HOME LAWN IRRIGATION
A.J. Powell and M.L. Witt
For best quality landscapes, supplemental
irrigation is almost always necessary during Kentucky summers. If you compare
the long-term average rainfall for Kentucky (46 inches annually) and water
requirements for growing turf and woody plants, you could easily conclude
that lawns and woody plants do not need irrigation. On the other hand,
if you consider the extreme variability in our rainfall and temperatures,
your need for supplemental irrigation is obvious.
How Much Water Should You Apply?
How Much Water Does Your Landscape Need?
Most Kentucky soils can hold about
2/3 inches of plant extractable water in the top 4 inches where most plant
feeder roots persist. Although this amount is less than turf and woody
plants will likely use during a week it is equivalent to about 400 gal
of water/1000 sq ft of landscape area. A common rule of thumb is that turf
and woody plants need about one inch of rainfall or irrigation water/week
from May through September.
Beware of Overwatering
Irrigation is used mainly to supplement
rainfall rather than to provide all the moisture that plants need. Consequently,
irrigation should never be done on some arbitrary, regular schedule such
as daily, every other day, etc. Rather, water should be applied when soil
is dry an inch below the surface; when leaves begin to wilt; when grass
begins to show off-colors like yellow or bluish casts. The exception to
this rule is when you are trying to get a new lawn established. If possible,
seeds need daily (even twice daily) watering to germinate and rapidly develop
in the small seedling stage.
It would be better to let an existing
lawn suffer or die naturally without water, than to kill it with expensive
overwatering. Overwatering causes shallow roots, nutrient loss, disease-susceptible
plants, oxygen deficiency around plant roots, and very severe problems
with weeds like nutsedge, nimblewill, bentgrass, annual bluegrass, oxalis
and crabgrass. Roots must have a balance of water and air; overwatering
In most situations with woody plants,
enough water should be applied at each irrigation to replace water that
was used. If enough water is applied to penetrate deeply and to be absorbed
before further irrigations, deep rooting will be encouraged and crown-rotting
Overwatering stimulates damage to ornamentals
such as Taxus, junipers, azaleas, rhododendrons, Japanese hollies, hemlock,
dogwood, geraniums, chrysanthemums, etc. These plants are susceptible to
diseases such as Phytophthora root rot and Pythium, diseases encouraged
by overwatering. Other ornamentals such as pin oak, river birch, alder,
willow, bald cypress, red maple and sweet gum are much more tolerant of
overwatering. Woody plants planted in drainage areas and planted too deeply
will be most severely affected by overwatering.
Water Use by Plants
To manage irrigation properly, you
need to know how fast water is lost by transpiration (through leaves) and
by evaporation from the soil (evapotranspiration).
Environmental factors that influence
evapotranspiration are sunlight, temperature, humidity and wind. Often
leaves take on a wilted, dull appearance after a strong wind, probably
because of low humidity, high temperature, intense sunlight and mechanical
Large landscape plants use more water
than does grass. Solid plantings of trees and shrubs use 10-20% more water
than turf, whereas a solitary shrub or tree may use 2-3 times as much water
as a comparable area of turf because it has greater exposure to sun and
Evapotranspiration varies greatly during
the year for evergreens and turf, but it varies even more for deciduous
plants. In summer, deciduous plants may use 40% more water per day than
broadleaved evergreens of similar size.
Let Your Plants Tell You When to Water
Turf is too dry when:
•turf on high spots and/or south slopes
starts to show some chlorosis or turns bluish-gray in color;
•footprints remain in grass long after
•soil from the root zone is dry or
•no rain has occurred for about one
week and hot, dry, sunny, windy weather persists.
Woody plants are obviously too dry when:
•leaves that were shiny become dull;
•bright green leaves fade to gray-green;
•leaves begin to wilt or curl;
•dead areas appear on the edges of
However, the same symptoms of wilting,
curling and leaf chlorosis show up when plants are growing in soils that
are too wet.
The very best way to determine if you
need to irrigate is to probe the surface soil and determine if the top
inch or two is visibly dry. You may even want to pick up a handful of soil
and mold it into a ball. If the ball crumbles when rubbed, the moisture
is probably about right. If the ball will not crumble when rubbed, the
soil is too wet. If the soil will not mold into a ball, it is too dry to
adequately supply water to plants.
Guidelines for Watering?
Not all sites in a landscape will need
the same frequency of irrigation. If, for example, you are watering a flower
bed under a roof overhang, you may need irrigation even during rainy spells,
especially on east and north sides of buildings. Probe the soil and see!
Newly set annual flower transplants need water every other day for a week
or two until roots have a chance to grow. You need to check your plants
often for signs of water stress and apply water as needed.
More frequent irrigation is usually
•on hotter, south-facing slopes;
•where turfgrass has 1/2-inch or greater
of turf thatch;
•when growing Kentucky bluegrass rather
than tall fescue;
•when mowing at 1 1/2-inch height rather
than 2 1/2-inch height;
•around newly planted landscape plants;
•certainly during the hottest time
•for the first 2 years after planting
trees and shrubs; nothing is more important to keeping them alive and reestablishing
the root system than regular watering.
During summer vacations and other summer
periods when you cannot give close attention to the landscape, consider
having someone check your turf and woody plants every week and then irrigate
if needed. During fall and spring, when temperatures are cooler, the lawn
and established woody plants can usually go 2 to 3 weeks without significant
rainfall or irrigation.
When necessary to irrigate, apply about
2/3-inch of water. Check the irrigation rate and uniformity by placing
straight edged cups or pie pans around several lawn and landscape bed areas.
Also probe the soil to see if it is wet approximately 3 to 4 inches deep
after irrigation. If surface run-off occurs before irrigation is complete,
apply only 1/2 of the amount and wait a few hours for additional irrigation.
An efficient irrigation wets only the active root zone, does not saturate
the soil and does not cause run-off.
How to Apply Water to Trees?
Trees should be watered with soaker
hoses rather than overhead. A slow running garden hose, trickle system,
leaky pipe system or any other method you can think of to get water localized
in the root ball area, at a very slow rate, for a couple hours is the best
way to water trees.
Directing a stream of water over the
root system for a few minutes does little good if the soil is heavy. The
amount of water entering the root system is limited by the infiltration
capacity of soil; many soils can only take in water at a rate of one or
two inches per hour and heavy clay soils may only absorb 0. 1 inches per
hour. Therefore, the amount of time for soaking is much more important
than the rate of application.
Drip irrigation systems are now available.
These often improve water infiltration because they can be timed to apply
a small amount of water for a long period of time. In addition, since water
is applied below the plant foliage, leaves do not get too wet and fewer
disease problems develop. If a root ball is thoroughly wetted, additional
irrigation may not be needed for several weeks.
What Time of Day?
Water can be applied anytime during
the day without damaging turf. However, more water evaporates during the
heat of day. Early morning watering is often advantageous since it removes
dew and guttation water that often encourages disease problems. If a turf
disease is evident, avoid late evening watering that would prolong leaf
wetness. Otherwise watering during late evening or night causes no problems.
Automatically time-controlled underground
lawn irrigation systems have become readily available in Kentucky. When
systems are properly designed and installed, they can be effectively used
to grow high-quality landscapes.
When compared to hand-watering with
hoses and sprinklers, these automatic systems give more uniform coverage
and can reduce water loss by keeping water off sidewalks, streets and buildings.
In addition, irrigation can be automatically scheduled to avoid peak residential
water demand, which is important when using municipal water.
Overwatering is the biggest mistake
made by homeowners utilizing automatic irrigation systems. Although an
automatic timer may be set to irrigate several times a day, everyday and
at various time intervals-DONT. Instead, use good judgment to decide when
irrigation is needed. Then either (1) manually set the clock to automatically
rotate through different stations (valves/zones); (2) program the system
for one irrigation to occur, for example the next morning; or (3) set the
automatic timer to provide one or two irrigations per week with either
automatic or manual cutoff if significant rainfall or mild weather occur.
However it is best and most economical to initiate watering only when drought
Drip and Trickle Irrigation
Drip and trickle irrigation systems
deliver very small amounts of water directly to the root zone. Water reaches
the root zone through a network of pipes, usually consisting of a large
main line and smaller laterals running to individual plants or among plants
in a landscape bed.
Drip and trickle systems have advantages
and disadvantages, but the advantages far outweigh the disadvantages:
1. A high degree of water control is possible. It can supply plants
with the precise amount of water they need.
2. Smaller water supplies can be utilized. Drip requires roughly 50%
less water than sprinkler or surface irrigation.
3. Lower operating pressures and lower flow rates are required.
4. Disease and insect damage is reduced because leaves are not wetted.This
advantage is very important in woody plants like roses.
5. Weed problems and cultivation costs are reduced because water is
not lost to weed growth between plants.
6. On hilly terrain, good systems can operate efficiently with no water
runoff and without interference from the wind.
The main disadvantage is plugging of
the system's small orifices with soil, sand, algae or mineral precipitates.
Proper filtration reduces these problems. Other drawbacks:
•Moisture distribution is limited.
•Rodents and insects may damage some
•Occasionally, as people walk over
the area where it is installed, they may damage the tubes.
Although somewhat inconvenient and
time-consuming, the most common and least expensive method of irrigation
involves attaching a single sprinkler to a portable hose. Oscillating (wave)
sprinklers can be used to effectively irrigate rectangular areas; but because
they generally throw small droplets high into the air, much water is lost
in evaporation. Fixed spray sprinklers are particularly good for watering
individual plants or hot-spots in a lawn, but often apply water non-uniformly
to large lawn areas. Rotary sprinklers usually apply a higher rate of water,
but only in a circular pattern. Even distribution is therefore most difficult
unless the sprinkler is moved very often so that watered areas overlap
each time. Soaker hoses are suitable for steep slopes and narrow beds or
areas between the sidewalk and street; again, distribution is often uneven
and the hose's quality quickly deteriorates.
You can easily check the rate and uniformity
of water application by placing a row of cans or pie pans in a line at
1-3 ft intervals from the sprinkler to the point of furthest throw. By
allowing the sprinkler to run for 1/2 or one hour, you can then evaluate
its quality and the inches per hour it delivers.
In summary, remember that extra water
from irrigation may only be needed, or even desirable, during the most
severe droughts. If you just irrigate particular hot spots, shallow soil
areas, or drought-susceptible plants, your irrigation program will be less
costly and unlikely to cause problems for many plants that suffer from