by Jerry Parsons, Ph.D.
Horticulture Specialist, Texas Agricultural Extension Service
in San Antonio
Has your water bill reached astronomical proportions?
Maybe an evaluation of your watering methods will result in
more efficient use of the available water and at the same
time reduce the amount you are using. First, check your methods
of application. There is no use in applying water any faster
than the soil will soak it up. If applied faster than this,
the surplus will either flow into the street or else flood
your neighbor. Sandy soil will usually absorb water almost
as fast as water can be applied but tight clay soils will
absorb water very slowly. Select the method of application
that best fits your soil type. Drip irrigation systems for
shrubs makes the most efficient use of water for beds.
Secondly, use a mulch wherever possible. A
good mulch of grass clippings, pine bark or dry leaves conserves
moisture, prevents compaction, keeps soil temperature lower,
reduces weed population and in case weeds and grass do get
a start, they are much easier to pull if a mulch has been
used. Periodically check the depth of the mulch material.
Organic mulches tend to decompose or sometimes wash away,
so frequent checks and replacement where necessary will help
While night-time watering can be conductive
to development of plant diseases, one does get more efficient
use of the water in the early morning and late evening when
evaporation rates are lowest.
Last, but by no means least, is the practice
of doing a thorough job of watering each time it becomes necessary
to irrigate. A thorough watering at 7- to 10-day intervals
encourages deep root penetration and full utilization of the
available soil moisture. Just because plants happen to wilt
during the heat of the day doesn't mean the soil is dry. If
plants remain wilted until morning then the addition of water
Don't stop watering completely as plants can
die due to moisture shortage during periods of high temperature
and high wind movement. Just remember to use the precious
resource as efficiently as possible.
One of the best uses of a valuable resource such as water
is to insure the survival of recently established plants.
Summer is a critical period for recently planted shade trees
and ornamental plants. Not yet completely recovered from the
effects of transplanting, they often need special care to
withstand dry weather conditions.
Water is a recently established plant's prime
need. Hot summer days and drying winds take a great deal of
moisture from the leaves and stems. This water must be replaced
through root absorption of soil water. When transplanting
a balled-and-burlapped tree (roots of container grown trees
and shrubs are not removed), most of its wide-spreading, deep-growing
roots are cut. In its new location, the only water which a
newly established tree can utilize is that which is in the
soil close to the tree. If this soil area becomes dry, the
leaves wilt, turn brown and drop. Death of many branches or
even the entire tree or shrub can follow.
It is wise to water at regular intervals all
trees planted within the past year. IF the soil is sandy,
water once a week; if it is clay or loam, thorough watering
every ten days or two weeks should suffice. Using an open-end
hose, regulate the water flow so there is no run-off and let
it flow until the soil around the tree is saturated.
If the tree or shrub was worth planting, it
is certainly worth the little extra effort required to keep
it in good growing condition.
WATERING VEGETABLES AND FLOWERS
The only fate worse than thirst for a plant
is death. In fact, they often accompany one another! Even
if some folks are wise enough to know when to water a thirsty
plant just seconds before it crosses death's threshold, these
procrastinators are still losers. When a plant thirsts and
is severely stressed, overall vigor and production is decreased.
This is especially true of plants which are expected to produce
fruit. Not only will total yield be decreased, but fruit quality
will also decline. Carrots, onions and tomatoes start cracking!
Eggplant fruit gets bitter! Shrubs mysteriously die! Flowers
bloom with mediocrity! Trees do not grow rapidly! The house's
foundation cracks! What is causing all of these calamities?
Lack of and improper application of water is the culprit of
all of these problems.
Most people don't intentionally make their
plants suffer. There are three categories in which the thirst
inflictors fall - - those who don't know when to water, those
who don't know how to water and those who are so absent-minded
they forget. Some may qualify for more than one of these categories.
How do you know when to water? Some people
say water when the plant wilts. When a plant wilts, it is
obviously in a stressed condition and the damage (foliage
burn, foul-tasting fruit, production loss) has already occurred.
Besides, does the wilting of a plant indicate drought? I have
seen wilted plants standing in water, i.e., they were water-logged.
Plants wilt with root rot diseases. So wilt is the worst possible
indication. Soil moisture is the best criterion for watering.
If the soil moisture is adequate, don't water, even if the
plant is wilted. To test for soil moisture, probe around plants
with your finger. If the soil is moist several inches deep,
your plant is alright.
Rooting depth is the most limiting plant characteristic
in relation to water uptake. Crops with shallow root systems,
such as onions and celery, require more frequent irrigations
than deep-rooted crops such as pumpkins, tomatoes, and watermelons.
Very shallow rooted crops include celery, lettuce, onion,
radish; shallow-rooted crops include broccoli, cabbage, cauliflower,
Chinese cabbage, cucumber, muskmelon, pepper (transplanted),
spinach, and tomato (transplanted); intermediate rooted crops
include bean (snap), beet, carrot, eggplant, pea, pepper (seeded),
rutabaga, and summer squash; deep-rooted crops include asparagus,
beans (lima), parsnip, pumpkin, winter squash, tomato (seeded),
and watermelon. The most critical stages of growth of vegetable
crops when moisture stress is the most damaging to yields
is asparagus (fern growth), snap bean (pod-filling), broccoli
(establishment, head development), cabbage (establishment,
head development), carrot (establishment, head development),
cauliflower (establishment, head development), celery (establishment,
rapid growth during hot periods), sweet corn (tasseling, silking,
and ear filling), cucumber (flowering, fruit enlargement),
eggplant (flowering, fruit development), lettuce (head development),
muskmelon (flowering, fruit enlargement), onion (bulb enlargement),
pea (flowering, pod-filling), pepper (transplanting, fruit
set and development), squash pumpkin (flowering, fruit development),
radish (root enlargement), summer squash (flowering, fruit
development), tomato (flowering, fruit set and enlargement)
and turnip (root enlargement).
Now that you know when to water, you may not
know how. The "how" may be the most important part.
First of all, plants need to be deep watered to stimulate
a larger root system. This larger root system will be advantageous
in utilizing every drop of available moisture during periods
of severe drought. Deep watering involves soaking.
Floor or furrow irrigation, a technique used
by some farmers, involves mounding the soil into raised beds
(mounds on which to plant) and running the water down the
furrows between the beds. The bed centers or rows are spaced
at least 30 inches apart. The bed soil is firmed to enable
it to conduct water to the top of the bed. In this way, moisture
will reach the roots of young plants. The ditches or furrows
between these rows are "flooded" or filled with
water. The roots of the plants growing in rows on the beds
have direct contact with the water supplied. This technique
results in deep soaking which encourages vigorous development
of root systems.
The most obvious disadvantages of this type
of irrigation is water use. The system involves wetting the
entire garden rather than just the area where plants are growing.
A sprinkle system has the added disadvantage of wetting the
plant foliage which can encourage plant diseases.
There is an easier way to deep water. It is
called drip irrigation. "Drip or trickle" irrigation
is a unique method of irrigation. It allows precise applications
of water in the immediate vicinity of plant roots. Soil moisture
in the area around the plant is maintained at a uniformly
high level throughout the growing period. Small amounts of
water are applied frequently, perhaps daily, to replace that
withdrawn by soil evaporation and plant transpiration. Growth
and production of a plant is greater when they are not subjected
to wet and dry cycles which normally occur with other irrigation
methods. This is very apparent in situations where plants
are growing near a leaking faucet. Such plants always out
perform neighboring plants. This has often been verified in
tests throughout the country. Data indicates that tomatoes
can yield 30-40 percent more fruit and peppers as much as
30 percent more fruit when grown with drip irrigation. All
of this increase in production occurs even though much less
water is used. Distribution and evaporation losses are minimized.
Less of the total soil area is fully wetted than with sprinkler
and furrow systems. Normally, only 25 percent of the soil
surface is wetted with drip. This significantly reduces the
amount of water required for irrigation.
Drip irrigation also simplifies your irrigation
procedures and reduces labor requirements. This is imperative
if you have a family which is allergic to dirt and sweat who
will let plants die of thirst when you are away if an easy
watering technique is not available. Drip systems can be easily
activated from one faucet. A drip irrigation system also takes
care of the third category of thirst inflictors who "forget"
to water certain plants. Once the drip hose is installed around
shrubs and vegetables, it never "forgets" to water
- - it specifically waters each and every plant. Of course,
you must remember to activate the drip system for three hours
a day every other day by turning the water faucet on. If you
can't remember that, then you are too derelict to be entrusted
with plants anyway! In case you can remember to turn the water
on BUT NOT to turn it off, simply purchase a water timer device
which will "remember" for you.
So before the dry weather destroys your plants,
spread a little happiness around - - install a drip system.
"Spring has sprung; fall has fell; summer
is here; and it's hotter than...it should be!" and "drier
than it should be" should also be included in this rhyme.
If Texans expect to survive this dry summer, we HAVE to be
water smart, i.e., utilize our most precious resource, water,
wisely. Over the last seven years, researchers have made advances
in understanding turfgrass water use rate (WUR). The idea
is to develop grass systems that lose less water to the atmosphere
and maintain more favorable soil moisture condition for plant
However, people must understand that low water
use does not necessarily mean less irrigation. For instance,
taller mowed grasses have higher WUR than shorter mowed grass,
but the amount of irrigation needed to keep turfs at acceptable
levels is less for the taller grass than the shorter.
The two major aspects of mowing that influence
water use are height and frequency. Grasses mowed at higher
cutting heights have a reduced canopy resistance and, therefore,
use more water than short mowed grass. Mowing frequently and
at a short height increases turf density. Dense turf resists
the upward movement of water vapor through the turf canopy.
A dense turf with a tight canopy also resists air movement
down into the turf canopy. The net result is less moisture
lost from the turf canopy to the atmosphere. This process
ultimately reduces turfgrass evapo-transpiration (ET). With
higher mowed turf the leaf canopy that expands above the mowing
height is less dense. This allows for more air mixing that
results in higher water use rates. It is important to note
that taller grass transpires more water, but has a more extensive
root system that draws water from a larger soil reservoir
than shorter grass. Thus, taller grasses avoid soil drought
and plant wilt by expanding their roots into soil areas with
In contrast, lower mowing heights result in
limited root systems that need more frequent irrigation to
supply water to a shallower root system. To reduce irrigation
needs, one should mow frequently at the highest feasible height.
These management practices enhance canopy resistance and minimize
detrimental rooting responses.
Proper fertilization is also important, if
not critical, to effective water use on lawns. The primary
goal of turf fertilization should be an increased shoot density
with less emphasis on a darker green color. People should
strive to meet, but not exceed, the nutritional needs of the
Nitrogen is the primary nutrient used to regulate
turfgrass density and color. Water use rate increases with
increased nitrogen nutrition. This occurs because leaf expansion
above the normal mowing height occurs at a much faster rate.
Leaves forced into this upper boundary layer lose water at
a faster rate because they are in an area of greater air movement
and reduced canopy resistance.
Over-stimulation of growth with nitrogen is easily detected
by an increased need for mowing. Under these conditions, turf
will have high WUR, and rooting development will be reduced.
In time, excessive leaf growth will demand a greater water
supply that cannot be met by the reduced root system. Turf
wilt occurs more frequently as this imbalance develops. What
follows is usually a decision to increase the frequency -
and sometimes the amount - of irrigation to offset the symptoms
of wilt. In this case, a poor functioning root system resulted
from an increased water demand. This increase was, in turn,
caused by improper nitrogen fertilization and frequent irrigation.
People interested in conserving water should use the lowest
amount of nitrogen that gives the desired turfgrass quality
and function. This was the basis for the Extension recommendation
of only two fertilization applications annually -- a slow
release in the spring after the second mowing has occurred
and a Winterizer analysis in October.
Potassium and iron are two additional elements
that may give an extra edge in managing turf exposed to drought
stress. Potassium and iron have been reported to increase
root growth which may account for their role in reducing wilt
and improving drought avoidance. Reduced levels of nitrogen
combined with iron can result in turf greening similar to
normal rates of nitrogen. The implication here is that applications
of iron plus nitrogen, especially in the spring, will result
in a lower rate of vertical leaf growth and reduced WUR.
Current irrigation practices have probably
involved partly as a result of the equipment available for
irrigation rather than a complete understanding of turfgrass
water needs. Manual sprinkler systems required a lot of time
and trouble for a single irrigation. When using these systems,
it is desirable to provide as much water as possible during
a single irrigation. Irrigate as deeply and infrequently as
possible to promote an extensive root system. The main purpose
for irrigating deep (to the bottom of the effective root zone)
and infrequently is to develop an extensive root system that
continually expands into regions of available soil moisture.
This prepares the plant to avoid soil drought.
The main disadvantage of irrigating too frequently
has been cited as a shallow root system that becomes dependent
on continued frequent irrigation.
For more comprehensive information about watering
and mulching, see
"Efficient Use of Water in the Garden and Landscape"
for low-cost/low-maintenance landscapes"