set; if your water
supply is only 2 to 3 gallons per minute, divide the header into
two sets using a tee with two shutoffs to permit irrigating each
half of the garden separately.
Select the proper size main and submain (header) hoses next.
For flow rate up to 3 gallons per minute, 1/2-inch diameter hose
is adequate for the main hose from the faucet to the header and
for the header, too. When a flow of 3 to 6 gallons per minute
is required to satisfy the emitter hose, the main hose carrying
water to the header should be 3/4 inch in diameter and the header
can be 1/2-inch diameter hose.
For example, here is a hypothetical garden 20 feet wide and
30 feet long, with 25 feet from the hose faucet. It has six drip
emitter hoses with emitters 2 feet apart in the hose. Starting
at the house faucet, a drip system would require one 80-mesh hose
strainer, 25 feet of 1/2-inch supply hose with threaded coupling,
one 1/2-inch female swivel hose thread poly compression tee, 20
feet of 1/2-inch header hose, four male hose thread poly compression
tees, six 1/2-gallon-per-minute flow control valves, 180 feet
of 3/8-inch male hose compression couplings with caps, 100 emitters
which deliver 1 to 2 gallons per hour and one twist punch. Include
several repair couplings and a dozen hole or 'goof' plugs to help
repair accidents. Row shutoffs and flow control valves can be
omitted, but the system would be less versatile and less uniform
in flow rate.
Installing this emitter hose system requires only a knife to
cut the hose and a twist punch or hand punch to install insert
emitters. Some hose comes with emitters already installed, and
the cost is only slightly more.
Assemble the system starting at the house faucet. Lay hose from
the faucet to the soil at the edge of the garden, leaving it slack.
Sink wooden stakes in the soil to hold the hose and fittings where
you place them. Measure pieces of header hose and push them into
the compression fittings (tees) so that the drip hose lines up
exactly with a center of the row. Then, punch a hole with the
twist punch along the top side of the drip hose every 2 feet and
press an emitter into each hole. Turn on the water to flush any
foreign particles out of the end of the hoses. When the lines
are cleaned, stop the water and cap the end of each drip hose.
Now it's ready to irrigate.
OPERATING A DRIP SYSTEM
Operating a drip system is a matter of deciding how often to
turn it on and how long to leave it on. The object is to maintain
adequate soil moisture without wasting water by applying too much.
Anyone can turn on a faucet for an hour or two every day, and
some drip system manufacturers advise leaving systems on continuously
for the entire growing season. Not all gardens, however, use the
same amount of water daily. Knowing how often and how long to
water depends on the system's rate of delivery, soil type, varying
weather conditions, kinds of plants, their growth stage and cultural
practices in use. Irrigating trees has the same restrictions.
Water requirements are influenced by tree size and growth as well
as rainfall, temperature, relative humidity and wind velocity.
Ideal system operation applies just enough water to replace the
amount used by the plants the previous day. Uniform soil moisture
content is maintained and the volume of moistened soil neither
increases nor decreases.
Estimate daily operating time in hours by dividing the daily
water requirement of each plant in gallons by the application
rate to each plant in gallons per hour. Continuous irrigation
may be required for short periods when water use by the plants
is maximum, but continuous operation when it is not required offsets
the basic advantage of minimum water application with drip irrigation.
The object of each watering is to bring the moisture level in
the root zone up to a satisfactory level. Any more means cutting
off necessary oxygen along with the loss of water and nutrients
below the root zone. The system is then run again before the satisfactory
moisture levels in the soil is lost. If plants are showing signs
of insufficient moisture and watering duration is long enough
(see Table 5), then shorten intervals between watering.
Table 5. Watering time (in hours) per irrigation.*
Type of plant (height)
|Low shrubs (2-3 feet)
|Shrubs and trees (3-5 feet)
|Shrubs and trees (5-10 feet)
|Shrubs and trees (10-20 feet)
|Shrubs and trees (20 feet or higher)
|Vegetables -- close spacing
|Vegetables -- wide spacing
|* Use this guide, experiment and
observe plants and take moisture readings in root zone if
possible. Adapt the guide according to your findings. Remember,
the object is to adequately water the root zone but no more.
Table 6 give the amount of water various plants need under a
range of temperature conditions. This is evapotranspiration. It
considers the water used by the plant as well as the water evaporated.
Plants need three to four times as much water in hot weather as
they do in cool weather. Both tables are needed to calculate the
number of waterings each week.
Table 6. Irrigation time needed each week.*
Type of plant (height)
Hours of Watering
|Low shrubs (2-3 feet)
|Shrubs and trees (3-5 feet)
|Shrubs and trees (5-10 feet)
|Shrubs and trees (10-20 feet)
|Shrubs and trees (20 feet or higher)
|Containers (Potted plants)
|Vegetables -- close spacing<
|Vegetables -- wide spacing
|* Use this guide, experiment and
observe plants and take moisture readings in root zone if
possible. Adapt the guide according to your findings. Remember,
the object is to adequately water the root zone but no more.
Divide the amount of water needed per week by the watering time
to determine the number of waterings weekly. For example, a closely
spaced vegetable garden in medium soil needs to be watered for
2 hours at each watering, and with warm weather the garden needs
6 hours of water each week. Divide six by two and the answer is
three waterings per week. The formula makes it easier to figure
Most home gardens have plants with various watering needs. This
makes it difficult to give each type of planting optimum watering,
but with some care results can be more than satisfactory. Plants
with shallow root zones and shorter watering times benefit from
more frequent applications. Other plants requiring deeper watering
are satisfied by emitters with greater outputs, or in the case
of clay soils, a greater number of emitters.
Knowing the number of gallons delivered per hour by a drip system
is also vitally important. If the delivery rate of a system is
known, one can easily decide how long to leave it on to get the
desired amount of water.
For example, a typical system which delivers 15 gallons per
hour to each 100 square feet of area irrigates at the rate of
1/4 inch per hour. Thus, you would leave the system on for 4 hours
to get a 1-inch irrigation. To apply a 1-inch irrigation to a
garden, run the system long enough to deliver about 60 gallons
for each 100 square feet of garden area. Likewise, a system with
a 30-gallon-per hour rate of delivery would do the same job in
To calculate the delivery rate of a particular drip system,
read the meter again, subtract the first reading from the second
and divide the total gallons per hour by the approximate number
of units of 100 square feet in the garden. Divide the gallons
per hour per 100 square feet by 60 to see what fraction of an
inch is applied in 1 hour.
Another method of measuring the volume delivered by one emitter
in 1 minute is to use a measuring cup or graduated cylinder. Repeat
this for several emitters and take the average. Multiply this
volume by the number of emitters in the system to get the volume
per minute. Multiply this volume by 60 to get volume per hour
and convert this to gallons per hour. Again, divide your gallons
per hour by the number of units of 100 square feet in the garden
to get gallons per hour per 100 square feet.
Probably the easiest method is to install an inexpensive water
meter with automatic shutoff on the faucet. Then attach the hose
which carries the water to the header pipe. Set the water to the
header pipe. Set the meter to deliver the number of gallons needed
to apply in inch of water. This volume would be 60 times the number
of units of 100 square feet in the garden.
Turn on the water and stay nearby to record the time it shuts
off. The elapsed time is how long it took the system to deliver
the inch of water.
For newly seeded gardens the system should be run only a short
time every day for a few days to keep the surface soil from drying
out. Plants loaded with fruit will need an inch of water every
Most people new to drip irrigation notice immediately that the
soil surface is dry except for a circle of moist soil right around
the emitter. The wet circles overlap where emitter holes are closely
spaced. Two examples are the Bi-Wall and Twin-Wall hoses.
Moist surface soil is desirable only when germinating seed.
At other times it is a waste of water because tremendous quantities
evaporate from a wet soil surface. The small circle of moist surface
soil around a drip irrigation emitter is like the tip of an iceberg,
because after a few hours of irrigating a great volume of water
under the emitter has spread out through the soil for several
feet in all directions.
The water which falls gently from the drip hose into the soil
is pulled downward by gravity. It is also pulled sideways, moving
from one tiny soil particle to the next by a force known as capillary
attraction. The slower the water flows into the soil, the greater
is its sideways flow relative to its downward flow.
It is easy to see why water from a drip hose in the row spreads
out several feet in all directions even though only a small circle
of wetness on the soil surface is visible. Actually, the dry surface
soil prevents moisture from evaporating into the air, thus conserving
Very often after spring or fall tillage, especially rototilling,
the soil is fluffy and very loose. This soil will not conduct
drip irrigation water properly. Instead of spreading out and wetting
the entire soil volume in the garden, the water travels almost
straight down. A narrow column of soil will be waterlogged, but
most of the surrounding soil remains dry.
For tilled soil to regain its ability to conduct the water sideways,
soil particles must settle back together after each spading, plowing
or rototilling. Sprinkle irrigate an inch of water on the entire
garden after spring and fall tillage to settle soil particles
so that the soil will conduct water laterally as well as downward.
An inch or two of rain also settles the soil.
Sandy loam soils hold less water per foot of depth than clay
loam soils. Water moves downward faster in sandy soils than in
those with high clay content. Generally, water spreads sideways
more in clay loam than in sandy loam soils, but there are exceptions.
Some homeowners have added so much organic matter to their sandy
soil that the water from an emitter travels outward in a circular
pattern, wetting soil 3 feet away from the emitter to within 3
inches of the soil surface.
In Texas, spring rainfall is often adequate to get plants started.
In June and July rainfall is less, and higher air temperatures
and longer days cause plants and soil to lose much more water
into the air. Watch the weather and record the amount and frequency
of rainfall, remembering that supplemental irrigation may be necessary
even in a rainy week if the required amount has not been supplied
The frequency of irrigation should increase as hot summer weather
approaches. When temperatures reach the high 90's and humidity
is low, fruiting tomato plants require irrigation every other
day with at least an inch of water for maximum production. In
the fall, with the return of more frequent rainfall and cooler
temperatures, allow more time between irrigations. An inch every
5 to 7 days is adequate then.
Inspect plants regularly to determine necessary adjustments
in daily irrigation time. If the zone of moistened soil is increasing
in size, reduce operating time; if the moistened soil zone is
decreasing in size, increase operating time.
The frequency and duration of drip irrigation also depend on
the kinds of plants being grown. For instance, tomatoes use more
water than any other vegetable in the garden when full grown and
laden with fruit.
Three to 6 gallons of water daily usually is sufficient for
a tree during the first and second year after planting. Only 3
to 6 hours of irrigation time are required daily during maximum
water use months if one 1-gallon-per-hour emitter is used at each
Water is a limited and fragile resource. Each gardener utilizes
a small part of the total water consumed, but the total use by
all gardeners is significant. Irrigating home gardens and landscapes
is considered a luxury use of water by many people. Non-essential
use of water implies a special responsibility on the part of gardeners
to efficiently use the resource and to protect its quality.
This responsibility is fulfilled by following the recommendations
in this bulletin concerning water conservation and to further
avoid practices that contribute to surface and groundwater contamination.
Among the threats to pure water are improper use of fertilizers,
pesticides and soil erosion. Label instructions on all pesticides
and fertilizers must be followed faithfully and water run-off
due to excess irrigation should be minimized.
Abscission - The falling off or breaking off of a leaf
or fruit as the result of a weak point which forms at a point
on the petiole or stem.
Bi-Wall drip tubing - A brand of drip tubing which has
a small diameter plastic tube fused to the top side of a large
diameter plastic tube. Water flows through the large tube and
into the small tube through holes spaced every 4 to 6 feet. Water
drips out of the small tubing onto the soil from holes spaced
about 1 foot apart. This system allows water to be distributed
evenly along a relatively long row of up to several hundred feet.
Drip irrigation - The slow application of water, usually
drop by drop, to the soil.
Ear tee - A fitting used to conduct water from a given
point along a header pipe into a length of Bi-Wall or Twin-Wall
tubing. The ears are two semi-rigid loops of plastic that are
looped over the header pipe to prevent the tee from being pushed
out by water pressure.
Emitter - A small fitting (usually in the size range
of an aspirin to a spark plug) with a precisely formed orifice
or channel in it. This emitter is plugged into flexible plastic
pipe permitting water to flow out of the pipe at a very slow rate
at any point along its length.
Evapotranspiration - The combined loss of water from
the soil by evaporation and from leaves by transpiration.
Filter - A device which captures particles of sand or
other matter which might plug orifices in the lateral drip lines.
Fittings - Collectively, the parts of a drip system;
pipe, connecting tees, valves, emitters, etc.
Flow rate - The volume of water passing through a pipe
or out of an emitter.
Flushing - The process of washing captured particles
out of a filter.
GPH - Gallons per hour, a term which specifies the rate
of water flow through a pipe or the amount of water delivered
by a pump.
GPM - Gallons per minute, a term which specifies the
rate of water flow through a pipe or the amount of water delivered
by a pump.
Header - The length of pipe placed along the high side
of the garden to conduct the water into the drip hoses, tubes
or lateral driplines that are laid down along the row.
Hose connector - The fitting connected to a plastic pipe
or garden hose which has hose threads that match the threads on
the house faucet.
Irrigation - Application of water to the soil surface.
Lateral drip lines - Lengths of plastic pipe or tubing,
containing emitters or precisely formed orifices, laid down along
the center of a row of plants.
Line - Another term for plastic pipe or plastic tubing
that is used to transport water along rows of plants or from tree
to tree in a drip system.
Line size - Usually the diameter of a particular pipe
or tubing used to conduct water in a drip system.
Moisture deficit - a condition in which a plant's requirement
for water is greater than the supply available to it, thereby
preventing the plant from reaching its full potential of beauty,
yield and quality.
Mulch - Generally, any organic or inorganic substance
such as hay, lawn clippings, paper or plastic applied to the soil
surface to prevent weed growth and water loss.
Orifice - A precisely formed hole in a plastic pipe or
tube or in a small fitting (known as an emitter) plugged into
plastic pipe through which water flows out in drops or a tiny
Photosynthesis - The formation of glucose by the reaction
of carbon dioxide and water in the green leaf.
PSI - Pounds per square inch, a term used to specify
water pressure to the amount of force pushing on the water in
Root zone - The location of most of a plant's root system
in terms of lateral spread and depth.
Run-off - Water that flows over the surface of the ground
rather than penetrating the soil.
Salts - Chemical elements in the form of dissolved ions
that are carried in irrigation water and deposited in the soil
when water moves into plants or evaporates from the soil surface.
Soil texture - The relative amounts of sand, silt and
clay present in a soil which places it in one of the textural
classes: sand, loamy sand, sandy loam, silty loam, clay loam or
Soil tube - A hollow metal tube that is forced into the
soil to remove a sample of soil.
Soluble salts - Various naturally occurring or introduced
salts such as sodium chloride and calcium which are dissolved
Sprinkler - A device attached to a hose to propel streams
of water into the air, thereby distributin water evenly over a
lawn or garden surface.
Stomates - Tiny pores in the leaf surfaces (more on the
underside) which open and close to allow carbon dioxide gas to
enter and oxygen and water vapor to exit.
Transpiration - The process by which water moves from
the leaf into the air in vapor form.
Twin-Wall drip tubing - A brand of drip tubing which
consists of two plastic tubes, one inside the other, joined by
a seam that runs along the length. The inner tube conducts the
water along the length of the row. It flows into the outer layer
of tubing through tiny holes spaced 4 to 6 feet apart. Then the
water drips out of tiny holes formed every 12 to 18 inches in
the walls of the outer tubing.
This space is provided for you to list the supplies you will
need to build your drip irrigation system.
The information herein is for educational purposes
only. Reference to commercial products or trade names is made with
the understanding that no discrimination is intended and no endorsement
by the Cooperative Extension Service is implied.
Educational programs conducted by the Texas Agricultural Extension
Service serve people of all ages regardless of socioeconomic level,
race, color, sex, religion, handicap or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture
and Home Economics, Acts of Congress of May 8, 1914, as amended,
and June 30, 1914, in cooperation with the United States Department
of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural
Extension Service, the Texas A&M University System.
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